CA1150835A - Apparatus for recovering a video signal from a video disc - Google Patents

Abstract

ABSTRACT

Apparatus for use in a signal recovery system for recover-ing a video signal from a video disc, the signal including luminance information, chrominance information and periodic chrominance bursts having a prescribed amplitude, wherein the signal is recorded in a succession of light reflective and light non-reflective regions forming a plurality of substantially circular and concentrically arranged tracks, and therein the system includes a focusor for a beam of radiation onto a selected track as the disc is rotated at a prescribed angular velocity and a detector for detecting a reflected beam of radia-tion having an intensity modulated by the recorded video signal, the gain of the higher frequency portion of the spectral response of the signal recovery system decreasing as the radius of the selected track decreases, thereby causing a corresponding variation in the respective amplitudes of the chrominance and luminance portions of the recovered video signal, the apparatus operating to correct for the variable gain of the system by controllably amplifying the corresponding portion of the fre-quency spectrum of the recovered video signal, the apparatus comprising: a detector for detecting the amplitude of the suc-cessive chrominance bursts in the recovered video signal and for producing a corresponding control signal; and an amplifier for amplifying the video signal recovered from the disc, the control signal being coupled to the amplifier to controllably adjust its gain for a frequency band corresponding to the higher frequency portion of the recovered video signal, thereby correct-ing for the variable gain of the signal recovery system.

Description

i~50835 VIDEO DISC PLAYER
TECHNICAL FIELD
The present invention relates to the method ~nd means rOr reading a frequency modulated video sign~l stored in the form o~ successively positioned re~lectlve and non-reflective regions on a plurality o~ in~orma'ion tracks carried by a video dlsc. More specifically, an optical system ls employed for directlng a reading be~
to impinge upon the information track and for gather'n~
10 ~the re~lected signals modulated by the reflective and non-rerlective regions o~ the information trac~. A
rrequency modulated electrical slgnal is recovered rrom the reflected light modulated signal. The recovered - ~requency mGdulated electrical signal ls applled to a signal processing section wherein the recovered rre-quency modulated signal is prepared for applicatlon to a standard television receiver and/or monitor. The recovered llght modulated signals are applied to a plurality of servo systems for providlng control sign~ls which are employed ~or keeping the lens at the optim~m rOcus position with relation tothe inrormatlon bearing surrace Or the video disc and to maintaln the rocused light beam ln a position such that the focused llght spot lmpinges at the center o~ the in~ormation track.
BRIE~ S~ ;R~ OF THE INVEN~ON
The present lnvention is directed to a vldeo disc player operating to recover rre~uency modulated video slgnals rrom an inrormatlon bear~ng æurrace Or a video disc. The rrequency modulated video in~ormati~n ;, is stored in a plurality of concentrlc clrcles or a slngle splral extendlng over an lnformatlon bearlng portion of the video dlsc surface. The frequency modu-lated video signal ls represented by indlcla arranged in track-like fashion on the lnformation bearing surface portion of the video disc. The lndicia comprlse suc-cesslvely positloned reflective and non-rerlective regions ln the information track.
A laser is used as the source of a coherent llght beam and an optical system is employed for ~ocus-ing the llght beam to a spot hav~ng a diameter approxl-mately the same as the width of the indicia positioned ln the information track. A microscopic ob~ective lens is used for focusing the read beam to a spot and for gathering up the reflected llght caused by the spot lmplnglng upon successively positioned light reflective and li~ht non-reflectlve regions. The use of the mlcroscopically small lndlcia typlcally 0.5 mlcrons in ~ wldth and ranglng between one mlcron and 1.5 microns ln length taxes the resolvlng power of the lens to lts fullest. In thls relationshlp, the lens acts as a low pass filter. In the gathering of the reflected light and passing the reflected light through the lens when operatlng at the maximum resolutlon of the lens, the gathered light assumes a slnusoldal-shaped llke modulat~
beam representlng the frequency modulated vldeo signals contained on the vldeo dlsc member.
The output from the microscopic lens is ap-plied to a signal recovery system wherein the reflected 3 light beam is employed flrst as an lnformation bearlng light member and second as a control signal source for generatlng radial tracking errors and focus errors.
The lnformatlon bearlng portlon of the recovered fre-quency modulated vldeo signal is applied to an FM
3~ processing system for preparation prlor to transmlssion to a standard TV receiver and~or a TV monitor.
The control portion of the recovered frequency modulated video signal is applied to a plurallty Or servo subsystems for controlllng the position of the reading beam on the center of the informatlon track and ~or controlling the placing of the lens for gathering the maximum reflected light when the lens ls posltloned at lts optimum ~ocused posltion. A tangentlal servo subsystem is employed ror determining the time base error introduced into the reading process due to the mechanics of the reading system. This time base error appears as a phase error in the recovered frequency modulated video signal.
The phase error is detected by comparing a selected portion of the recovered frequency modulated signal with an internally generated signal having the correct phase relationship with the predetermined por-tion o~ the recovered frequency modulated video signal.
The predetermined relationshlp is established during the original recording on the vldeo disc. In the pre-ferred embodiment, the predetermined ~rtion of the recovered frequency modulated video signal is the color burst signal. The internally generated reference rrequency is the color subcarrler frequency. The color burst signal ~as originally recorded on the video disc under control of an identical color subcarrier ~re-quency. The phase error detected in thls comparison process is applied to a mlrror moving ln the tangential direction which ad~usts the location at which the ~ocused spot implnges upon the information track. The tangential mirror causes the spot to move along the lnformation track either in the ~orward or reverse directlon for providing an adJustment equal tothe phase error detected in the comparison process. The tangentlal mlrror ln its broadest sense is a means for adJusting the time base of the signal read from the video disc member to ad~ust ~or time base errors inJected by the mechanics of the reading system.
In an alternative rOrm of the inventlon, the predetermined portlon Or the recovered ~requency modu-lated vldeo signal is added to the total recorded frequency modulated video signal at the time of record-ing and the same ~requency is employed as the operating `

, point for the hi~hly controlled crystal oscillator used in the comparison process.
In the preferred embodiment when the video disc player is recovering frequency modulated video slgnals representins televislon pictures, the phase error comparison procedure is performed ror each line Or television information. The phase error ls used for the entire line of television information for correcting the time base error ror one full line of television informa-tion. In this manner, incremental changes are appliedto correct for the time base error. These are con-stantly being recomputed for each line of television information.
A radial tracking servo subsystem ls employed 15 for maintaining radial tracking Or the focused llght spot on one information track. The radial tracking servo subsystem responds to the control signal portion of the recovered frequency modulated signal to develop an error signal indicatlng the offset from the preferred center of track position tothe actual position. Thls - tracking error ls employed for controlling the movement of a radial traclcing mirror to bring the light spot back into the center of track position.
The radial tracking servo subsystem operates in a closed loop mode o~ operation and in a~l op~n ~oop mode of operation. In the closed loop mode of operation, the diff~rential tracking error derived from the re-covered frequency modulated video slgnal ls contlnuously applied through the radlal tracking mirror to bring the focus spot back to the center of track position. In the open loop mode Or operation, the differential tracking error is temporarily removed from controlling the operation of radial tracking mirror. In the open loop mode of operation, various combinations of signals take over control of the movement of the radial track-ing mlrror for directing the point of impingement Or the focused spot from the preferred center of track position on a first track to a center of track position on an adjacent track. A first control pu~ causes the tracking mirror to move the focused spot o~ llght from the center Or track position on a first track and move towards a next adjacent track. This first control pulse terminates at a point prlor to the focused spot reaching the center of track position ln the next ad~acent track.
After the termination of the first control pulse, a second control pulse is applied to the radial tracklng mirror to compensate for the additional energy added to the tracking mirror by the first control pulse. The second control pulse is employed for bringing the rocused spot into the preferred center of track focus position as soon as possible. The second control pulse is also employed for peventing oscillation of the read spot about the second information track. A residual portion of the differential tracking error is also applied to the radial tracking mirror at a point cal-culated to assist the second control pulse in bringing the focused spot to rest at the center of track focus ~ position in the next ad~acent track.
A stop motion subsystem is employed as a means for generating a plurality of control signals for application to the tracking servo subsystem to achieve the movement Or a focused spot tracking the center of a first in~ormation track to a separate and spaced loca-tion in which tlle spot begins tracking the center of the next adjacent information track. The stop motion subsystem performs its function by detecting a predeter-mined signal recovered from the frequency modulated video signal which indicates the proper position within the recovered frequency modulated video signal at which time the ~umping operation should be lnitiated. m ls detection function is achleved, in part, by lnternally generating a gating circuit indicating that portion of the recovered frequency modulated video slgnal within 3~ whlch the predetermined slgnal slould be located.
In response to the predetermlned signal, whlch ls called ln the referred embodlment a whlte flag, the stop motion servo subsystem generates a first control signal for application to the tracking serYo subsystem i ~50835 fcr temporarily interrupting the appllcation Or the differential tracking error to the radial tracklng mirrors. The top motion subsystem generates a second control signal for application tothe radlal tracking mirrors for causing the radial tracking mirrors to leave the center of tracking position on a flrst information track and ~ump to an adjacent information track. The stop motion subsystem terminates the second control signal prior to the focus spot reaching the center of the focus position on the next adjacent information track.
In the preferred embodiment, a third control signal is generated by the stop motion subsystem at a time spaced from the termination of the second control pulse. The third control pulse is applied directly to the radial tracking mirrors for compensatin~ for the effects on the radial tracking mirror which were added to the radial tracking mirror by the second control pulse. ~ile the second control pulse is necessary to ~ have the reading beam move from a first information track to an ad~acent lnformation track, the spaces in-volved are so small that the ~umping operztion cannot al~ays reliably be achieved using the second control signal alone. In a preferred embodiment having an im-proved reliable mode of operation, the third control signal is employed for compensating for the effects of ! the second control ~ump pulse on the radial tracking mirror at a point in time when it is assured that the focus spot has, in fact, left the first information track and has yet to be properly positioned ln the center of the next adjacent information track. A further em-bodiment gates the differential error signal through to the radial tracking mirror at a time calculated for the gated portion of the differential tracking error to assist the compensation pulse in bringing ~he focus spot under control upon the center Or track posltion of the next ad~acent informatlon trac~.
The video disc player employs a spindle servo - subsystem for rotating the video disc member positloned upon the spindle at a predetermined fre~uency. In the .i .

preferred embodlment the predetermlned rrequency ls 1799.1 revolutlons per minute. In one revolutlon of the video disc, a complete ~rame of televislon lnforma-tior. is read from the vldeo dlsc, processed in elec-tronic portlon of the video disc player and applied to astandard television receiver and/or televislon monitor in a form acceptable to each such unit, respectively.
~oth the television receiver and the television monitor handle the signals applied thereto by standard internal clrcuitr~ and display the color, or black and white signal, on the receiver or monitor.
The spindle servo subsystem achieves the accur-ate speed of rotation by comparing the actual speed of rotation with a motor reference frequency. The motor reference frequency is derived from the color sub-carrier frequency which is also used to correct for time base errors as described hereinbefore. ~y utiliz-ing the color subcarrier frequency as the source Or the ~ motor reference signal, the spindle motor itself removes all flxed time base errors which arise from a mismatch-ing of the recording speed with the playback speed. The recording speed is also controlled by the color fre-quency subcarrier frequency~ The use of a slngle highly controlled frequency in both the recording mode and the reading back mode removes the maJor portion of tlme base error. Whlle the color subcarrier frequency is shown as the preferred source in generatlng the motor rererence frequency, other highly controlled frequency slgnals can be used ln controlling the wrlting and readlng of frequency modulated video signal on the video disc.
A carriage servo subsystem operates in a close loop mode of Gperation to move the carriage assembly to the speclfic locatlon under the direction of a plurality of current generators. The carrlage servo subsystem controls the relatlve posi1;icning of 'he video dlsc and the optlcal system used to form the read beam.
A plurality of individual current sources are lndlvldually activated by command signals from the . ~

8 ~150835 functlon generator ~or dlrectlng the movement Or the carriage servo.
A first command signal can dlrect the carriage servo subsystem to move the carriage assembly to a predetermined location such that the read beam lnter-sects a predetermined portlon of the inrormatlon bear-ing surface of the vldeo disc member. A second current source provides a continuous blas current for directing the carrlage assembly to move ln a fixed directlon at a predetermined speed. A further current source generates a current signal of rixed magnitude and variable length for moving the carriage assembly at a high rate of speed in a predetermined direction.
A carriage tachometer current generating means is mechanlcally connected to the carriage motor and is employed for generating a current indicating the instantaneous position and speed of the carriage motor.
The current from the carriage tachometer is compared , with the sum of the currents being generated ln the current sources in a summation circult. The summation circuit detects the difference between the current sources and the carriage tachometer and applies a different signal to a power amplifier for moving the carrlage assembly under the control of the current generators.
PRIEF DESCRIPTION OF THE DRA~NGS
The foregolng and other ob~ects, features and advantages of the invention will be apparent from the following more particular description Or a prererred 3 embodiment of the invention as illustrated ln the accompanyIng drawings wherein:
FIGURE ~ shows a generalized block diagram of a video disc player;
FI~URE 2 shows a schematlc diagram of the opti cal system employed wit~ reference to the video disc pl~yer sho~Jn in Flgure l;
FIGUR~ 3 shows a block diagram of the spindle servo subsystem employed in the video disc player shown in Figure l;

g i~ 835 FIGURE 4 shows a block diagram of the carrlage servo subsystem employed ln the video disc player shown in Figure l;
FIGURE 5 shows a block diagra~ of the focus 5 servo subsystem employed ln the vldeo disc player sho~n ln Figure l;
FIGURES 5a, 6b, and 6c show various waveforms illustr~ing the operation of the servo subsystem sho~n in Figure 5;
FIGURE 7 shows a partly schematic and partly block diagram view of the signal recovery subsystem employed in the video disc player shown in Figure l;
FIGURE 8 shows a plurality of waveforms and one sectional view used in explaining the operation of the signal recovery subsystem shown in Figure 7;
FIGURE 9 shows a block diagra~ of the tracklng servo used in the video disc player shown in Figure l;
FIGURE 10 shows a plurality of waveforms ~ utilized in the explanation of the operation Or the 20 tracking servo shown in Figure 9;
FIGURE 11 shows a block diagram of the tangen-tial servo employed in the video disc player shown in Figure l;
FIGURE 12 shows a block diagram of the stop motion subsystem utilized in the vldeo disc player of Figure l;
FIGUP2S 13A, 13~, and 13C show waveforms gen-erated ln the stop motion subsystem shown with reference to Figure 12;
FIGURE 14 is a generalized block diagram of the FM processing subsystem utillzed in the video disc player shown with reference to Figure l;
FI~URE 15 ls a block dlagram of the FM correc-tor clrcuit utillzed in the FM processing clrcuit shown in Figure 14;
FIGUR~ 15 shows a plurality of waveforms and one transfer function utillzed in explaining the opera-tion of the FM corrector shown in Flgure 15;
FIGURE 17 is a block diagram Or the FM

-.

~'150835 detector used in the FM processing clrcuit shown ln Figure 14;
FIGU~E 1~ shows a plurality of waveforms used ln explaining the oper~tion of the FM detector shown wlth 5 reference to Fi~ure 17;
FIGUR~ 19 shows a block diagram of the audlo processing circuit utilized in the video disc player shown with reference to Figure l;
FIGURE 20 shows a block diagram Or the audio demodulator employed in the audio processing circuit utilized in the video disc player shown with reference to Figure 19;
FIGUR~ 21 shows a plurality of waveforms useful in e~plaining the operation of the audio demodulator sho~n ~th reference to ~igure 20;
FIGURE 22 shows a block diagram Or the audio voltage controlled oscillator utilized in the audio processing circuit shown with reference to Figure 19;
, FIGURE 23 shows a plurality of waveforms avail-20 able in the audio voltage controlled oscillator shown with reference to ~igure 22;
FIGU~E 24 shows a block diagram of the RF modula-tor utilizing the video disc player shown in Figure l;
FIG~ 25 shows a plurality of waveforms uti-lized in the explanation of the ~F modulator shown with reference to Figure 24;
FIGURE 26 shows a schematic view of a video disc member illustrating the eccentriclty effect Or uneven cooling on the disc;
FIGURE 27 is a schematic view of a video disc illustrating the eccentricity effect of an off-center - relationship of the information tracks to the central aperture;
FIGURE 28 is a logic diagram demonstrating the normal acquire focus mode of operation Or the focus ser-/o emploJed in the video disc sho~n in Figure l; ~nd FIGURE 29 is a logic diagram demonstrating other modes of operation Or the focus servo shown wlth reference to Figure l;

~;

--1i--DETAILED DESCP.IPTION OF THE I~'ENTION
The same numeral will be used in the several views to represent the same element.
Rererrins to Figure 1, there is shown a sche-matic bloc~ diagram of a video disc player system in-dicated generally at 1. The player 1 employs an optical system indicated at 2 and shown in greater detail ln Figure 2.
Referring collectlvely to Figures 1 and 2, the optical system 2 lncludes a read laser 3 employed for generating a read beam 4 which ls used for readln~ a frequency modulated encoded signal stcred on a video disc 5. The read beam 4 is polarlzed ln a predeterminQd dlrectlon. The read beam 4 ls directed to the vldeo dlsc ~ by the optical system 2. An additional functi3n Or the optlcal system 2 is to focus the light beam dc.~n to a spot 6 at its point of lmpingement with the video disc 5.
~ A portion of an information bearlng surface 7 Or the video disc 5 is shown enlarged within a circle 8.
A plurality of information tracks 9 are formed on the video disc 5. Each track ls formed with successive llght reflective reglons 10 and llght non-reflectlve regions 11. The direction of reading ls lndlcated by an arrow 12. The read beam 4 has two degrees Or movemer.t, the first of which is in the radial direction as lndi-cated by a double headed arrow 13; the second of whi^h ls the tangential direction as indicated by a double headed arro~l 14. The double heads of each of the arr~s 3 13 and 14 lndicate:that the read beam 4 can move in both directions ln each of the radial degree and tan-gentlal degree.
Referrlng to Figure 2, the optical system ccm-prises a lens 15 employed for shaping the beam to fully ~111 an entrance aperture 16 of a microscoplc ob~ect've lens 17. The ob~ec~ive lens is employed for forming the spot 6 of light at its point of lmplngement with the video disc 5. Improved results have been found when the entrance aperture 16 is overfllled ~y the -12- 1~.5~D835 readln~ beam 4. Thls results ln maximum llght lntensity at the spct 6.
After the beam 4 ls properly formed by the lens 15, it passes through a dlrraction grating lB which splits the read beam into three separate beams (not shown). T~o o~ the beams are employed ~or developlng a radial ~racking error and the other is used for develop-ing both a ~ocus error signal and the information signal.
These three oeams are treated identically by the remain-ing portinn o~ the optical system. Therefore, they arecollectively re~erred to as the read beam 4. The output ~or the diffraction grating 18 is applied to a beam splitting prism 20. The axis of the prism 20 is slightly offset rrom the path of the beam 4 for reasons that are explained with reference to the description of the performance of the optical s~stem 2 as it relates to a reflected beam 4'. The transmitted portlon of the beam 4 is applied through a quarter wave plate 22 which prc_ ~Vldes a forty-f~ve degree shift in polarization o~ the li~ht forming the beam 4. The rear beam 4 next impinges upon a fixed mirror 24 which re-directs the read beam 4 to a ~irst articulated mirror 26. The function of the first articulated mirror 26 is to move the light beam in a first degree of motlon which is tangential to the 25 surface ~ the video disc 5.to correct ~or time base error errors introduced into the reading beam 4 because of eccentricities in the manufacture of the dlsc 5.
The tangential direction is in the ~orward and/or back-ward direction of the in~ormation track on the video disc 5 as indicated by the double headed arrow 14. The read beam 4 now impinges upon the entrance aperture 16, as previously described, and ls ~ocused to a spot 6 upon the inrormation bearing track 9 of the video disc 5 by the lens 17.
The first articulated mirror 26 directs the light beam to a second articulated mirror 28. The second articulated mirror 28 is employed as a tracking mirror. It is the runction of the tracklng mirror 28 to respond to tracking error signals so as to slightly ch~nge its physical position to direct the polnt Or impin~ement ~ Or the read beam 4 so as to radlally tracl; the information carrying indicia on the surface of the video disc 5. The second artlculated mirror 28 has one degree of movement which moves the light beam in a radial di-ection over the surface of the vldeo disc 5 or indicated by the double headed arrow 13.
In normal playing mode, the focused beam of light i~pinges upon successively positioned light reflective regions 10 and light non-reflective regions 11 representing the frequency modulated information.
In the preferred embodiment, the light non-reflective regions 11 are light scattering elements carried by the video disc 5. The modulated light beam is a light equivalent of the electrical f~equency modulated signal ccntaining all the recorded information. This modulated light beam is generated by the microscopic objective lens 17 by gathering as much reflected light from the ~ successively positioned light reflective region 10 and light non-reflective regions 11 on the video disc 5. The re~lected portion of the read beam is indicated at 4'. The reflected read beam 4' retraces the same path previously explained by impinging ir. sequence upon the second articulated mirror 28, the first arti-culated mirror 26, and the fixed mirror 24. The re-flected read beam 4' next passes through the quarter-wave plate 22. The quarterwave plate 22 provides an additional forty-five degree polarization shift re-sulting in a total of ninety degrees in shift of polar-lzation to the reflected read beam 4'. me reflectedread beam 4' now impinges upon the beam splitting prism 20, which prism dlverts the reflected read beam 4' to impinge up~n a signal recovery subsystem lndicated generally at 30.
3~ The function of the beam splittlng prism is to prevent the total reflected read be~m ~' from re-entering the laser 3. The effect of the returning read beam 4' upon the laser 3 would be to upset the mechanism whereby the laser oscillates ln lts predetermined mcde -14- 1 ~ ~ 8 3 S
of operation. ~ccordingly, the beam splittlng prlsm 20 redirects a significant portion of the reflected read beam 4' for preventing feedback into the laser 3 when the laser 3 would be affected by this feedback portion of the reflected read beam 4'. For those solld state lasers which are unaffected by the feedback of the re-flected llght beam 4', the beam splitting prism 20 is unnecessary. The solid state laser 3 can function as the photo detector portion of the slgnal recovery sub-system 30 to be described hereinafter.
Referring to Figure 1, the normal operatingmode of the sigllal recovery subsystem 30 is to provide a plurality of informational signals to the remaining portion of the player 1. These informational signals fall generally into two types, an informational signal itself ~hich represents the stored information. A
second type of signal is a control signal derived from the informational signal for controlling various por-~ tions of the player. The informational signal is a frequency modulated signal representing the lnformation stored on the video disc 5. This informatlonal signal is applied to an FM processing subsystem indicated at 32 over a line 34. A first contrpl signal generated by the signal recovery subsystem 30 is a differentlal focus error signal applied to a focus servo su~system lndica-ted at 3~ over a line 38. A second type of control signal generated by the signal recovery subsystem 30 is a differential tracklng error signal applied to a track-ing servo subsystem 4~ over a line 42. The differential 3Q tracking error signal from the signal recovery sub-system 30 is also applied to a stop motion subsystem indicated at 44 over the line 42 and a second line 46.
Upon receipt of the START pulse generated in a function generator 47, the rirst runction of the video disc player 1 is to activate the laser 3, actlvate a spindle motor 48, causlng an integrally attached spindle 49 and its video disc member 5 mounted thereon to begin spinning. The speed of rotation of the splndle 49, as provlded by the splndle motor 48, is under the ;

1 1 ~ 3 5 control Or a spindle servo subsystem 50. A splndle tachometer (not shown) ls mounted relative to the spindle 4~ to generate electrical signals showing the present speed of rotation of the spindle 49. The tachometer comprises two elements which are located one hundred eighty degrees apart with reference to the spindle 49. Each of these tac`nometer elements generates an output pulse as is common in the art. Because they are located one hundred eighty degrees out of phase with each other, the electrical slgnals generated by each are one hundred eighty degrees out of phase with each other. A line 51 carries the sequence o~ pulses gener-ated by the first tachometer elements to the spindle servo subsystem ~0. A llne 52 carries the tachometer pulses from the second tachometer element to the spindle servo subsystem 50. ~er the spindle servo subsystem 50 reaches its predetermined rotational velocity of 1799.1 revolut~ons per minute, lt generates a player enable ~ signal on a line 54. The accurate rotational speed Or 1799.1 revolutions per minute allo~s 30 frames Or television lnformation to be displayed on a standard televlslon receiver.
The next major functioning ~ the vldeo dlsc player 1 ls the actlvatlon of a carrlage servo sub-system 55. As previously mentloned, the reading of thefrequency modulated encoded lnformatlon from the vldeo dlsc 5 is achieved by dlrecting and focuslng a read beam 4 to lmpinge upon the successlvely posltloned light reflectlve reglon 10 and a llght non-reflective reglon 11 3 on the vid~ dlsc 5. For optlmum results, the read beam 4 should impinge upon the plane carryln~ the encoded lnformation at rlght angles. To achieve thls geometric conflguration requlres relative movement between the comblned ~tlcal system 2 and the video dlsc 5. Elther the video disc 5 can move under the fixed laser read beam 4 or the optical system 2 c~n move relative to tne fixed vldeo disc 5. In this embodiment, the optlcal system 2 is held statlonary and the vldeo dlsc 5 ls moved under the readlng beam 4. The carrlage servo ~150835 subsystem controls thls relative movement between the video disc 5 and the optical system 2.
As com~letely descrlbed hereinafter, the carriage servo subsystem adds a degree of flexibility to the overall functionlng of the video disc player 1 by directing the aforementioned relative movement in a number of different modes of operation. In its first mode of operation the carriage servo subsystem 55 re-sponds to the player enable signal applied to it over the line 54 to move a carriage assembly 56 such that the read beam 4 impinges upon the video disc 5 perpendi-cular to the information bearing surface of the video disc 5. At this time it would be important to note that the term carriage assembly is used to identify the structural member upon which the video disc ls carried.
This also includes the spindle motor 48, the spindle 49, the spindle tachometer (not shown) a carriage motor 57 and a carriage tachometer generator 58. For the purpose ~ of not unduly complicating the broad block diagram shown in Figure 1, the carriage assembly is not shown in great detail. For an understanding of the summarized opera-tion of a video disc player, it is important to note at this time that the function of the carriage servo subsystem is to move the carriage to its inltial posi-tion at which the remaining player functions will beinltiated in sequence. Obviously, the carriage servo subsyste~ can position the carriage at any number of fixed locations relative to the video disc pursuant to the design requirements of the system, but for the purposes ~ this description the carriage is positioned at the beginning of the frequency modulated encoded informatlon carrled by the video disc. The carriage motor 57 provides the driving force to move the carriage assembly 56. The carriage tachometer generator 58 is a current source for generatlilg a current indicating the lnstantaneous speed and direction ~f movement of the carriage assembly.
The spindle servo subsystem 50 ha9 brought the spindle speed up to its operational rotational rate of !

17~g.1 rpm at ~hich time the player ena~le slgnal ls generated on the line 54. The player enable signal on the llne 54 is applied to the carriage servo subsystem 55~for controlling the relative motion between the carriage assembly 56 and the optional system 2. The next sequence in the PLAY operation is for the focus servo subsystem 36 to control the movement of the lens 17 relative to the video disc 5. me focusing opera-tion includes a coil, (not shown), moving the lens 17 under the direction of a plurality of separate elec-trical waveforms which are summed within the coil itself.
These waveforms are completely described ~:ith reference to the descrlption ~iven for the focus servo subsystem in Fi3ures 6a, 6b and 6c. A voice coil arrangement as found in a standard loud speaker has been found to be suitable for controlling the up and down motion of the lens 17 relative to the video disc 5. The electrical signals for controllil~ the voice coil are generated by ~ the focus servo subsystem 36 for application to the coil over a line 64.
Tne inputs to the focus servo subsystem are applied from a plurality of locations. The first of ~hich is applied from the signal recovery subsystem 30 over the line 38 as previously described. The second input signal is from the FM processlng circuit 32 over a line 66. The FM processing subsystem 32 provldes the frequency modulated signal read from the surface of the video disc 5. A third input signal to the focus servo subsystem 36 is the ACQUIRE FOCUS enabling logic signal 30 generated by the act of puttlng the player into lts pla-y mode by selection of a functlon PLAY button wlthin the function generator 47.
The function of the focus servo subsystem 36 is to position the lens 17 at the optimum distance from 35 the video disc 5 such that the lens 17 is able to gather and/or collect the maYimu~. lisht reflected from the video disc 5 and modulated by the successively posi-tioned light reflective region 10 and llght non-reflective region 11. This optimum range is approxi-:

.

:1150835 mately .3 microns in lensth and ls located at a distance cr one micron above the top surface of the video dlsc 5.
The focus servo subsystem 36 has several modes Or oper-ation all of which are descrlbed hereinafter in greater detail with reference to Figures 5, ~a, ~`o 8nd ~c.
At the present time it ls important to note that the focus servo subsystem 36 utilizes its three lnput signals in various combinations to achieve an enhanced focusing arrangement. me differential focus error si~nal from the signal recovery subsystem 30 provides an electrical representation of the relative distance between the lens 17 and the video disc 5. Un-fortunately, the differential focus error signal is relatively small in amplitude and has a ~Jave shape containing a number of positions thereon, each of which indicate that the proper point has been reached. All but one of s-ch positions are not the true optimum focusing positions but rather carry false information.
~ Accordingly, the differential focus error signal itself is not the only signal emplo~Jed to indicate the optimum focus condition. IJhile the use of differential focus error itself can oftentimes result ~nthe selection of the optimum focus position, it cannot do so reliably on every focus attempt. Hence, the combination of the differential focus error signal with the slgnal indica-tive of reading a frequency modulated signal from the video disc 5 provides enhanced operation over the use of using the differentlal focus error signal ltself.
During the focus acquiring mode of operation, 3 the lens 17 ls moving at a relatively high rate of speed towa-ds the video disc 5. An uncontrolled lens detects a frequency modulated signal from the information carried by the video dlsc 5 in a very narrow spaclal range. This very narrow spacial range is the optimum focusing range. AccordinglyJ the combination of the detected frequency modulated si~nal and the differential focus error signal provides a reliable system for ac-quiring focus.
The focus servo subsystem 36 herelnafter ..~

il50835 described contains additional improvements. One of these improvements ls an addition of a rurther fixed signal to those alraady described whicll ~urther helps the rOcus servo subsystem 36 acquire proper focus on the initial attempt to acquire focus. This addi-tional signal is an internally generated kickback slgnal which is initiated at the time when a rrequency modulated signal is detected by the FM processing subsystem 32. This internally generated kickback pulse is combined with the previously discussed signals and applied to the voice coil so as to independently cause the lens to physically move back through the region at llhich a frequency modulated signal was read from the disc 5. This internally generated fixed kic~back pulse signal gives the lens 17 the opportunity to p~ss through the critical optimum focus~n~ point a nu~ber of times during the first transversing of the lens 17 to~lards the video disc 5.
Further improvements are described for handling momentary loss of focus during the play mode of opera-tion caused Dy imperfection in the encoded frequency modulated signal which caused a momentary loss of tne frequency modulated signal as detected by the FM
processing subsystem 32 and applied to the ~ocus servo 25 subsystem 36 over the line 66.
A tangential servo subsystem 80 recelves lts first input signal from the FM processing subsystem 32 over a line 82. The input signal present on the line 82 ls the frequency modulated signal detected from the sur-30 face of the video disc 5 by the lens 17 as amplifled lnthe signal recovery subsystem 30 and applied to the FM
processing subsystem 32 by a line 34. The slgnal on the line 82 is the video signal. The second input signal to the tangential servo subsystem 80 is over a line 84. The 35 signal on the line 84 is a variable DC si~nal generated by a carriage position potentio~neter. ~he amplitude or the variable voltage signal on the line 84 indicates the relative position of the point Or impact Or the reading spot ~ over the radial distance lndicated b~ a double headed arrow 85 as drawn upon the surface of the video disc 5. This variable voltage ad~usts the gain of an internal circuit for ad~usting its operatlng charac-teristlcs to track tlle relative position of the spot as it transverses the radial positlon as lndicated by the length of the line 86.
The function Or the tangential tlme base error correction subsystem 80 ls to ad~ust the signal detected from the video disc 5 for tangential errors caused by eccentricit~ of the information tracks 9 on the dlsc 5 and other errors introduced lnto the detected signal due to any ph~sical imperfection of the video dlsc 5 ltself. The tangential tlme base error correction subs~Jstem 80 performs its func~ion by comparing a signal read from the disc 5 with a locally generated signal.
The difference between the two signals is indicative of the instantaneous error in the slgnal being read by the pla~er 1. More speclally, the signal read from the disc ~ 5 is one whic'll was carefully applied to tne disc with a predetermined amplitude and phase relative to other signals recorded therewlth. For a color televlslon FM
signal this is the color burst portion of the vldeo signal. The locally generated signal is a crystal con-trolled oscillator operating at the color subcarrier frequenc~ of 3.579545 megahert~. The tangential time base error correction subsystem 80 compares the phase difference between the color burst signal and the color subcarrier oscillator frequency and detects any differ-ence. This difference i8 then employed for ad~ustlng the phase ~ the remalning portion of the line of FM
lnformation which contalned the color burst slgnal.
The phase difference of each succeeding llne is gener-ated in exactl~J the same manner for provldlng contlnuous tangential time base error correction for the entire signal read from the dlsc.
In other embodiments storing lnformatlon signals which do not have a portion thereof comparable to a color ~urst signa~ such a~l~ ~ having predeter-mined amplitude and phase relative to the remalning .

115083~ ' si~nals on the disc 5 can be perlodlcally added to the information when recorded on the dlsc 5. In the play mode, thls portion of the recorded lnformation can be selected out and compared witll a locall-y generated 5 slsnal comp~rable to the color subcarrier osclllator.
In this manner, tangential tlme base error correction can be achieved for any signal recorded on a video disc member.
The error signal so detected in the comparison of the slgnal read from the video disc 5 and the inter-nally generated color subcarrier oscillator frequency ~s applied to the first articulated mirror 25 over llnes 88 and 90. The signals on lines 88 and 90 operate to move the first articulated mirror 26 so as to re-direc~ the read beam 4 forward and backwards along thelnformation track, ln the dlrection of the double headed arrow 14, to correct for the time base error lnjected due to an imperfectlon from a manufacture of the video disc 5 and/or the reading therefrom. Another output signal from the tangential time base error cor-rection subsystem 80 is applied to the stop motion sub-system 44 over a line 92. Thls slgnal, as completely described hereinafter, is the composite sync signal which is generated in the subsystem 80 by separating the composite sync signal from the remaining video signal.
It has been found convenient to locate the sync pulse separator in the tangentlal time base error correction subsystem 80. This sync pulse separator could be located in any other portion of the player at a point where the complete video signal is available from the F~ processing subsystem 32.
A ~urther output 5 ignal from the tangential subsyste~ is a motor reference ~requency applied to the spindle servo subsystem 50 over a line 94. The genera-tlon of the motor reference rrequency in the tangentialsubsystem 80 is convenieilt because of the presence of the color subcarrier osclllator frequency used ln the comparison operation as previously described. This color subcarrler oscillator ~requency is an accurately 1~50835 ~
. ~
gellera~ed signal. It ls divided down to a motor refer-ence frequency used in the control Or the spindle se-vo speed. ~- utili~ing the color su~carrier frequency as a control frequenc~r for the speed of the spindle, the speed Or the spindle is effectively loc~ed to this color subcarrier frequency causing the spindle to rotate at t'ne precise frame frequenc~ ra~e required for maximu~, fidelit-~ in the display of the information detected from the video disc 5 on either a televisicn receiver indicated at 95 and/or a TV monitor indica~ed at 98.
The tracking servo subsystem 40 receives a plurallty of input signals, one of whic~l is the pre-viously descri~ed differential tracking error si~nal generated by a signal recovery subsystem 30 as applied thereto over a line 42. A second input signal to the tracking servo subsyste~ ~0 is generated in a function generator 47 over a line 102. For the purpose of clar-ity, the function gellerator 47 is s'no~n as a single block. In the preferred embodiment, the function gener-ator 47 includes a remote control function generatorand a series of switches or buttons permanently mounted on the ^onsole of the video disc player 1. The specific functions so generated are descr~bed in .~ore detail in the detailed description Or the carriage servo sub-system $5 contained hereinafter.
The signal contained on the line 102 is asignal which operates to disable the normal functioning of the tracking servo 40 during certain functi~ns initiated by the function generator 47. For example, the function generator 47 is capable of generatin~ a signal for causing the relative movement of the carriage assembly 56 over the video disc 5 to be in the fast for~ard or fast reYerse condition. By definiticn, the lens is traversing the video disc 5 in a radial direction 3~ as represented by the arrol~ 13, rapidly sklpping over the tracks at the rate of 11,000 tracks per inch and tracking is not expected in this condition. Hence, the signal fro~
the function generator 47 on the line 102 disables the tracking servo 40 so that it does not attempt to operate in i !

835 f lts normal tracking mode.
A third input signal to the tracking servo subsystem 40 is the stop motion compensatlon pulse gene~
ated ln the stop motion subsystem 44 and applied over a line 104. An additlonal lnput slgnal applled to tracklng servo subsystem 40 ls the subsystem loop lnterrupt signal generated by the stop motion subsystem 44 and applied over a llne 10~. A third input si~nal to the tracking servo subsystem 40 is the stop motion pulse generated by the stop motion subsystem 44 and applied o-~er a line 108.
The output slgnals from the tracking servo sub-system 40 include a first radial mirror tracking signal over a line 110 and a second radial mirror control on a line 112. The mirror control signa~ on the line 110 and 112 are applied to the second articulated mlrror 28 which is employed for radial tracking purposes. The control signals on the lin~ 110 and 112 move the second artlculated mirror 28 such that the readlng beam 4 impinging thereupon is moved in the radial direction and ~ becomes centered on the lnformation track 9 illuminated by the ~ocused spot 6.
A further output slgnal from the tracking servo subsystem 40 is applled to an audio processing subsystem 114 over a line 116. The audlo squelch slgnal on the line 116 causes the audio processlng subsystem 114 to stop transmitting audio signals for the ultimate appli-cation to the loud speakers contalned ln the TV receiver 96, and to a pair o~ audio ~acks 117 and 118 respec-3 tively and to an audio accessory block 120. The audio ~acks 117 and 118 are a convenient polnt at which exter-nal equipment can be interconnected with the video disc player 1 for receipt Or two audio channels ~or stereo application.
A further output signal rrom the tracklng servo subsystem 40 is applied to the carriage servo subsystem 5~ over a llne 130. The control signal present on the line 130 ls the DC component ~ the tracking correction signal which ls employed by the carrlage servo subsystem for providing a further carrlage control slgnal lndica-tive of how closely the tracklng servo subsystem 40 is following the directlons glven by the ~unctlon generator 47. For example, lf the function generator 47 glves an lnstruction to the carrlage servo 55 to provlde carriage movement calculated to operate with a slow forward or slow reverse movement, the carriage servo subsystem 55 has a further control signal for determinlng how well it is operatlng so as to cooperate with the electronlc control signals generated to carry out the instruction from the functlon generator 47.
The stop motion subsystem 44 is equlpped with a plurality of input signals one of which ls an output signal of the function generator 47 as applied over a llne 132. The control signal present on the line 132 is a STOP enabling signal indicating that the vldeo disc player 1 should go into a stop motion mode of operation.
A second input signal to the stop motion subsystem 40 ls the frequency modulated sig~l read off ~f the video disc and generated by the FM processing subsystem 32.
The video si~nal from the FM processing subsystem 32 is applied to the stop motion subsystem 44 over a line 134.
Another input signal to the stop motion subsystem 44 is the differential tracking error as detected by the

2~ signal recovery subsystem 30 over the line 46.
The tangential servo system 80 is equipped with a plurality of other output sisnals in additlon to the ones previously identified. The first of which ls applied to the audio processing subsystem 114 over a llne 140. The signal carried by the line 140 ls the color subcarrier oscillator frequency generated in the tanential servo subsystem 80. An additlonal output signal from the tangential servo 80 ls applied to the FM processing subsystem 32 over a llne 142. The signal carrled by the llne 142 ~s tne chroma portion of the video signal generated in the chroma separator fllter portion of the tangential servo subsystem 80. An addi-tional output signal ~rom the tangential servo 80 ls applied to the FM processing subsystem 32 over a line 14''. The signal carried by tlle llne 144 ls a gate enab-ling signal generated by a first gate separator portion of the tangential servo system 80 wlllch l~dicates the installtaneous presence o~ the burst ~ime perlod ln the 5 received video signal.
The focus servo receives its ACQUIRE FOCUS
signal on a line 145.
The power output from the spindle servo sub-system 50 is applied to the spindle motor 48 over a line 14~.
The power generated in the carrlage servo 55 for driving the carriage motor 57 is applied thereto over a line 150. The current generated in the carriage tacnometer generator 58 for application to the carriage 15 servo subsystem 55 indicative of the instantaneous speed and direction of the carriage, is applied to the carriage servo subsystem ~5 over a line 152.
The FM processing unit 32 has an additional pluralit~ of output signals other than those alread-~
described. A first output signal from the FM processingsubsystem 32 is applied to a data and clock recovery subsystem 152 over a line 154. The data and clock re-covery circuit is of standard design and it is employed to read address information contained in a predetermined 25 portion of the information stored in each spiral and/or circle contained on the surface of the video.disc 5.
The address information detected in the video signal furnished by the FM processing unit 32 ls applied to the runction generator 47 from the data and clock recovery subsystem 152 over a line 15~. The clocking lnformation detected by the data and clock recovery subsystem is applied to the function generator over a line 158. An additional output signal from the FM processir.g unit 32 is applied to the audio processing subsystem 114 over a

3~ line 160, The signal carried by the line 160 i8 a fre-quenc~J modulated video signal from the FM distributlon amplifiers contained in the FM processing unit 32. An addltlonal output signal from the ~M processing subs~Jstem 32 ls applled to an ~F modulator 152 over a line 164.

-Tle line 16' carries a video output signal from the Fl;~
detector portion of the FM processing unlt 32 A final output signal from the FM processing unit 32 ls apolied to the TV monitor 98 over a line 155. The llne 166 carries a video signal of the type displayable in a standard TV monito, 98.
The audio processing S~Jstem 114 receives an additio al input signal from the function generator 47 over 2 line 170. The signals carried by the line 170 from the function generator 47 are such as to switch the discriminated audio signals to the various audio accessory systems used herewith. me audio contained in the FM modulated signal recovered rrom the video disc 5 contains a~plurality of separate audio signals.
rlore specificall~, one or two channels of auàio can be contained in the FM modulated signal. These audio channels can be used in a stereo mode Or operation. In one of the preferred modes of operations, each channel contains a dlfferent language explaining the scene shOr~n on the TV receiver 96 and/or TV monitor 98. The si_,nals - contained on the line 170 control the selection at which the audio channel is to be utilized.
The audio processing system 114 is e~uipped with an additional output signal for application to the RF
modulator 162 over a line 172. The signal applied to the R~' modulator 152 over the line 172 is a 4.5 mega-hertz carrier frequenc~J modulated by the audio informa-tion. The modulated 4.5 megahert carrier further modulates a channel rrequency oscillator having its center ~requency selected for use with one channel of the TV receiver. This modulated channel frequency oscillator is applied to a standard TV receiver 96 such that the internal circuitry of the TV recelver demodulates the audio contained in the modulated channel frequency signal in its standard mode of oper-ation.
The audio signals applied to the audio acces-sory unit 120 and tlle audio Jaclcs 117 and 118 lies within the normal audio ran~e suitable for driving a -.

loudspea~er b~I means of the audlo jacks 117 and 118.
The same audio frequencies can be the ir.put to a stereophonic audlo ampllfier when such ls employed as the audio accessory 120.
In the preferred embodiment, the output from the audio processing system 114 modulates the channel 3 frequenc~r oscillatDr before applicaticn to a standard TV receiver 96. l~ile Channel 3 has been convenl-ently selected for thls purpose, t~e oscillating ~re-quency of the channel frequency oscillator can be adapted for use with any channel of the standard TV
receiver 96. The output of the ~F modulator 162 is applied to the TV receiver 96 over a line 174.
An additional output signal frcm the function generator 47 is applied to the carriage servo subsystem 55 over a line 180. The line 180 represents a plural-ity of individ-lal lines. Each indi~idual line is not shc;ln in order to keep the main block diagram as clear as possible. Each o the individual lines, schematic-ally ind~cated by the single line 180, represents an ~ instruction from the function generator instructing the carriage servo to move in a predetermined direction at a predetermined speed. This is described in greater detail when describing the detailed operation of the carriage servo 55.
NORMAL PLAY MODE - SEQUENCE OF OPERATION
The depression of the play button generates a PLAY signal from the function generator followed by an ACQUIRE FOCUS signal. The PLAY signal is applied to ~he laser 3 by a line 3a for generating a read beam 4.
The PLAY signal turns on the spindle motor subsystem 50 and starts the spindle rot~ting. After the spindle servo subsystem accelerates the spindle motor to its proper rotational speed Or 1799.1 revolutions per 3~ minuteJ the sp~ndle servo subsystem 50 generates a PLAYER ENA~LE signal for application to t~e carria~e servo subsystem 55 ror controlling the relative moYe-ment between the carriage assembly and the optical assembly 2. The car~iage servo subsystem 55 directs -2~- 11~835 the ~oveme.~t o~ the carrlage such that the read beam

4 is positioned to impinge UpOIl the beginnlng portion of the inform~tion stored on the video disc record 5.
Once the carri~ge servo subsystem 55 reaches the approx-imate beginning Or the recorded information, the lensl'ocus servo subs~stem 35 auto.~atically ~oves the l~s 17 towards the video disc surface 5. The movement of the lens is calculated to pass the lens through a po~nt at which opvimum focusing is acllieved. The ~ens servo system preferably achieves optimum focus in combina-tion with other control signals generated by reading lnformation recorded on the video disc surface 5. In the preferred embodiment, the lens servo subsystem has a built-in program triggered by information read from the ~isc whereby the lens is caused to move through the optimum focusing point several times by an oscilla-tory type microscopic retracing of the lens path as the lens 17 moves through a single lens focusing acquiring procedure. As the lens moves through the optimum focusi-ng point, it automatically acquires information from the video disc. This information consists of a total Fr~i signal as recorded on the video disc 5 and additionally includes a differential focus error slgn21 and a dirferential tracking error signal. The size of the video information signal read from the disc is used as a feedback signal to tell the lens servo subsystem 36 that the correct point of focus has been success-fully located. ~en the point of optimum focus has been located, the focus servo loop is closed and the 3 mechanically initiated acquire focus procedure ls terminated. The radial tracking mirror 28 is now responding to the differential tracking error generated from the informaticn gathered by the reading lens 17.
The radial tracking error is causin~ the radial track-ing mirror 28 to follow the information track andcorrect for any radial departu~es from a perrect spiral or circle track configuration. Electronic processing of the detected video Fl~ signal generates a tangential error signal which is applied to the tangential ~lrror for correctin~ phase error in the readins process caused by small physical deformaties in the surface Or the video disc 5. During the normal play mode, the servo subsystems hereinbefore described continue their normal mode of operation to maintaln tlle read beam 4 properly in the center of the information track and to maintail~ the lens at the optimum focusing point such that the light gathered by the lens generates a high quality si~nal for display on a standard television receiver cr in a television monitor.
The frequenc~J modulated signal read from the disc needs additional processing to achieve optimum fideli'y durin~ the display in the television receiver 9~ and/or television monitor 98.
Immediately upon recovery from the video dlsc surface, the frequency modulated video signal is applied to a tangent~al servo subsystem 80 for detecting any phase difference ~resent in the recovered video signal and caused by the mechanics of the reading process.
The detected phase difference is employed for driving a tangential mirror 26 and ad~usting for this phase dlfference. The movement of the tangential mlrror 26 functions for changing the phase of the recovered video signal and eliminatlng time base errors lntro-duced into the reading process. The recovered videosi~nal is F~ corrected for achieving an equal amplitude FM signal over the entire FM video spectra. This re-quires a variable amplification of the FM signal over t~le FM video spec~ra to correct for the mean transfer function of the readin~ lens 17. More speclfically, the high frequency end of the video spectrum is atten-uated more b~y the reading lens than the lo~ frequency portion of the frequency scectrum of the frequency modulated signal read from the video disc. This equaiization ls achieved throu~h amplif~vring the higher freauency portion more than the lc-~ler freque!~cy por-tion. After the frequency modulation correction is achieved, the detected si~nal is sent to a discrimina-tor board whereby the discrimillated video is produced "

for application to the remainillg portions of the board.
Referring to Figure 3, there is shown a gen-erali-ed block dlagram of the spindle servo subsystem indicated ai 50. One o~ the functlons of the splndle servo subsystem is to maintain the speed of rotation of the spindle 49 by the spindle motor 48 at a constant speed of 1799.1 rpm. Obv1ously, this figure has been selected to be compatible with the scanning rrequency Or a standard television receiver. The standard tele-vision receive, receives 30 frames per second and thelnformation is recorded on the video disc such that one complete fra.~e of television informaticn is con-tained in one spiral and/or track. Obviously, when the time requirements of a televis ion receiver or tele-vision moritcr differ from this standard, then thefunction of the spindle servo subsyste~ 1s to maintain the rotational speed at the new stand~rd.
The function gerRrator 47 provides a START
pulse to the spindle motor. As the motor begins to turn, the tachometer input sig~l pulse train ~rom the flrs~ tachometer element is applied to a Schmitt trig-ger 200 over t'ne line 51. The tacho~.eter lnput signal pulse train from the second tachometer element is applied to a second Schmitt trigger 202 over the line 25 52. A 9.33 KHz motor reference frequency is applied to a third Schmitt trigger 204 from the tangential servo subsystem 80 over a line 94.
The output from the Schmitt trigger 200 is applied to an edge generator clrcuit 206 through a 30 divide by t~o network 208. The output rrcm the Schmitt tri2ger 202 is applied to an edge generator 210 through a divided by two network 212. TJle output from the Schmitt trigger 204 ls applied to an edge generator circuit 214 througll a divided by two networl{ 216. Each 35 of the edge generators 20~, 210 and 214 is employed for ger.erating a sharp pulse corres~ondlng to both tho positive going edge and the negati~e going edge of the signal applied respectivel~ rro~ the divided by two net~orks 208, 212 and 215.

-:

` ` ~15083g ~1 The output from tlle edge generator 214 lsapplied ~s the reference phase si~nal to a flrst ph~3e detector 21~ and to a second phase detector 220. The phase detector 218 has as lts second input signal the output from the edge generator 206. The phase genera-tor 220 has as its second input signal the output of the edge generator 210. The phase detectors operate to indicate any phase difference between the tachometer lnput signals and the motor reference frequency. The output from the phase detector 218 is applied to a summation circuit 222. And the output from the phase detector 220 is also applied as a second input to the summation circuit 222. The output from the summation circuit 222 is applied to a lock detector 224 and to a po~1er amplifier 225. The function of the lock detecto~
224 is to indicate when the spindle speed has reached a predetermined rotational speed. This can be done by sensing the output signals from the summation circuit 222.
I;~ the preferred embodiment is has been deter-mined that the rotational speed of the spindle motor should reach a predetermined speed before the carriage assembly is placed in motion. When a video disc is brou~ht to a relatively high rDtational speed, the disc rides on a cushion of alr and rises slightly vertical against the force of gravity. Additionally, the centrifu~al force of the video disc causes the video disc to somewhat flatten considerably. It has been found that the vertical movement against gravity caused by the disc riding on a cushion of air and the vertical rise caused by the centrifugal force both lift the video disc from its position at rest to a stabillzed positlon spaced from its initi~l rest posi-tion and at a predetermined position with reference to other internal fixed members of the video disc player cabinet. The dynamics ol' a sp nnins disc at 1799.1 rpm witll a predetermined weight and density can be calculated such as to insure that the disc is spaced from all internal components and is not in liS0835 , ~
contact l~ith an~J such lnternal components. Any con-tact between the disc and the player cabinet causes rubbing, and the ru~bing causes damage to the video disc through abrasion.
In the preferred embodiment, the lock detector 224 h~s been set to generate a PLAYER ENAELE pulse on the line 54 when the spindle speed is up to its full 1799.1 rpm speed. A speed less than the full rota-tional speed can be selected as the point at which the player enable signal is generated provided that the video disc has moved sufficiently from its lnitial position and has attained a position spaced from the internal components Or the video disc player cabinet.
In an alternate embodiment, a fixed delay, after appl~T-lng the START signal to the sp~ndle motor, ls used tostart the carriage assembly in motion.
During the normal operating mode o~ the video disc p'ayer lj th~e tachometer input signals are con-tinuously applied to the Schmitt trig~ers 200 and 202 over the lines 51 and 52, respectively. These actual tachometer input signals are compared against the moto-reference signal and any deviation therefrom is detected in the summation clrcuit 222 for application to the pol,~er amplifier 226. The power amplifler 226 provides the driving force to the spindle motor 48 to maintain the required rotational speed of the spindle 49.
Referring to Figure 4, there is shown a sche-matic blcck diagram Or the carriage servo subsystem 55.
The carriage servo subsystem 55 comprises a plurality Or current sources 230 through 235. The function of each of these current sources ls to provude a predeter-mined value of current ln response to an input signal from the function generator 47 over the line 180. It was previously described that the line 180, shown with rererence to ~igure 1, comprlses a plurallty of in-di~idual llnes. For the purpose~ o~ this description, each of these lines will be identifled as l&Oa through 180e. The outputs of the current sources 230 through 235 are applied to a summation circuit 238. The OUIpUt from the summation circuit 238 ls applied to a p^wer amplirier 240 over a linc 242. Th~ output ~rom the power ampli ier 240 ls applied to the carriage motor 57 over the line 150. A dashed line 244 extending between the carriage motor 57 and the carriage tachometer member 58 lndicates that these units are mechanically connected. The output ~rom the carriage tachometer 58 is applied to the summation circuit by the line 152.
The STAF~T pulse is applied to the current so~rce 232a over a line 180al. The current source 232a functions to provide a predetermined current for moving the carriage assembly from its initial rest position to the desired start of track position. As previously mentioned, the carriage assembly 55 and the optical system 2 are moved relative one to the other. In the standard PLA~' mode Or operation~ the optical system 2 and carriage assembly 55 are moved such that the read beam 4 rrom t~e laser 3 is caused to impinge UpOIl the ~ start o~ the recorded information. Accordingly, the current source 232 generates the current for appllca-tion to the sum~ation circuit 238. The summ2tion circuit 238 runctions to sense the several incremental amounts of current being generated by the ~arious current sources 230 through 235 and compares this sum Or the currents against the current being fed into the summation circuit 238 from the carriage tachometer system 58 over the line 152. It has been previously mentloned that the current generated by the carria~e tachometer 58 indicates the instantaneous speed and posl~ion of the carriage assembly 55. This current on the line 152 is compared with the currents being generated by the current sources 230 through 235 and the resulting dirference current is applled to the po~ler ampli~ier 240 over the line 242 rOr generating the po~er required to move the carriage motor 5~ to the desircd loc2tion.
Only ror purposes Or example~ the carriage tachometer 58 could be generatil~ a r.egative current indicating tllat the carriage assembly 56 is positioned .

. 1150835 ``

at a first location. The current source 232a would generate a secon~ current indicatil~ the desired posi-tion for the carriage assembly 56 to reach ror start-up time. The summation circuit 23~ co~pares the two currents and generates a resultin~ difference current on the line 242 for application to the po~r a~plifier 240. The output from the amplifier 240 is applied to the carriage motor 57 for driving the carriage motor and moving the carriage assembly to the indicated position. As the carrlage motor 57 moves, the carriage tachometer 58 also moves as indicated by the mechanical linkage sho~ln by the line 244. As its posi~ion changes, the carriage tac'nometer 58 generates a nell and differ-ent sig~al on tlle line 152. When the carriage tachom-eter 58 indicates that it is at the same position asindicated b~T the output signal from the current source 232a, the summation circuit 238 lndicates a CO~iPARE
EQUAL co~dition. No signal is applied to the po~er amplifier 2~0 ar!d no additional power is applied to the carriage motor 57 causing the carriage motor 57 ~o stop.
The START signal on t'ne line 180al causes the carriage motor 57 to move to its START position. When the spindle servo subs~Jstem 50 has brought the speed of rotation of the spindle 49 up to its reading speed, a PLAY ENA~L~ signal is generated by the spi~dle servo subsystem ~0 for application to a current source 230 over a line 54. The current source 230 generates a constant bias current sufficient to move the carriage assembly 56 a distance of 1.6 microns for each revolu-tion of the disc. This bias current is applied to the summation circuit 238 for providing a constant current input signal to the poi~er amplifier for driving the carriage motor 57 at the indicated dist~nce per revo-3~ lution. This constant lnput bias currer.t f'~cm thecurrent source 230 is f~ur~her ideni;ifled as a first fixed bias control signal to the carriage motor 57.
The current source 231 receives a FAST FORltARD
E~JA~LE signal from the runcticn generator ~7 over the -~5 line lS~`~. The ~ast rorw.~rd current source 231 gener-ates an outpu' currer.t signal for applicati3n to the summation circuil 23~ and the po~Yer ampli~ier 240 for a~tivating the carriage motor 57 to move the carriage assembly 5~ in the fast forl~ard direction. For clari-fication, the directions referred to in this section Or the description refer to the relative movement of t`.^e carriage assembly and the reading beam 4. These movements are directed generally in a radial direction as indicated by the double headed arrow 13 sh~wn in Figure 1. In the rast forward mode of operation, the video disc 5 is rotating at a very hiEh rot~tlonal speed and hence the radial tracking dces not occur in a straight llne across the tracks as indicated by the double arrow 13. More specifically, the carriage servo subsystem is capable of providing relative motion between the carriage assembly and the optical system 2 such as to traverse the typically four inch wide band of lnfcrmatio:l bearing surface ~ the video disc 5 in approximately four seconds from the outer periphery to the inner periphery. The average speed is one inch per second. During the four second period, the reading head moves across appro~imately forth-four thousand tracks. The video disc is revolving at nearly thirty revolutions per second and hence, under idealized con-ditions, t'ne video disc 5 rotates one hundred and t~1enty times while the carriage servo subsystem 55 provides the relative motion from the outer perlphery to the inner periphery. Hence, the absolute point of 3o impact of the reading beam upon the rotating video disc is a spirally shaped line having one hundred and t~enty spirals. The net effect Or this movement is a radial movement of the point of impingement of the reading beam 4 ~ith the video disc 5 in a radial direction as indicated by a double headed line 13.
The current source 23, rece-lves it~ ~A~ RE-VERSE E~BLE signal from the function generator 47 over the llne 180c. The fast reverse current source 233 pr~-vides its output directly to the summation circuit 238.

The current source 234 is a SLOW FORWARD cur-rent source and receives its SLOW FORWARD ENABLE input signal from the function generator 47 over a line 180d.
The output signal from the slow forward current source 234 is applied to the summation circuit 238 through an adjustable potentiometer circuit 246. The function of the adjustable potentiometer circuit 246 is to vary the output from the slow forward current source 234 so as to select any speed in the slow forward direction.
The current source 235 is a SLOW REVERSE cur-rent source which receives its SLOW REVERSE ENABLE
signal from the function generator 47 over the line 180e. The output from the slow forward current source 235 is applied to the summation circuit 238 through an adjustable potentiometer circuit 248. The adjust-able potentiometer circuit 248 functions in a similar manner with the circuit 246 to adjust the output signal from the slow reverse current source 235 such that the carriage servo subsystem 55 moves the carriage assembly 56 at any speed in the slow reverse direction.
The DC component of the tracking correction signal from the tracking servo subsystem 40 is applied to the summation circuit 238 over the line 130. The function of this DC component of the tracking correc-tion signal is to initiate carriage assembly movement when the tracking errors are in a permanent off-tracking situation such that the carriage servo sub-system should provide relative motion to bring the relative position of the video disc 5 and the read beam 4 back within the range of the tracking capability of the tracking mirrors. The DC component indicates that the tracking mirrors have assumed a position for a substantial period of time which indicates that they are attempting to acquire tracking and have been unable to do so.
CARRIAGE SERVO - NORMAL MODE OF OPERATION
The carriage servo sybsystem 55 is the means for controlling the relative movement between the carriage assembly on which the video disc 5 is located and the optical system in which the reading laser 3 is located. A carrige tachometer is mechanically linked to the carriage motor and operates as a means for generating a highly accurate current value representing the instantaneous speed and direction of the movement of the carriage assembly 56.
A plurality of individually activated and variable level current sources are employed as means for generating signals for directing the direction and speed of movement of the carriage assembly. A first current source for controlling the direction of the carriage motor generates a continuous reference current for controlling the radial tracking of the read beam relative to the video disc as the read beam radially trakcs from the outer periphery to the inner periphery in the normal mode of operation. A second current source operates as a means for generating a current of the same bu. greater amplitude to direct the carriage assembly to move at a higher rate of speed in the same direction as the bias current. This second type of current ceases to operate when the carriage assembly reaches its predetermined position.
An additional current source is available for generating a current value of opposite polarity when compared with the permanently available bias current for causing the carriage motor to move in a direction opposite to that direction moving under the influence of the permanently available bias current.
A summation circuit is employed for summing the currents available from the plurality of current sources for generating a signal for giving directions to the carriage motor. The summation circuit also sums the output current from the carriage tachometer indi-cating the instantaneous speed and location of the carriage assembly as the carriage assembly move pur-suant to the various commands from the input current generators. The summation circuit provides a differ-ence output signal to a power amplifier for generating the power required to move the carriage assembly such t~at the current ~enerated in the carrla~e tachometer ~atches the current generated from input current sources~
Rererring collectively to Figure 5 and Figures oA through 6F, there is shown and described a schematic block dia~ram of the focus servo subsystem 36~ a plur-ality of d~fferent waveforms which are employed with the focus servo subsystem and a plurality of single logic diagrams showing the sequence of steps used in 10 the focus servo to operate in a plurality of different modes of operation. The focus error signal from the signal recovery subsystem 30 is applied to an amplifier and loop compensation circuit 250 over the line 38.
The output fro~the amplifier and loop co~pensation cir-suit 250 is applied to a kiclcback pulse generator 252over a line 254 and to a rOcus servo loop s~litch 256 over the line 254 and a second line 258. The output from the klckback pulse generator 252 ls applled to a drlver circuit 260 over a line 202. The output from the focus servc loop swltch 25~ is applied to the - driver circuit 260 over a llne 264.
The FM video signal is applied from the dls-tributlon amplifier portion of the FM processing sub-system 32 to a FM level detector 270 over the line 66. The output from the FM level detector 270 is ap-plied to an acquire focus loglc circuit 272 over line 274. The output of the FM level detector 270 is ap-plied as a second alternative input signal to the gener-ator 252 over a line 275. The output from the acquire focus logic circult i5 applied to the focus servo loop swltch 256 over a llne 276. A second output signal from the acquire focus logic circuit 272 is applied to a ramp generator circult 278 over a line 280. me acquire focus logic clrcult 272 has as its second input slgnal the acquire focus enable slgnal generated by the function ~enerator 1,7 over the llne 1)'6. m e output of the ra~p generator 278 is applled to t~le driver circuit 260 over a line 281.
The acquire focus enable si~nal applied to the acquire focus lo~ic 272 over tlle line 14~ is shown o..line A of Figure 6A. Easicall~, this sirnal ls a tl~o-level sigial generated by the function generator 47 and havil~ a disabling lo~ler condltion indicated at _82 and an enabling condition indicated ger.~rally at 2&~. The function generator produces this pulse when the video disc player 1 is in one Or its play modes and it is neccssary to read the information stored on the video disc 5.
Rererring to llne ~ of Figure 5A, there is shol~1n a typical ramping voltage waveform generated by the ramp generator circuit 278. During the period of time correspondin~ to the disabling portion 282 of the acquire focus signal, the focus ramp waveform is in a quiescent condition. Coincidental ~ith the turning on of the acquire focus enable si~nal, the ramp generator 27~ generates its rampin~ voltage waveform shown as a sa.qtooth type output waveform going frcm a higher position at 286 to a lower position at 288. This is sholn as a linearly cnanging signal and has been found ~ to be the most useful waveform for this purpose.
Referring to line C of Figure 6A, there is shown a representation of the motion of the lens itself during a number of operatlng modes of the video disc 25 player. Prior to the generation of the acquire focus enabie signal, the lens is generally in a retracted position indicated generally at 290. Upon the receipt of the acquire focus enable signal, the lengs begins to move ln a path indicated by the dash/dot line 292.
30 The dash/dot line 292 begins at a point identified as the upper limit Or lens travel and moves through an intersection with a dotted line 294. This point of intersection is identified as the lens in focus posi-tion 293. lJhen focus is not acquired on the first 35 attempt, the lens continues along the dash/dot line 292 to a p~int 295 ident ~ie~ ~s lo~er limit of lens travel. Ilhen the lens reaches point 295, the lens remains at the lo-wer limit cr lens travel through the portinn of the line indicated generally at 296. The ~ o 1150835 lens continues to follow the dash/dot line to a point indicated at 297 identlfled as the RAMP R~SET polnt.
Th~s ls also sho~n on line A as 28&. Du.ing the ramp reset t~e the lens is drawn back to the upper limit of lens travel portion Or the waveform as indicated at 298.
In this flrst mode of operation the lens falls ln its first attempt at acquiring focus. Tne lens passes throu6h the lens in ~ocus posit~on as indicated by the dotte~ line 294. After failing to acquire focus, the le~s then moves all the way to its lower limit of lens travel at 296 before retracting to its upper limit of lens travel indicated at 298. The upper limit of lens travel position and the lower limit of lens travel position are sensed by limit switches in the lens driver su~assembly not shown.
During a successful attempt to acquire focus, the path of lens tra~el changes to the dotted line indicated at 294 and remains there until focus is lost.
The lens is r.ormally one micron above the video disc 5 when in the focus position. Also, the in-focus posi-tion can var~J over a range of 0.3 microns.
The output signal from the ramp generator 278 to the driver 250 on the line 281 has the configuration sho~Jn on line ~ of Figure 6A.
The ~aveform shown on line G of Figure 6A
shows the wave shape of the signal applied to the FM
level detector 270 over the line 66. The ~aveform shown on llne G ~llustrates two principal conditions. The open double sided sharp pulse indicated generally at 300 is generated by the signal recovery subsystem 30 as the lens passes through focus. This is shown by the vertical line 301 connecting the top o~ the pulse 300 with the point on llne 292 indicating that the lens has passed through the in-focus position as indicated by its intersection with the dotted line 294. Correspond-ing to the description previously given ~lith reference to line C of Figure 6A, the lens passes through focus and the sharp pulse retracts to its no activlty level indlcated generally at 302.

llS083 --4 i-In the second illustration the waveform shownon line G cr Figure 6A illustrates the output from the F~i distri~ution amplifier on the line 56 when the lens acquires focus. This is indicated by the envelope generally represented by the crossed hatched sections between lines 304 and 306.
Referrillg to the waveform shown on line H of Figure 6A there is shown a dash/dot line 3G8 repre-senting the output from the FM level detector 270 corres-ponding to that situation when the lens does not acquirerOcus in its first pass through the lens in focus posi-tion b~ line 294 of line C of Figure 6~.. The output of the level detector represented by the dotted line 311 shows the loss of the FM signal by the detector 270.
The solid line 312 shows the presence of an FM signal detected by the FM level detector when the lens ac-quires focus. The continuing portion of the waveform at 312 indicates that a FM signal is available ln the focus servo subsystem 35.
Referring to line I of Figure 6A there is ~ sho;~n the output char~cteristic Or the focus servo loop switch 255. In the portion of its cperating character-istics generall~J indicated by the portion of the line indicated at 314 the switch is in the off condition representing the unfocused condition. The position of the line 316 represents the focused condition. The vertical transition at 318 indicates the time at which focus is acquired. The operating mode Or the video disc player ~uring the critical period of acquiring focus is more full~ described with reference to the waveforms shown in Figure 6C. Line A of Figure 6C
represents a corrected d~fferential focus error gener-ated by the signal recovery system 30 as the lens follows its physical path as previously descri~ed with reference to line C Or Figure SA. At point 319 of the ~aveform A shown in ~igure 5C the di-fe~ential rOcus error corresponds to a portivn of the lens travel during which no focus errors are available. At the region indicated at 320 the rirst false in-focus error signal . 1150835 is available. There is r~rst a momentary rise in focus error to a first maximum initial level at point 322.
At point 3?2, the differential rOcus error begins to rise in the opposlte direction until it peaks at a point 324. The difrerential focus error begins to drop to a second but opposite maximum at a point 325. At a point 328, halfway between the points 324 and 325, is the optimum in-focus position for the lens. At this point 328, the lens gathers maximum reflected li~ht from the video disc surface. Continuing past point 326, the differential focus error begins to fall towards ~
second false in-focus condition represented at this point 330. The differential focus error rises past the in-focus position to a lower maximum at 332 prior to ralling back to the position at 333 where no focus error information is available. No focus error in-formation is available because the lens is so close to the video disc surface as to be unable to distinguish a difrerence of the diffused illumination presently bathing the two focus detectors.
Referring to line P, there ls shown a waveform representing the frequency modulated signal detected from the video disc surface 5 tl~rough the lens 17 as the lens is moving towards the video disc 5 ln an attempt to acquire focus. It should be noted that the frequency modulated signal from the video disc 5 is detected only over a small distance as the lens reaches optimum focus, and then passes tllrough optimum rOcus.
This small distance is represented by ,sha~p peaks 334a and 334b of the FM detected video as the lens 17 moves through this prererred in-focus position l~hen focus is missed.
l~hlle rOcus can be achieved using only the di~ferential focus error signal shown with reference to llne A Or Figure 6C, one embodiment Or the present inventic~ utili2es the differen~ial rccus error signal as shown on line A of Figure 6C in combination with the signal shown on line ~ of Figure 6C to achieve more reliable acquisition Or focus during each attempt at .. . . . _ .. .

rOCUS .
Figure C o~ line 6C shows an inverted ideal-i ed focus error signal. This idealized error signal is then di~ferentiated and the results shown on line D
Or Figure 6C. The di~ferentiation Or the idealized focus error signal is represented by the line 339.
Small portions o~ this line 339 sho~n at 340 and 342 lying above the zero point indicated at 344 give false indication of proper focusing regions. The reglon 345 falling under the line 339 and above the zero ccndition represented by the line 344 indicates the ran~e within which the lens should be positioned to obtain proper and optimum ~ocus. The re~ion 346 repre-sents approximately 0.3 microns Or lens travel and corresponds to the receipt Or an FM input to the FM
level detector as shown ln llne ~. It should be noted that no Fl~i is shown on line P correspondlng to regions 340 and 342. Hence~ the FM pulse shown on llne ~ is used as a gating signal to indicate when the lens has `oeen positioned at the proper distance above the video disc 5 at which it can be expected to acquire focus.
The signal representing the differentiation Or the idealized focus error is applled to the gener-ator 252 ror activating the ~enerator 252 to generate its kickback waveform. The output from the FM level detector 270 ls an alternative input to the kickback generator for generatlng the ki~lcback waverorm ~or application to the driver 260.
Referrlng back to line ~ of Fl~ure 6A and contlnuing the descrlptlon o~ the waveform shown there-on, the dot/dash portlon beglnning at 285 represents the start o~ the output signal from the ramp generator 27~ for moving the lens through the optimum focusing range. This is a sawtooth signal and lt is calculated to move the lens sn~oothly through the point at which FM ls detected by the FM level detector 270 as lndi-cated by the wave~orm on line H. I~ a flrst mode of operation, the rOcus ramp follows a dot-dash portion s .. .. . . ..... . . .

114~835 ~-3l Or the waverorm to a p~int 287a corresponding to the ti~e at which the output of the F~I level detector sho.;s t'le acquisition of ~ocus by ~enerating the slsnal level at 312a in line II. The output si6nal from the acquire ~ocus logic bloclc 272 turns Or~ the ramp gen-erator ov~r the line 280 indicatin~ that ~ccus has been acquired. l~en ~ocus is acquired, the output from the ramp ~enerator follows the dash line porticn at 287 indicating that focus has been acquired.
Re~erring to line A of Figure 6E, a portion of the focus ramp is shown extending between a first upper ~oltage at 285 and a second lower voltage at 288. The optimum focus point is located at 287a and corresponds with the peak of the FM signal applied to the FM
level detector 270 as shown on line C of F~ure 6~.
Line P is a simplified version of the lens position trans~er functior 290 as shown more specifically with reference to line C of Figure 6A. The lens position trans~er function line 290 extends between an u?per limlt of lens travel indicated at point 292 and a lower limit of lens travel indicated at point 255. The optimum lens focus position is indicated by a line 295.
The optimum lens ~ocus point is therefore located at 299.
Referring to line D of Figure 6~, there is shown the superimposing of a kickback sawtooth wave-form indicated generally ln the area 300 upon the lens position transfer line 292. This indicates that in the top portion of the three kickback pulses are located at 30 302, 304 and 306. The lower portion of the three kickback pulses are located at 308, 310 and 312, re-- spectively. The line 296 again shows the point of optimum focus. The intersection of the line 296 with the line 292 at points 296a, 296b, 296c and 296d shows that the lens itself passes through the optimum lens focus position a plurality of times during one acquire focus enable runction.
Referrin~ to lir.e E of Figure 6P, the input to the FM level detector indicates that durin~ an r:

1150~335 oscillatcr~ motlon of the lens through the optimum focus position as shown by the combined lens travel function characteristic shown in Figure D, the lens has the opportunity to acquire rOcus o~ t~.e F~. signal at four locations indicated at the peaks o~ waveforms 314, 316, 318 and 320.
The waveforms sho~wn with reference to Figure

5~ demonstrate that the addi~ion of a high frequency oscillating sawtooth kickback pulse upon the ramping signal generated by the ramp generator 278 causes the lens to pass through the optimum lens focus position a plurality Or times for each attempt at acquiring lens focus. This improves the reliability of achieving proper lens focus during each attempt.
The focus servo system employed ln the present invention functions to position the lens at the place calculated to provide optimum focusing of the reflected read spot arter impinging upon the information track.
~n a first mode Or operation, the lens servo is moved under a ramp voltage waveform from its retracted position towards its fully dowl~ position. When focus is IlOt acquired during the traverse of this distance, means are provided for automa~ically returning the ramping voltage to its original position and retracing tlle lens to a point corresponding to the start of the ramping voltage. Thereafter, the lens automatlcally g moved through its rocus acquire mode Or operation and through the optimum focus position at which focus is acquired.
In a third mode of operation, the fixed ramp-lng waveform is used in combination with the output from an FM detector to stabllize the mirror at the optimum focus position which corresponds to the point at which a frequency modulated signal is recovered from the informa~ion bearin~ surface of the video dlsc and an output is indica~ed at an Fl~l detector. In a further embodi~ent; an oscillatory waveform is superimposed upon the rampin~ voltage to help the lens acquire proper focus. The oscillatory waveform is tri~gered .

1~50835 by a number of alternatlve input signals. A first such input signal is the output from the ~M detector indicating that the lens has reaclled the optlmum focus point. A second triggering slgnal occurs a flxed tlme after the beginnlng Or the ramp voltage ~aveform. A
third alternatlve lnput signal ls a derivation of the differential tracking err~r indicating the point at which the lens is best calculated to lie within the range at whlch optimum focus can be achieved. In a ~urther embodiment of the present lnvention, the focus servo ls constantly monitoring the presence of FM
in the recovered frequency modulated signal. The focus servo can maintaln the lens in focus even though there is a momentary loss of detected frequency modulated signal. This ls achleved by constantly monltoring the presence of FM slgnal detected from the video disc.
Upon the sensing of a momentary loss of ~re~uenc~T
modulated signal, a timing pulse is generated which is calculated to resta-t the focus acquire mode ~ oper-2~ atlon. However, i~ the frequency modulated signalsare detected prior to the termlnation of this fixed period Or time the pulse terminates and the acquire rOcus mode is skipped. If FM is lost for a period of time longer than this pulse, then the focus acqulre mode is automatically entered. The focus servo con-tinues to attempt to acquire focus until successful acquisltlon is achieved.
FOCUS SERVO SU~SYSTEM - ~ORMAL MODE OF OPERATION
.
The principal function of the focus servo sub-system is to drive the lens mechanism towards the video disc 5 until the ob~ectlve lens 17 acquires optimum focus of the llght modulated slgnal being re~lëcted from the surface of the video dlsc 5. Due to the re-solving power o~ the lens 17, the optlmum focus point ls located approximately one micron from the disc surface. The range of ler.s travel ~t which optimum focus can be achieved is 0.3 microns. The informatlon bearln~ surface of the video disc member 5 upon which the light reflective and light non-reflective members 47~-are positioned, are ~tentimes distorted due to lmper-fectlons in the manufacture Or the video disc 5. The video disc 5 is manufactured accordin~ to standards which l~ill make available ~or use on vldeo disc players those video disc members 5 having errors which can be handled by the focus servo system 36.
In a first mode of operation, the focus servo subsystem 36 responds to an enabling signal telling the lens driver mechanism when to attempt to acquire focus.
A ramp generator is a means ~or generating a ramping voltage for directing the lens to move from its upper retracted position do~n towards the video disc member 5. Unless interrupted by external signals, the ramping voltage continues to move the lens through the optimum focus position to a full lens down position correspond-ing to the end of the ramping voitage. The full lens down position can also be indicated by a limit switc'n which closes ~!hen the lens reaches this position.
~ The lens acquire period equals the time of the ramping voltage. At the end of the ramping voltage peri~d, a~tomatic means are provided for automatically resetting the ramp generator to its initial positic~ at the start of the ramping period. Operator interven-tion is not required to reset the lens to lts lens acquire mode in the preferred embodiment after focus was not achieved during the first attempt at acquir~ng focus.
In the recovery of FM video infor~ation from the video dise surface 5, imperfections on the dlsc surface can cause a momentary loss of the FM signal being recovered. A gating means is provided in the lens servo subsystem 36 for detecting this loss FM
from the recovered FM video signal. This FM detecting means momentaril~ delays the reactivation of the ac-quire focus mode of operation of the lens servo sub-s~Jstem 35 fcr a predeterm1ned time. Duri:;g this pr~-determined time, the reacquisition of the FM si~nal prevents the FM detector means from causing the servo subsystem to restart the acquire focus mode of operation.

1150835 ( In the event that F~ is not detected during this flrst predetermined time, the FM detector means reactivates the ramp generator ror generating the ramping signal which causes tl~e lens to ~ollow through the acquire ~ocus procedure. At the end of the ra~p generator period J the FM detector means provides a further signal for resetting the ramp generator to its initial posltion and to follow through the ramping and acquire rOcus procedure.
In a third embodiment, the ramping voltage generated by the ramp generator has superimpcsed upcn it an oscillatory sequence of pulses. The oscillatory sequence of pulses are added to the standard ramping voltage in response to the sensing of recovered FM
from the video disc sur~ace 5. The combi~tion of the oscillatory waveform upon the standard ramping voltage ls to drive the lens through the optimum focus position in the direction towards the disc a number of times during each acquire ~ocus procedure.
In a further embodiment, the generation of the oscillator~7 waveform is triggered a fixed time after the initiation of the focus ramp si~nal. ~r;1ile this is not as efficient as using the F'l~ level detector output signal as the méans for triggering the oscilla-tory waveform ger.erator it provides reasonable and reliable results.
In a third embodiment, the oscillatory wave-~orm ls triggered by the compensated tracking error 5 ignal.
Referring to Figure 7, there is shown a schematic block dlagram of the slgnal recovery sub-system 30. The waveforms shown in Figure 8, llnes ~, C and D, lllustrate certain o~ the electrical waveforms available within the signal recovery subsystem 30 during the normal operation o~ the player. Referring to Figure 7, the rerlected light beam is indicated at - 4' and is divided into three principal beams. A ~irst beam impinges upon a first tracking photo detector indicated at 380, a second portion Or the read beam 4' s -4~ liS~3 5 ir;pin~es UpOIl a second tracklry~ photo detector 382 and the central inîorrration beam is shown lmplnging upon a concentric rin2 detector lndicated generally at 384.
The concentric ring detector 384 has an inner portion 5 at 38s and an outer portion at 388, respectively.
The output from the first trackin~ photo de-tector 380 is applied to a flrst tracking preamp 390 over a line 392. The output from the second tracking photo detector 382 is applied to a second tracking p reamp 394 over a line 395. The output from the inner portion 386 of the concentric ring detector 384 is applied to a first focus preamp 398 over a line 400.
The output from the outer portion 388 of the concen-tric rin~ detector 3&4 is applied to a second focus pre-amp 402 over a line 404. The output frcm both portlons 386 and 388 of the concentric ring focusing element 384 are applied to a wide band amplifier 405 over a line 405. Al alternative embodiment to tha'c sho~"n would include a summation of the signals on the lines 400 20` and 404 and tlle application of this sum to the wide band amplifier 405. The showing of the line 40~ ls s chematic in nature. The output from the wide band amplifier 405 is the time base error corrected fre-quency modulated signal for application to the FM
processing subsystem 32 over the line 34.
The output from the first focus preamp 398 is applied as one input to a differential amplifier 408 over a line 410. The output from the second focus preamplifier 402 ~orms the second input to the differ-3 ential amplirier 408 over the llne 412. The output from the differential amplifier 408 is the differentlal rOcus error signal applied to the focus servo 36 over the line 38.
The output from the first trackin~ preampli-fier 390 forms one input to a differential amplifier 414 over a line 415 The output fromthe second track-ing preamplifier 394 forms a secor.a inpl;~ to tr-e dlf~e~
ential amplifier 414 over a line 418. The output from the dif.erential amplifie r 414 is a difrerential track--5~- 1150835 in~ error signal applied to the trackin~ servo syste-over the llne 42 and applled to the st~p motlon sub-system over the line 42 and an addltional line 45.
Line A of Fi~ure 8 sllows a cross-sectional view taken in a radial dlrection across a video disc member 5. Light non-re~lective elements are shown at 11 and intertr3ck regions are shown at lOa. Such inte~
track regions lOa are similar in shape to light re-flective elements 10. The ligh~ reflective regions 10 10 are planar in nature and normally are hi~hly polished sur~aces such as a thin aluminum layer. The light no~
reflective regions 11 in the preferred embodiment are light scattering and appear as bumps or elevations above the olanar surface represented by the light re-flective regions 10. The lengths of the line indicatedat 420 and 421 shows the center to center spacing of two adjacently positioned tracks 422 and 423 about a center track 424. A point 425 in the line 420 and a point 42~ in the line 421 represents the crossover point 20` between each of the adjacent tracks 422 and 423 when - leaving the central track 424 respectively. The cross-over points 425 and 425 are each exactly llalfway be-tween the central track 424 and the tracks 422 and 423 respectively. The end points of line 420 represented at 427 and 428 represent the center of information trac~s 422 and 424, respectively. The end of line 421 at 429 represents the center of information track 423.
The waveform shown in line B of Figure 8 represents an idealized form of the frequency modulated signal output derived from the modulated light beam 4' during radial movement of the read beam 5 across the tracks 422, 424 and 423. This shows that a maximum frequency modulated signal is available at the area indicated generally at 430a, 430b and 430c which correspond to the centers 427, 42~ and 429 of the in-; for~ation tracks 422~ 4~4 and L'23, respec~ively. A
minlmum frequency modulated signal ls available at 431a and 431b wllich corresponds to the crossover points - 425 and 426. The wavefo.m shown on line ~ Or Figure 3 '1 _51- 1 i ~ 8 3 5 is genera~ed by radlally movln~ a focused lens across the surface Or a video disc 5.
Referring to line C of Figure 8, there is shown the difrerential tracklng error signal generated in the difrerential ampllfier 414 shown ln Flgure 7.
The difrerential tracking error signal ls the same as that shown in lil~e A of Figure 6C e~cept for the details shown in the Fi5ure 6C for purposes of explanation of the focus servo subs~Jstem peculiar to that mode of operation.
Referring again to Figure C of line 8, the differential tracking error signal output shows a first maximum tracl{ing error at a point indicated at 432a and 432b which is intermediate the center 428 of an informatic:l traclc 424 and the crossover point indi-cated at 425 or 425 depending on the direction of beam travel frcm ~he central trac}c 424. A second maximum trac~ing error is also shown at 434a and 434b corres-ponding to a track location interm~dlate the crossover points 425 and 425 between the inlormation track 424 and the next adjacent tracks 422 and 423. Minimum focus error is sho~n in line C at 440a, 440b and 440c corresponding to the center of the information tracks 422, 424 and 423, respectivel~T. Minimum tracking error signals are also shown at 441a and 441b corresponding to the crossover points 425 and 426, respectlvely. This corresponds with the detailed description given with reference to Figure 6C as to the importance cf identi-fylng which of the minimum differentlal tracking error signal outputs corresponds with the center of track location so as to insure proper focusing on the center of an information track and to avoid attemptlng to focus upon the track crossovers.
Referring to line D of Figure 8, there ls shown the differential focus error signal output wave-form generated by tlle differential amplifier 408. The waveform is indicated generally by a line 442 which moves in quadrature with the differenti~l tracking error signal s;lown with reference ~o line C of Flgure 8.

.

.

5.~ 1150835 Relerring to Fi~ure 9 there ls sho~1n a scllematlc bloclc dia6ram of the tracking servo subsystem 40 emplo~ed in the video disc pla~er 1. The dlfferen-tial trackln~ error is applied to a trackin~ servo loop interrupt s~itch 4So over the llne 40 from the signal recovery system 30. The loop interrupt signal is ap-plled to a ~ate 482 over a llne 108 from the stop motion subsystem 44. An open fast loop command signal ls applied to an open loop fast gate 484 over a line 180~ from the function generator 47. As previously me~tioned the functlon generator includes ~oth a re-mote control unit from which commands are received and a set of console switches from which commands can be received. Accordingly the command signal on line 180b is diagra~matically shown as the same signal applled to the carriage servo fast forward current generator over a line 180b. The console s~itch is sno~n entering an open loop fast gate 48~ over the line 180b'. The fast reverse command from the remote con-trol pcrtion o~ the function generator 47 is appliedto the open loop ~ast gate 484 over the line 180b.
The fast reverse command from the console portlon of the function generator 47 is applied to the open loop fast gate 486 over the line 180b'. The output from the gate 484 is applied to an or gate 488 over a llne 490.
The output from the open loop fast gate 486 ls applied to the or gate 488 over a llne 492. The flrst output from the or gate 488 is applied to the audio processing system 114 to provide an audio squelch output signal on 3 the line 116. A second output from the or gate 488 is applied to the gate 482 as a gating signal. The output from the tracking servo open loop switch 480 is applied to a junction 496 connected to one side ~ a resistor 498 and as an input to a trackin~ mirror amplifier driver 500 over a line 505 and an ampllfier and fre-~uenc~ compensation net--ork 510. The other end o~ the resistor 498 is connected to one slde of a capacitor 502. The otl~er side of the capacitor 502 ls connected to ground. The amplifier 5C0 receives a second input -53- ~835 si~nal from the stop motion subsystem 44 over the llne lOo. The si~nal on the line 106 is a stop mDtion com-pensation pulse.
The function of the amplifier 510 is to provide a DC component of the traclcln~ err~r, developed over the comblnation of the resistor 498 and capacltor 502, to the carrlage servo system 55 during normal tracking perlods over a line 130. The DC component from the junction 496 is gated to the carriage servo 55 by the play enabling signal from the function generator 47.
The push/pull amplifier circuit 500 generates a first trac~lng A signal for the radial tracking mirror 28 over the line 110 and generates a second tracking ~ output signal to the radial tracking mirror 28 over the line 112. The radial mlrror requires a maximum of 600 volts across the mirror for maximum operating efficiency when bimorph type mirrors are used. Accordingly, the push/
pull amplifier circuit 500 comprises a pair of ampli-fier circuits, each one providlng a three hundred voltage swin~ for driving the tracking mirror 28.
To~ether, they represent a maximum of six hundred volts peak to peak signal for application over the lines 110 and 112 for controlling the operation of the radial track~ng mirror 28. For a better understanding of the tracking servo 40, the description of lts detailed mode ~ operation is combined with the detailed descrip-tion of the operation of the stop motion subsystem 44 shown with reference to Figure 12 and the waveforms shown in Figures 13A, 13~ and 13C.
TRACKING SERVO SU~SYSTEM - NORMAL MODE OF OPERATION
The video disc member 5 being played on the video disc player 1 contains approximately eleven thousand information tracks per inch The distance from the center Or one information track to the next ad~acent information track ls in the range ~ 1.6 microns. The information indicia ali~ned in an informa-tion track is approximately 0.5 microns in width. This leaves approximately one micron of empt~y and open space bet~een the outermost regions of the ~ndicia posltioned ~n adjacent lr.formation bearlng tracks.
The function of the trackin6 servo ls to direct the impingement of a focused spot of llght to imp ct directl~J upon the center of an informatlon track.
The focused spot of light ls approximately the same wldth as the ~nformation bearing sequence of indicia which form an information track. Obviousl~J, maximum signal recovery is achieved when the focused beam of light is caused to travel such that all or most of the light spot impinges upon the successively positioned light reflective and light non-reflective regions of the information track.
The tracking servo is further identified as the radial tracking servo because the departures from 15 the information track occur in the radial dlrection upon the disc surface. The radial tracking servo is continuously operable in the normal play mode.
The radial tracking servo system is interrupted or released frcm the differential tracking error signal 20 generated from the FM video information signal recov-ered from ttle video dlsc 5 in certaln modes of opera-tion. In a first mode ~ operation, when the carrlage servo lC causing the focused read beam to radially traverse the information bearing portion of the video 25 disc 5, the radlal tracklng servo system 40 is released from the effects of the differential tracking error signal because the radial movement of the reading beam is so rapid that tracklng is not thought to be neces-sary. In a ~ump back mode of operation wherein the 30 focused reading beam 4 ls caused to ~ump from one track to an ad~acent track, the differential tracking error is removed from the radlal tracking servo loop for eliminating a signal from the tracking mirror drivers which tend to unsettle the radial mirror and tend to 35 requlre a longer period of time prior for tlle radial tracl{ing servo subs~ste~ to reac~uire proper trackin~
of the next adjacent information track. In this embod-iment of operatlon where the differential tracking error ls removed from the track~ng mirror drivers, a substitute .

llS0835 `

pulse is gel~erated for glving a clean unamblguous slgnal to th~ tracking m~rror drivers to direct the tracking mirror to move to its next assigned location. This siGnal in the preferred embodiment is identiried as the stop motion pulse and comprises regions of pre-emphasis at the beginning and end of the stop motion pulse which are tailored to direct the tracking mirror drivers to move the focused spot to the predetermined next traclc location and to help maintain the focused spot in the proper tracking position. In review, one mode ~ operation of the video disc player removes the differential tracking error signal from application to the tracking mirror drivers and no addition~l signal is substituted therefor. In a further embodiment of operation of the video disc player, the differential tracking error signal ls replaced b~J a particularly shaped stop motion pulse.
In a still further mode of opera'ion of the tracking mir,or servo subsystem 40, the stop motion pulse which is employed for dlrecting the focused beam to leave a f,irst information traclc and depart for a second adjacent information track is used in combina-tion with a compensation signal applied directly to the radial tracking mirrors to direct the mirrors to main-tain focus on the next adjacent track. In the preferr~embodiment, the compensation pulse is applied to the tracking mirror drivers after the terminatlon Or the stop motion pulse.
In a still further embodiment of the tracking servo subsystem 40$ the differential tracking error signal is interrupted for a period less than the time necessary to perform the stop motion mode of operation and the port1on of the differential tracking error allowed to pass into the tracking mirror drivers is calculated to assist the radial traclcing mirrors to achie~e proper radial tracking.
Referring to Figure 11, there is shown a block diagram of the tangential servo subsystem 80. A flrst input signal to the tangential servo subsystem 80 is ;

.

-~ 6~ 083S
appl~ed from the FM processlng system 32 over the line ~2. The signal present on the line 82 is the video signal available frcm the vodeo distribu'ion ampli-fiers as contained in the FM processing system 32. The video sigllal on the line 82 ls applied to a sync pulse separ2tor circuit 520 over a line 522 and to a chroma separator fil~er 523 over a line 524. me video signal on the line 82 is also applied to a burst gate separa-tor circuit 525 over a line 525a.
The function of the vertical sync pulse separ-ator circuit 520 is to separate the vertical sync signal from the video signal. The vertical sync signal is applied to the stop motion subsystem 44 over the line 92. The function Or the chroma separator filter 523 's to separate the chroma portion fro~ the total video si~nal received from t~le FM processing circuit 32.
The output from the chroma separator filter 523 ls ap-plied to the FM corrector portion of the FM process-~ ing circuit 32 over the line 142. The output signal from the chroma separator filter 523 is also appliedto a burst phase detector circuit 526 over a llne 528.
The burst phase detector circuit 526 has a second input signal from a color subcarrier oscillator circuit 530 over a line 532. The p~rpose of the burst phase de-tector circuit 526 is to compare the instantaneousphase of the color burst signal with a very accurately generated color subcarrier oscillator signal generated in the oscillator 530. The phase dlfference detected in the burst phase detector circuit 526 is applied to a sample and hold circuit 534 over a line 535. The f`unction of the sample and hold circuit is to store a voltage equivalent of the phase difference detected in the burst phase detector circult 526 for the tlme during which the f`ull line of video information containing that color burst signal, used in generating the phase difference, is read from the disc 5.
The purpose of the burst gate separator 525 ls to generate an enabling signal indicating the tlme during which the color burst portion of the video .

.

~` 1150835 ( wa~erorm is received from the FM processlng unlt 32.
The output ~i~nal from the burst gate separator 525 is applied to the FM corrector portion of the FM
processing system 32 over a llne 144. The same burst 5 ~ate timin~ signal is applied to the sample and hold circuit ~4 over a line 538. The enabling signal on the line 53S gates the input from the burst phase de-tector 526 into tlle sample and hold circult 534 during the color burst portion of the video signal.
The color subcarrier oscillator circuit 530 applies the color subcarrler frequency to the audio processing circuit 114 over a line 140. The color subcarrier osclllator clrcuit 530 supplies the color subcarrier frequency to a dlvide circuit 540 over a 15 line 541 which divides the color subcarrier frequency by three hundred and ei~hty-four for generating the motor reference frequenc~. The motor reference fre-quency signal is applied to the spindle servo subsyst~m 50 over the llne 94.
The output from the sample and hold circuit 531' is applied to an automatic gain contrclled ampli-fier circult 542 over a line 544. The automatic gain controlled amplifier 542 has a second input signal from the carriage position potentiometer as applied thereto over the line 84. The function of the slgnal on the line 84 is to change the ~ain of the amplifier 542 as the readln~ beam 4 radially moves from the inslde track to the outside track and/or conversely ~hen the reading beam moves from the outslde track to the inside track.
The need for this adjustment to change with a change in the radlal position is caused by the formation of the reflective regions 10 and ..on-reflective reglons 11 with dif~erent dimensions from the outisde track to the inside track. The purpose of the constant rotational 3~ speed from the spindle motor 48 is to turn the disc 5 through nearly thirty revolutions per second to provide thirty frames of in~ormation tothe television recelver 96. The length of a track at the outermost clrcum-ference is much lon~er than the length of a track at -5~
tlle innermost circumference. Since the sa~e amount Or information is stored in one revolution at bcth the inner and outer circumference, the si~e Or the reflec-tive and non-reflective re~ions 10 and 11, respectively~
are adjusted from the inner radius to the outer radius.
Accordingly, this change in size requires ihat certain adjustmentsin the processing of the detected signal read from the video disc 5 are made for optimum opera-tion. One of the required adjustments is to adjust the gain of ~he amplifier 542 which ad~usts for the time base error as the reading point radi211y changes from an insiae to an outside circumference. The carriage position potentiometer (not shown) generates a suffi-ciently accurate reference voltage indicating the radial position of the point of impingement of the reading beam 4 onto the video disc 5. The output from the amplifier 542 is applied to a compensation circuit 545 over a line 546. The compensation netv:ork 545 is employed for preventing any system oscillations and instability. The output from the compensation net~ork 545 is applied to a tangenti~l mirror dr~ver circuit 500 over a line 550. The tangential mirror driver circuit 500 was described with reference to Figure 9.
The circuit 500 comprises a pair of push/pull ampli-fiers. The output from one of the push/pull amplifiers (not shown) is applied to the tangential mirror 26 t over a line 88. The output fromthe second push/pull ampllfier ~not sho-Jn) is applled to the tangential mirror 2~ over a line 90.
3 TIME PASE ERROR CORP~CTION r~ODE OF OPERATION
-The recovered FM video signal, from the surface of the video disc 5 is corrected, for ti~e base errors lntroduced ~y the mechanics of the reading process, in the tangential servo subsystem 80. Time base errors 3~ are introduced into the reading process due to the minor imperrections in the video disc 5. A time base error introduces a slight phase change lnto the re-covered F~l video signal. A typical time base error base correction system includes a highly accurate -1150835 ( oscillator for generating a source Or signals used as a phase standard for comparlson purposes. In the pre-rerred embodiment~ the accurate oscillator is conven-iently ch~sen to oscillate at the color subcarrier frequency. T:~e color subcarrier frequency ls also used during the writing process rOr controlling the speed of revolution Or the writing disc during the ~riting process. ~n this manner~ the reading process is phase controlled by the same highly accurate oscil-lator as ~as used in the writing process. The outputfrom the highly controlled oscillator is compared with the color burst signal of a Frq color video signal. An alternative system records a highly accurate frequency at an~J selected frequency during the writing process.
During the reading process, this frequency would be compared ~ith a highly accurate oscillator in the player and the phzse difference between the t~o signals is sensed and is employed for the same purpose.
The color burst signal forms a small portion Or the recovered FM video signal. A color burst signal ls repeated in each line of color T.V. video information in the recovered FM video signal. In the preferred embodiment, each portion Or the color burst signal is compared .~ith the hlghly accurate subcarrier oscillator signal for detecting the presence of any phase error.
In a different embodiment, the comparison may not occur during each availabllity of the color burst signal or lts equivalent, but may be sampled at randomly or pre-determined locations in the recovered signal containing the recorded equivalent of the color burst slgnal.
When the recorded information is not so highly sensi-tive to phase error, the comparison may occur at greater spaced locations. In general, the phase difference bet~Jeen the recorded signal and the locally generated s$gnal is repetitively sensed at spaced locations on the recordin~ surface for adjusting or p}lase errors in the recovered signal. In the preferred embodiment this repetitive sensing for phase error occurs on each line Or the FM video si6na.

'- 115083S
The detected phase error is stored ror a period o~ time extendin~ to the next sampllng process.
This phase error is used to ad~ust the readlng posi-ticn Or ~le reading beam so as to lmpin6e upon the video dlsc at a locatlon such as to correct for the phase error.
Repetitive comparison Or the recorded signal with the locally generated, highly accurate ~requency, continuousl~r ad~usts for an incremental portlon of the recovered video signal recovered during the sampling periods.
In the preferred embodiment, the phase error chan~es as the reading beam radially tracks across the information bearing surface portion of the video disc 5.
In this embodiment, a ~urther signal is required for adjusting the phase error according to the lnstan-taneous location of the reading beam to adjust the phase error according to its lnstantaneous location on the information bearing portion of the video disc 5.
This additional signal is caused by the change in physical size of the lndicia contalned on the video disc surrace as the radial tracking position changes ~rom the inner location to the outer location. The same amount of information is contained at an inner radius as at an outer radius and hence the indicia must be smaller at the inner radius when compared to the lnd~cla at the outer radius.
In an alternative embodiment, when the size Or the indicia ls the same at the inner radius and at the outer radius, this additional signal for ad~usting for instantaneous radial position is not required.
Such an embodiment would be operable with video disc members which are in strip ~orm rather than in disc form and when the inrormation ~s recorded using indicia of the same size on a video disc member.
In the preferred em~odi!De.~t, a tangential mlrror 26 ls the mechanlsm selected ~or correcting the tlme base errors introduced by the mechanics ~ the reading system. Such a mirror is electronically r controlled and is a means for changlng the phase ~ the recovered vldeo signal read ~`rom the disc by changing the time base on whlch the signals are read from the disc. Thls is achieved by directing the mlrror to read the lnformation from the disc at an lncremental point earlier or later ln tine when compared to the time and spacial location during which the phase error as detected. The amount of phase error determines the degree of chan~e ln locatlon and hence time in which 10 t;le informatlon is read.
~ hen no phase error is detected in the time base corr4cting system the point of impingement of the read beam with the video disc surface 5 is not moved.
'~Jhen a phase error is detected during the comparison 5 period, electronics signals are generated ror changing the point of impingement so that the recovered lnforma-tion from the video disc is available for processing at a point in time earlier or later when compared to , the comparison period. In t~.e pre~erred embodiment, this is achieved by changing the spacial location of the point of intersection of the read beam with the video dlsc surface 5.
Referring to Figure 12, there ls shown a block dlagram of the stop motlon subsystem 44 employed in 25 the vldeo disc player 1. The ~:aveform shown with reference to Figures 13A, 13B and 13C are used ln conJunction with the block diagram shown ln Figure to explain the operation of the stop motion system.
The video signal from the FM processing unit 32 is 3 applied to an input bufrer stage 551 over the line 134.
The output signal from the buffer 551 is applied to a DC restorer 552 over a llne 554. The functlon Or the DC restorer 552 is to set the blanklng voltage level at a constant unlform level. Varlatlons in signal 35 recording and recover~J oftentlmes result ln video signals available on the line 134 with difrerent blank-ing levels. The output from the DC restorer 552 is applied to a white rlag detector circuit 550 over a line 558. The function of the wilite flag detector 55S

a2 1~0835 is to idelltif~ the presence Or an all w~llte 'evel vldeo signal existing during an entire line of one or both fields cont~ined in a frame of television informstion.
I~'hile the white flag detector has been described as being detecting an all white video signal during a complete line interval of a frame of television in-formation, the white flag may take otller forms. Cne such form would be a special number stored in a line.
Alter~atively, the white flag detector can respond to the address indicia round in each video fr~me for the same purpose. Other indicia can also be employed. How-ever, the use of an all white level slgnal during an entire line interval in the television frame of in-formation has been found to be the most reliable.
The vertical sync signal from the tangential servo ~0 is applied to a delay circuit 560 over a line 92. The output from the delay circuit 560 is supplied to a vertical -~indow generator 55~ over a line 5a4.
~ The function of the window generator 5S2 is to gener-ate an enabling signal for application tothe white fla~
detector 55~ ove, the line 55O to coincide with that line interval in which the whlte flag signal ha~ been stored. The output signal from tne generator 552 gates the predetermined ~rtion of the video slgnal 2~ from-the FM detector and generates an output white flag pulse whenever the white flag is contained in the portion of the video signal under surveillance. The output from the white flag detector 556 is applied to a stop motlon pulse generator 567 over a line 558, a gate 30 569 and a further line 570. The gate 569 has as a second input signal, over the line 132, the STOP MOTION
MODE enabling signal ~rom the function generator 47.
The differential tracking error from the signal recovery subsystem 30 is applied to a zero crossing 35 detector and delay circuit ~71 over the lines 42 and 45. The function Or the zero crossing detector circuit 571 is to identify when the lens crosses the mld-points 425 and/or 425 between two ad~acent tracks 424 and 423.

-~3- ~150835 It is important to note that the dlfrerentlal trackl~
sisnal output also indicates the same level slgnal at polnt 440c which identifies the optlmum focuslng point at which the tracking servo system 40 seeks to posltion the lens in perfect tracking allgnment on the mid-point 429 o~ the trac`.~ 423 w;len the tracklng suddenly ~umps from track 424 to track 423. Accordingl~, a means must be provided for recogni~ing the difference between points 441b and 440c on the differential error signal 10 shown in llne C of Figure 8.
The output of the zero crossing de~ector and delay circuit 571 is applied to the stop motion pulse generator 567 over a line 572. The stop motion pulse generated in the generator 567 is applled to a plurality Or locations ~l~e first Or ~hlch ls as a loop interrupt pulse to the tracking servo 40 over the line 108. A
second output sigr.al ~rom the stop motion pulse gener-ator 5~7 is applied to a stop motion compensation se-quence generator 573 over a line 574a. The function of the stop motion compensatlon sequence generator ~73 ~ is to generate a compensation pulse waveform for appli-cation to the radial tracklng mirror to cooperate with the actual stop motlon pulse sent directly to the track-ing mirror over the line 104. The stop motion compen-sation pulse ls sent to the tracking servo over the line 10~.
With reference to line A of Figure 8, the center to center dlstance, indicated by the line 420, between adjacent tracks is presently fixed at 1.6 microns. The tracklng servo mlrror galns sufficient lnertia upon receiving a stop motion pulse that the focused spot from the mirror ~umps from one track to the next ad~acent track. The inertla Or the tracking mirror under normal operatlon conditions causes the mirror to swing past the one track to be ~umped.
Priefl-vT, tlle stop motion ~UiS2 011 tlle line 104 causes t~le radial trackin~ mirror 2~ to leave the track on whlch it is tracking and ~ump to the next sequential track. A short time later, the radial tracking mirror -54- 1~50835 recei~es a s~op motion compensation pulse to remove the added inertia and direct the tracklng mlrror into trackins the next ad~acent track wlthcut skipping one or more tr~cl~s before selectin~ a track for tracking.
In order to insure the optimum cooperation between the stop motion pulse from the generator 567 and the stop motion compensation pulse rrom the gener-ator 573, the loop interrupt pulse on line 108 is sent to the tracking servo to remove the differential tracl~irg error signal from being applied to the track-ing error amplifiers 500 during the period of time that the mirrcr is purposely caused to leave one track und~r d~rection of the stop motion pulse from the generator 557 and to settle upon a next adjacent track under the direction of the stop motion compensation pulse fr~m the generator 573.
As an introduction to the detail understand-ing of the interaction between the stop motion system ~ 44 and the tracking servo syste~ 40, the ~aveform shol~n in Fi~ures 13A, 13B and 13C are described.
Referring to line A of Figure 13A, there is shown the normal tracking mirror drive signals to the radial tracking mirror 28. As previously discussed, there are two driving signals applied to the tracking mirror 2~. The radial tracking A signal represented by a line 574 and a radial tracking B signal represented by a line 575. Since the information tracl~ is normally in the shape o~ a spiral, there is a continuous track-ing control signal being applied to the radial tracking mirror for follo~ing the spiral shaped configuratlon of the information track. The time frame o~ the in~ormat~on shown in the waveform shown in llne A
represents more than a complete revolution o~ the disc.
A typlcal normal tracking mirror drive signal waveform for a single revolution of the dlsc is represented by the lengt!l of the line in~icated at 57G. The two dis-continuities showil at 578 and 580 on waveforms 574 and 575, respectively3 indicate the portion Or the normal tracking period at which a stop motion pulse is given.

` `` ` 1150~}35 ~,~
The stop motion pulse ls also referred to as a ~ump back sigr.al and these two terms are used to descrlbe the outpui rom the generator 567. The sto~ motlor.
pulse is represented b~J the small vertically dlsposei dlscor.tinuit~T present in the lines ~74 and 575 at points 578 and 580, respectively. The rem2~ni~g wave-forms contained in Figures 13A, 13~ and 13C are on an expanded time base and represent those electrical slgnals which occùr Just before the beginning of this ~ump back perlod, through the ~ump back perlod and continuing a short duratlon beyond the jump back period.
The stop motion pulse generated by the stop motion pulse generator 5S7 and applied to the tracklng servo system 40 over the llne 104 is represented cr.
line C of Figure 13A. me stop motion pulse ls ldeally not a squarewave but has areas of pre-emphasis located generally at 582 and ~84. These areas of p.e-emphasis insure ~tlmum reliability ln the stop motion system 44. The stop motion pulse can be described as rising to a first higher voltage level during the initial period of the stop motion pulse period. Next, the stop motion pulse gradually falls off to a second voltage level, as at 583. The level at 583 is ma~n-tained during the duration o`f the stop motion pulse period. At the termlnatlon of the stop motlor puls~, the waveform falls to a negatlve voltage level at 585 below the zero voltage level at 586 and rises grad~ally to the zero voltage level at 586.
Llne D of Flgure 13 represents the d~f~eren-3 tlal tracklng error slgnal recelved from the recoverysystem 30 over the llnes 42 and 46. The waveform shown on llne D of Figure 13A ls a compensated dlffer-entlal trackin~ error achleved through the use of t~.e combination of a stop motlon pulse and a stop motion compensation pulse applled to the radial tracklng mirror 28 according to the teachir.g of the present inventlcn.
Line G of Figure 13A represents the loop inte~
rupt pulse generated by the stop motlon pulse generator ," 11~083~i ~o7 and applied to the tra~kill~ servo subs~stem 40 over the line 108. ~s previously mentioned, it is best to remove the dir~erential trackin~ error si~n~l as repre-sented b~r the t~ave~orm on line D rrom application to the radial trackin~ mirror 28 during the stop motion interval period. The loop interrupt pulse shown on line G achieves this gating function. However, by inspection, it can be seen that the dirrerential tracking error signal lasts for a period longer than tlle loop interrupt pulse shown on line G. The waveform shown on line E is the portion Or the dirferential tracking error signal shown on line D ~lhich survives the gating by the loop interrupt pulse shown on line G.
Ihe waveform shown on line E is the compensated track-ln~ error as in'errupted by the loop interrupt pulsewhich is applied to the tracking mirror 28. Referring to line F, the high frequency signal represented gener-ally under the bracket 590 indicates tne output waveform of the zero crossing detector circuit 571 in the stcp motion system 44. A zero crossing pulse is generated e ch time the dirferential error tracking signal shown in line D of Figure 13A crosses through 2 zero bias level. I~ile the information shown under the bracket 590 is helpl^ul in maintaining a radial tracking mirror 28 in tracking a single information track, such in-formation must be gated o~ at the beginning o~ the stop motion interval as indicated by the dashed lines 592 connecting the start o~ the stop motion pulse in line C of Figure 13A and the absence of zero crossing 3 detector pulses shown on line F of Figure 13A. ~y referring again to line D, the di~ferential tracking error signal rises to a ~rst maximum at 594 and falls to a second opposite but equal maximum at 596. At point 59~, the tracking mirror is passing over the zero crossing point 426 between tt~o ad~acent tracks 424 and 423 as shown with reTerence ~o line .~ OI` Flgure 8.
This means tllat the mirror has traveled half way ~rom the first track 424 to tlle second track 423. At thls point indicated by ~he number 598, ~lle zero crossinb .
. .

11~0835 detector generates an output pulse indicated at 600.
The output pulse 600 terminates the stop motion pulse shown on line C as represented by the vertical line segment 602. This termination of the stop motion pulse starts the negative pre-emphasis period 584 as pre-viously described. The loop interrupt pulse is not affected by the output 600 of the zero crossing de-tector 571. In the preferred embodiment, improved performance is achieved by presenting the differential tracking error signal from being applied to the radial tracking mirror 28 too early in the jump back sequence before the radial tracking mirror 28 has settled down and acquired firm radial tracking of the desired track.
As shown b reference to the waveform shown in line F, the zero crossing detector again begins to generate zero crossing pulses when the differential tracking error signal reappears as indicated at point 604.
Referring to line H of Figure 13A, thereis shown a waveform representing the stop motion compensation sequence which begins coincidental with the end of the loop interrupt pulse shown on line G.
Referring to Figure 13B, there is shown a plurality of waveforms explaining the relationship between the stop motion pulse as shown on line C of Figure 13A, and the stop motion compensation pulse waveform as shown on the line H of Figure 13A and re-peated for convenience on line E of Figure 13E. The compensation pulse waveform is used for generating a differential compensated tracking error as shown with reference to line D of Figure 13E.
Line A of Figure 13B shows the differential uncompensated tracking error signal as developed in the signal recovery subsystem 30. The waveform shown om Figure A represents the radial tracking error signal as the read beam makes an abrupt departure from an information track on which it was tracking and moves towards one of the adjacent tracks positioned on either side of the track being read. The normal tracking error signal, as the beam oscillates slightly down the , 5~ ~50835 lnrormatioll track, is shot~n at the region 510 of Line A
The trackin~ error represents the slight side to side (rqdial) motion of the read beam 4 to the successively positior.ed reI`lec~ive and non-reflective regions on the disc 5 as previously described. A point 612 represents ~he start o~ a stop motion pulse. The uncompensated tracking error is increasing to a first maximum indi-cated at 514. The region between 612 and 614 S}lOWS an increase in trackin~ error indicating the departure o~ the read beam from the track being read. From point 61~, the difrerential tracking error-signal drops to a pcint indicated at 616 which represents the mid-point o~ an information track as shown at point ~26 in line A
o~ Figure 8. However, the distance traveled by the read beam bet~een points 512 and 616 on curve A in Figure 13~ is a movement of o.8 microns and is equal to lengtll of line 617. The uncompensated radial track-ing error rises to a second maximum at point 618 as the read beam begins to approach the neY~t ad~acent track 423. The tracking error reaches zero at point 622 but is unable to stop and continues to a new maximum at 524. The radial trackin~ mirror 28 possesses suffi-cient inertia so that it is not able to instantaneously stop in -esponse to the differential tracking error signal detecting a zero error at point o22 as the read beam crosses the next adjacent information track.
Accordingly~ the raw tracking error increases to a point indicated at 524 wherein the closed loop servo-ing erfect of the tracking servo subsystem slows the mirror down and brings the read beam back towards the in~ormation track represented by the zero crossing dif-ferential tracking error as indica~ed at point 625.
Addltional peaks are ldenti~ied at 626 and 628. These shol~1 a gradual damping o~ the dlf~erential tracking error as the radial tracking mirror becomes graduall~J
positicned in its proper location to gener~te a zero tracking errorJ such as at points 612, 622, 625. Addi-tional zero crossing locations are indicated at 630 and 632. The portion of the wave~o~m shown in line A
i 11so~3s e~isting arter point 632 shows a gradual return Or the raw trac~in~ error to lts zero positlon as the read spot gradually comes to rest on the next adjacent track 423.
Point 615 represents a false indication o~
~ero tracking error as the read beam passes over the center 420 of t~e region between adJacent tracks 42"
anà 423.
For optimum operation in a stop motion situa-tior. wnerein the read beam Jumps to the next adjacent track, the time allowed ror the radial tracking mirror 28 to reacquire proper radial tracking is 300 micro-seccnds. This is indicated by t~le length of the line 634 sholJn on line ~. Py observation, it can be seen that the rad~al tracking mirror 28 has not yet reac-quired zero radial error position at the expiration of the 300 microsecond time period. Obviously, if more time ~ere available to achieve this res~lt, the wave-rorm shown ;wlth reference to Figure A would be suitable for those systerls having more time for the radial tracking mirror to reacquire zero differential trackin~
error on the center of the next adjacent tracls.
Ref`erring briefly to line D of Figure 13, line 634 is redrawn to indicate that the compensated radial tracking error signal shown in llne D does not include those large peaks shown with ref`erence to line A. The compensated di~ferential tracking error shown in line D is capable of achieving proper radial tracking by the tracl~ing servo subsystem within the 3 time f'rame allo~ed ror proper operation Or the video disc player 1. Referring briefly to line E of Figure 13A, the re~aining trac~ing error signal available after interruptioll b~y the loop interrupt pulse is of the proper direction to cooper2te ~ith the stop motion compensation pulses described hereinarter to bring the radial 'rac,._n~ mlrror ~o its op~ um r~ial ~racking position as soon as possible.
The stop motion compensatlon generator 573 shown wlth reference to Figure 12, applles the waveform ~o ~15083S
sho~n in line E o~ Figure 13E to the radial trackin~
mirror 2~ by way Or tlle line 105 and the amplifler 500 shown in Figure 9. The stop motion pulse directs the radial tr~cki!lg mirror 28 to leave the tracking of one inrormation track and begin to seek the tr~cking of the next ad~acent track, In response to the pulse ~rom the zero crossing detector 571 shown in Figure 12, the stop r.~otion pulse generator 557 is caused to generate the stop motion compensation pulse s'nown in line E.
lC Re~erring to line E of Figure 13~, the stop mo~ion compensation pulse waveform comprises a plural-it~J of lndividual and separate regions indicated at 540, 542 and 544, respectively. The ~ t region 640 of the stop motion compensation pulse begins as the dir~erential uncompensated radial tracking error at point 515 cross the zero reference level lndicating that the mirror is in a mid-track cross~ng situation.
At this time, the stop motior, pulse generator 557 generates the first portion 540 o~ the compensation pulse which is applied directl~; to the tracking mirror 28. The generation o~ tl~e first portion 640 of the stop motion compensation pulse has the effect of re-ducing th~ peak 624 to a lower radial tracking displace-ment as represented by the new peak 524' as shown in line ~. It should be kept in mind that the waveforms shown in Figure 13P are schematic only to show the overall interrelationship of the various pulses used ln the tracking servo subsystem and the stop motion subsystem to cause a read beam to ~ump rrom one track 30 to the next adjacent track. Since the peak error 624' ls not as high as tlle error at peak 624, this has the ef~ect o~ reducii~ the error at peak error polnt 526' and generally shifting the remaining portion of the ~aveform to the left such that the ~ero crossings at 35 o2~', 630' and 532' all occur sooner than they would have occurred ~Jitllout the presence of the stop motion compensation pulse.
Re~erring bac~ to llne E of Fi~ure 13~, the second portion 542 of the stop motion compensation -7i- ~ 3 5 ~ulse is of a second polarity when compared to the first region S40. The second portion 542 of vhe stop motlon compensation pulse occurs at a point in tlme to compensate for the tracklng error shot~n at 626' of line ~. This results in ar. even smaller radial track-lng error being generated at that tlme and this smaller radial tracking error ls represen~ed as point ~26" on line C. Since the degree of the radial tracking error represented by the point 626" of line C is significantlj smaller than that sho~rJn with reference to point 526' Or iine ~, the maximum error in the opposite direction shown at poir.t 625' ls again significantly smaller than that represented at point ~25 of line A. This counteracting of the natural tendency of the radial trackin~ mirror 28 to oscillate back and forth over the inform~tion track is furtller dampened as indicated by the furth2r movement to the left of points 628" and 525 with reference to their relative locations show in lir.es ~ and A.
Re~erring again to line E of Figvre 13~ and the third region ~44 of the stop motion compensation pulse, this region 544 occurs at the time calculated to dampen the remaining long term traclcing error as represented that portion o~ the error signzl to the right of the zero crossing point 532" shown in line C.
Region 644 is shown to be approximately equal and opposite to thls error signal which would exist if the portion 644 of compensation pulse did not exlst. Re-ferring to line D of Figure 13~, there is shol~n the differential and compensated radlal tracking error representative of the motion of the light beam as it is caused to depart from one information 'rack being read to the next adjacent track under the control of a stop motion pulse and a stop motion compensation pulse. It should be noted that the waveform shown in line-D of Figure 13~ can represent the movement in either directlon although the polarity Or various signals would be changed to represent the difrerent direction of movement.

~ he cooperation ~etween the st~p motion sub-system 44 and the tracking servo subsystem 40 duriil~ a stop motion period will now be described ~:ith reference to Flgures 9 and 12 and their related waveforms. Re-ferring to Figure gA, the tracking servo su~s~Jstem 40is in operat~on ~ust prior to the initiaticn of a stop mction mode to maintain the radial tracking mirror 28 in its position centered directly atop of information track. In order tc maintain this position, the differ-10 ential traclci:lg error is detected in the s~gnal recoverJsubsyste~ 30 and applied to the tracking s~rvo subsystem 40 by the line 42. In this present operating mode, the differential tracking error passes di-ectly through the tracl;i~g servo loop switch 480, the am?lifier 510 15 and the push/pull amplifiers 500. That pc-tion of the wav2form showr. at 591 on line D of Figure 13A as being traversed.
The function generator 47 gener2tes a stop motlon mode signal for application to the stop motion mode gate 559 over a lir.e 132. The ~unct on of the stop mOtiOIl mode gate 569 is to ~enerate a pulse in response to the proper location in a television frame for the stop motion mode to occur. This pclnt is de-tected by the combined operation of the total video signal from the FM processing board 32 bei n.g applied to the white flag detector 55S over a line 134 in com-blnation t~ith the vertical sync pulse developed in the tangential servo system 80 and applied ~er a line ~.
The windo~: gener~tcr 562 provides an-enabling signal which corresponds with a predetermined pc~tion of the video signal containlng the white flag indic2tor. The white flag pulse applied to the stop motlc~ mode gate 569 is gated to the stop motion pulse generator 567 in response to the enablillg signal received .rom the function generatcr 47 over the line 132. The enabling si~nal ~rom the stop motion mode gate 569 lnltiates the stop motion pulse as shown t~ith referen.ce to line C
of Figure 13A. The output from the zero crossing de-tector 571 indicates the end of the stop ~otion pulse 73 ~1~0835 period by applica'ion Or a si~nal to the stop motio~
pulse generator ~57 over the line 57~. The stop ~otion pulse from the ~enerator 567 is applied to the tracking servo loop interrupt switcll 430 b~- way of the gate 482 and the line ~8. The function of the track-lng servo loop interrupt switch ~80 is to remove t'ne dlfferential trackin~ error currently bein~ generated in the signal recovery subsystem 30 ~rom the pusy/pull am?lifiers 500 driving the radial tracking mirror 20.
10 Accordingly, the switch 480 opens and the differential tracking error is no longer applied to the amplifiers 500 for drlving the radial tracking mirror 28. Simul-taneously, the stop motion pulse fro~ the generator 567 is applied to the amplifiers 500 over tlle line 104.
15 The stop motion pulse, in essence, ls substituted for the differenti21 tracking error and provides a driving sigral to tl-le push/pull ampli~iers ~00 for starting the read spot to move to the next adjacent information track to be read.
The stop motlon pulse from the ~enerator 567 is also applied to the stop motion compensatlon sequence generator 573 wherein the waveform shown with reference to line H of Figure 13A and line E of Figure BR is generated. Py inspection of line H, it is to be noted that the compensation pulse shown on line H occurs at the termination of the loop interrupt pulse on line G, which loop interrupt pulse is triggered by the start of the stop motion pulse shown on line C. me compensa-tlon pulse is ~pplled to the push/pull amplifiers 500, 3 over the line 10~ shown in Figures 9 and 12, for damp-ing out any oscillation in the operation of radial tracking mirror 28 caused by the applicatLon of the stop motion pulse.
As previously mentioned, the compensation pulse is initiated at the termination of the loop interrupt signal. Occurring simult~neousl~r with the generation of the compensatlon pulse, the tracking servo loop interr~lpt switch 480 closes and allows the differential trackir.g error to be reapplied to the ,_ _ , .

push/pull ampli~iers 500. The typical waverorm aval~-able at t~is poii-i~ is sho~ ln line E Or ~igure 13A
t~hich cooperates ~Jith the stop motion com~ensatlon pulse to ~uickly bring the radial tracking mirror 28 into suitable radial tracking ali~nment.
Referrii~ brlefly to llne A Or Figure 13C, t~o frames o~ televisicn vldeo information being read from the video disc 5 are sho~m. Line A represents the differential tracking errcr signal having a~rupt dis-continuities located at 550 and 652 representing thestop motion mode of operation. Discontlnuities of smaller amplitude are shown at S54 and 656 to show the ef~ect of errors on the surface of tlle video disc surface in the diLferential tracking error signal.
Line ~ Or Figure 13C shows the FM envelo~e as it is read rrom the video disc surface. The stop motion periods at 6~3 and 650 sllow that the Fr~ envelope is temporarily interlupted as the reading spot jumps tracks. Changes in the FM envelope at 662 and 664 show the te~pcrary loss of Fi~ as tracking errors cause the tracking beam to temporarily leave the informatlon track.
In review Or the stop motion mode of opera-tion, the following combinatio~s occur in the preferred embodiment, In a first embodiment, the differential tracking error signal is removed from the tracking mirror 28 and a stop motion pulse is substituted therefol to cause the radial tracking mirror to ~ump one track fromthat track being tracked. In this 3 embodiment, the stop motion pulse has areas of pre-emphasis such as to help the radial traclcing mirror to re~ain tracking of the ne~ track to which it has been positioned. The differential trackin~ error is re-applied into the tracking servo subsystem and cooperate with the ~top motion pu15-' applied to the radial trac!:-lr.g mirror to reacquir~ radial track~ . The dirferen-tial tracking error can be re-entered into the trackinæ
servo system for optlmum results. In this embodiment, the duration of the loop interrupt pulse is varied for .

1~50835`

gavlng cr~ the application of tl~e differential track-ing error into the push/pull amplifiers 500. The stop motion pulse is of fixed length in this embodiment.
Al alternative to this fixed lengtll Or the stop motion pulse ~s to initiate the end o~ the stop motion pulse at the first zero crossing detected a~ter the ~eginning of the stop motion pulse was initiated. Suitable del~ys can be entered lnto this loop to remove an~J
extraneous signals that may slip through due to mis-alignment of the beginnil~ of the stop motion pulseand the detection of zero crossings in the detector 571.
A further embodiment lncludes any one of the above combinations and further includes the generation of a stop motion aompensation sequence. In the pre-ferred embodi~ent, the stop motion compensation se-quence is initiated with the termination of the loop interrupt period. Coincidental with the termination Or the loop interrupt period, the differential track-20~ ing error is reapplied into the tracking servo sub-- system 40. In a further embodiment, the stop motion compensation pulse can be entered into the trac~lng servo subsystem over the line 106 at a ~eriod fixed in time from the beginning o~ the stop motion pulse as 2~ opposed to the ending of the loop interrupt pulse. The stop motlon compensation sequence comprises a plurality of separate and distinct regions. In the preferred embodiment, the first region opposes the tendency of the tracking mirror to overshoot the next adjacent track and directs the mirror bacl; into radial tracklng of that next ad~acent parvicular track. A second region is Or lower amplltude than the first region and of opposl~e polarity to further compensate the motion of the radial tracking mirror as the spo' again over-3~ shoots the center portion of the next ad~acent trackbut in the opposlte direction. ~l~e third region of t~le stop motion compensation se~uence is of ~he same polarity as the rirst region, but of signiricantly lol~er amplltude to further compensate an~J tendency o~

-75- ~.150835 tlle radial trackin6 mirror having the focus spot agaln leave the inrormatlon track.
lhile in the preferred embodiment, the various regions Or the stop motion sequence are shown to consist 5 of separate individual regions. It is possible for these re~ions to be themselves broken down into in-dividual pulses. It has been found by experimeni that the various regions can provide enhanced operation ~hen separated by ~ero level signals. More specific-ally, a zero level condition exists between regionone and region two allowing the radial tracking mirror to ~ove under its own inertia without the constant applicatiDn of a porticn of the compensation pulse.
It has also been found by experiment that this quiescent period of the compensation sequence can coincide with the reaDplication of the differential tr~cking error to the radial tracking mirrors. In this sense, region one, showll at 640, of the compensation sequence cooper-ates with the pcrtion 604 sho~n in line E of Figure 13A
from the dirferential trackln~ error input into t~le tracking loop.
~ y observation Or the compensation waveform shGwn in line E of Figure 13~, -lt can be observed that the various regions ter.d to begin at a high amplitude and fall off to very low compensation signals. It can also be observed that the period Or the varlous regions begin at a first relatively short time period and gradually become longer in duration. Thls coin-cides with the energy contained in the ~rackin~ mirror as lt seeks to regain radial tracking. Initially in the track ~umping sequence, tl~e energy is high and the early portions of the compensation pulse are appro-priately hi~h to counteract this energy. There~fter, as energy is removed ~rom the tracking mirror, the ~5 corrections become less so as to bring the radial tracking mirror back into radial alignment as soon as possible.
Refer1ing to FlOure 14, there is shown a block diagram of ~he ~M processing system 32 employed in the video disc pl~yer 1. The frequency modulated video si~nal recovered from the disc 5 forms the input to the F~l processing unit 32 over the line 34. The frequency ~odulated vldeo s~gnal is applied to a dis-tribution amplifier 670~ The distributicn amplifierprovides three equal unloaded representations ~f the received signal. The first output signal from t~.e distribution amplifier is applied to a FM corrector circuit 572 over a line 673. The F~ corrector circuit 572 operates to provide variable gain amplification to the received freauency mcdulated video signal to compensate for the mean trans-er function of the lens 17 as it reads t~he frequency modulated video signal from the disc. The lens 17 is operating close to its absolute resolving pol~1er and as a result, recovers the frequency modulated video signal with different ampli-tudes correspGnding to different frequencles.
The output fror" the FM corrector 672 is applied to 2n Fl~ detector 574 over a line 575. The FM detec'or gellerates discrimi:lated video for applica-ti~.. to the remainlng circui~s requiring such dis-crimirated video in the video disc player. A second output signal from the distribution amplifier 670 is applied to the tangential servo subs~Jstem 80 over a line 82. A further output signal from the distribu-tion amplifier 670 is applied to the stop motion sub-system 44 over the line 134.
Referring to Figure 15, there is shown a more detailed block dlagram of the FM corrector 672 sho~m in 3 Figure 14. The FM video signal from the amplifier 570 is applied to an audio subcarrier trap circuit 576 over the line 673. The functioll of the subcarrier trap circuit 675 is to remove all audio components from the frequency modulated video signal pricr to application to a frequenc-y selective variable gain ampli ier 678 ove~ q li~e 58~.
The control signals for operatin6 the amplifler 678 include a first burst gate detector 582 havlng a plurali~y of input signals. A first input signal is the _ " 11508;~

chrcma portion o~ the FM video si~nal as applied over a line 142. The second input signal to the burst gate 682 is ille burst gate enable signal from the tangertial servo system 80 over the line 144. The function of the burst gate 582 is to gate into an amplitude detector 68~ over a line 685 that portion Or the ch,oma signal corresponding to the color burst signal. The output from the amplitude detector 684 i s applied to a summa-tion circuit 588 over a line 690. A second input to 10 the sumrnation circuit 588 is from a variable burst level adjust potentiometer ~92 over a llne 594. The function Or the amplitude detector 584 is to determine the rirst order loller chroma side band vector and apply it as a current representation to the summation circuit 688. The burst le~el adjust si~nal on the line 694 rrom the potentiometer 692 operates in con~unction ~ith this vector to develop a control signal to an amplifier 696. The output from the summation circuit is applied to the amnlifier 595 over the line 698. The output from the ampli~ier 695 is a control voltage for applica-tio" to the amplirier 678 over a line 7~0.
Rererrin~ to Figu-e 15, there is shown a numDer Or wave~orms he 1PT~U1 in understanding the operation of the FM corrector sho~n in Figure 15. The waveform repre-sented by the line 701 represents the FM correctortransfer function in generating control voltages for application to t'ne amplifier 678 over the llne 700.
- m e line 702 includes four 6ections of the curve indi-cated generall~ at 702, 7~4, 705 and 708. These segments 702~ 704, 705 and 708 represent the various control voltages generated in response to the con!-parison with the instantaneous color burst signal amplitude and the pre-set level.
Line 710 represents the mean transrer functlon Or the objective lens 17 emplo;~ed for reading the successive li~ht reflective re~ions ~ ar.d li~ht nor.-rerlectlve re~ions 11. It c~n be seen upon lnspection that the ~ain versus frequenc~J response of the lens falls Orr as the lens reads the rrequency modulated 115()835 represelltati3ns Or the video signal. ~eferrin~ to the remair.lng portion of Figure 16, there is shotln the frequenc~ spectrum of the frequency modul ted signals as read rrom the video disc. This indicates that the video si~nals are located principally between the 7.5 and 9.2 megahertz region ~t which the frequenc~J re-sponse of the lens shown on line 710 is showing a sig-nificant decrease. Accordingly, the control ~oltage from the amplifier 696 is variable in nature to com-pensate ror the frequency response of the lens. Inthis manner the effective frequency response o~ the lens is brought into a normalized or uni~orm region.
F~l CORRECTOR SU~SYSTEM - NORr~L MODE OF OPERATIOM
.
The FM corrector subsystem functions to adjust the FM video signal recelved from the disc such that all recovered FM signals over the entire frequency spectra of the recovered FM signals are all amplified to a level, relative one to the other to reacquire their substantially identical relationships one to the other as they existea during the recording process.
The microscopic lens 17 employed in the video disc player 1 has a mean transfer characteristic such that it attenuates the higher frequencies more than it attenuates the lo~Jer frequencies. In this sense, the lens 17 acts similar to a low pass filter. The function of the FM corrector is to process the received FM
video si~nal such that the ratio of the luminance sig-nal to the chrominance slgnal is maintained regardless o~ the position on the disc from which the FM video signal ls recovered. This is achieved ~y measuring the color ourst signal in the lower chroma side band and storing a representation o~ its amplitude. This lo~.~er chroma side band signal functions as a reference ampli-tude.
The FM video signal is recovered from the video disc as previously described. The chrominance signal is removed rrom the FM video signal and the burst gate enable signal gates the color burs~ signal present on eac'n line of F~ video in~ormation into a 115(~83~
-~o -compariscn operation. The comparison operation effec-tively operates ~or sensinæ the dif~erence between tlle actual amplitude of the color burst signal re-covered from the video disc sur.ace with a reference amplitude~ The reference amplitude has been ad~usted to the correct level and the comparison process indi-cates an errcr signal between the recovered amplitude of the color burst signal and the reference color burst signal indicating the difference in ampl~tude between the two signals. The error signal generated in this comparison operation can be identified as the color burst error amplitude signal. This color burst error amplitude signal is employed for ad~usting the gain of a variable gain amplifier to amplify the signal presently being recovered from the video disc 5 to amplify the chrominance signal more than the luminance signal. This variable amplification provides a var-iable gain over the frequency spectrum. mhe higher frequencles are amplified more than the loi~er fre-quencies. Since the chrominance signals are at thehigher frequencies, they are amplified more than the luminance signals. This variable amplification of signals results in effectively maintaining the correct ratio of the luminance signal to the chrominance signal as the reading process radially moves from the outer periphery to the inner periphery. As previously men-tioned, the lndicia representing the FM video signal on the video disc 5 change in size from the outer perlphery to the inner periphery. At the inner periphery they 3 are smaller than at the outer periphery. The smallest size indicla are at the absolute resolution power of the lens and the lens recovers the FM signal represented by this smallest size indlcia at a lower amplitude value than the lower ~requency members which are larger in size and spaced farther apart.
In a preferred mode of operation, the audio signals contained in the F.~ video signal are removed from the FM video signal before application to the variable gain amplifier. The aud~o in~ormation ls . .

contained around a number of FM subcarrier slgnal~
and it has been found by experience that the removal of these F~ subcarrier audio signals provides enhanced correction of ~he remainlng video FM signal in the var-iable gain amplifier.
In an alternatlYe mode of operation thefrequency band width applied to the variable gain amplifier is that band width which is affected by the mean transfer function of the ob~ective lens 17. More specifically, when a portion of the total FM recovered ~rom the video disc lies in a range not affected by the ~ean transfer function, then this portion of the total waveform can be removed from that portion of the F~l signal appl~ed to the varlable gain amplifler. In this manner, the operation of the variable gain ampli-fier is not complicated by signals having a frequency which need not be corrected because of the resolution characteristics of the objective lens 17.
The FII corrector functions to sense the ab-solute value of a signal recovered from the video disc,~hich signal is known to suffer an amplitude change due to the resolution power of the objective lens 17 used in the video disc signal. This ~nown signal is then compared against a reference signal indicating the amplltude that the known signal should have. The out-put from the comparison is an indication Or the addi-tional amplification required for all of the signals lying in the frequency spectra affected by the resolv-lng power of the lens. The amplifier is designed to provide a variable gain over the frequency spectra.
Furthermore, the varlable gain is further selective based on the amplitude of the error signal. Stated another way for a first error signal detected between the signal recovered from the dlsc and the reference 3~ frequency, the variable gain ampllfler is operated at a first level of varlable ampliflcation over the entire frequency range of the affected signal. For a second level of error signal, the gain across the frequency spectra is ad~usted a different amount when compared _ . . .. , . _ . . _ ...

- 8~- 1151)B35 for the first color burst error amplltude signal.
~ eferring to Figure 17, there ls shol~n a block di~gram of the FM detector circuit 674 s hown with refer-ence to Fi~ure 14. The corrected frequency modulated slgnal from the FM corrector 672 ls applied to a limiter 720 over the line 675. The output from the limiter is applied to a drop-out detector and compen-sation circuit 722 over a line 724. It is the function of the limiter to change the corrected FM video signal lnto a discrlminated vldeo slgnal. The output from the drop-out detector 722 is applied to a lo~ pass filter 725 over a line 728. The output from the low pass fllter 726 is applied to a ~ide band vldeo dis-tribution amplifier 730 whose function is to provide a plurality of output si~nals on the line 66, 82, 134, 154, 156, 164 and 16;~, as previously described. The function of the FM detector is to change the frequency modulated video signal into a discriminated vldeo signal as shown with reference to llnes A and B of 20 Figure 18. The frequenc-y modulated vl~eo slgnal is ~ represented by a carrier frequency having carrier variations in time changing about the carrier fre-quency. The dlscriminated video slgnal is a voltage varying in time signal generally lying within the zero to one volt range suitable for display on the television monitor 98 over the line 166.
Referring to Figure 19, there ls shown a block diagram of the audio processing circuit 114. The frequency modulated videc signal from the distribution 3 amplifier 670 of the FM processing unit 32, as shown with reference to ~igure 14, applies one of lts inputs to an audio demodulator circuit 740. The audio demodu-lator clrcuit pro~ides a plurality o~ output signals, one of which is applied to an audio varlable controlled oscillator circuit 742 over a line 744. A first audio output is available on a line 74:~ for application to the audio accessory unit 120 an~ a second audio output signal is available on a llne 747 for application to the audio accessory unit 120 and/or the audio Jacks ~ ............ . . . ..

117 and 11~. The output from the audio voltage con-trolled oscillat`or is a 4.5 megahertz signal for appli-cation to the RF modulator 162 over the line 172.
Referring to Figure 20, there is shown a block dlagram of the audio demodulator circuit 740 shown with reference to Figure 19. The frequency modulated video signal is applied to a first band pass filter 750 having a central band pass frequency Or 2.3 mega-hertz, over the line 160 and a second line 751. The 10 frequenc~ modulated video sl~nal is applied to a second band pass filter 752 over the line 160 and a second line 754. The first band pass filter 750 strips the first audio channel from the FM video signal, appiies it to an audio FM discriminator 755 over a line 758. The 15 audio FM discriminator 755 provides an audio signal in the audio range to a switciling circuit 760 over a line 752.
The second band pass filter 752 having a central frequenc~r of 2.8 megahertz operates to strip the second au~io chann21 from the F~l video input signal - and applies this frequenc~ spectra of the total FM
si~nzl to a second video ~M discriminator 764 over a line 765. The second audio channel in the audio fre-quency range applied to the switching circuit 750 over a line 768.
The switching circuit 760 is provided with a plurality Or additional input signals. A first of which is the audio squelch signal from the tracking servo subsystem as applie~ thereto over the line 116.
3 The second input signal is a selection command signal from the function generator 47 as applied thereto over the line 170. The output from the switc~ling circuit is applied to a first amplifier circuit 770 over a line 771 and to a second amplifier circuit 772 over a 3~ line 773. The lines 771 and 773 are also connected to a summation circuit indicated at 774. The output from the summation circuit 774 is applied to a third ampli-fier circuit 7~5. The output from the first amplifier 770 is the c;lannel one audio signal for application to . ~

~ iS0835 -~4-the audio jack 117. The output rrom the second ampli-fier 772 is the second channel audio signal ror applicatlon tothe audio ~acl~ 118. The output from the thlrd amplirier 776 ls the audio signal to the audio VC0 742 over the llne 744. Referring brie~ly to Figure 21, there is shown on line A the frequenc~J
modulated envelope as recelved from the distribution amplifier in the FM processln~ unit 32. me output Or the audio F~ discriminator for one channel is shown on line ~. In this manner, the FM signal is changed an audio frequency signal for application to the s~iYitch-ing circuits 760, as previously descrlbed.
Xeferr~ng to Figure 22, there is shown a block diagram of the audio voltage controlled oscilla-tor 742 as shown with reference to Figure 19. Theaudio signal from the audio demodulator is applied to a band pass filter 780 over the line 744. The band pass filter passes the audio ~requency signals to a summation circui.t 782 by way of a pre-emphasis circuit 784 and a first line 786 and a second line 788.
The 3.58 megahertz color subcarrier frequency from the tan~ential servo system 80 is applied to a divide circuit 790 over tne line 140. The divide circuit 790 divides the color subcarrier frequency by 2048 and applies the output signal to a phase detector 792 over a line 794. The phase detector has a second input signal from the 4.5 megahertz voltage controlled oscillator circuit as applied to a second divide cir-cuit 798 and a first line 800 and 802. The divide 3 circuit 798 divides the output of the VC0 796 by 1144.
The output from the phase detector is applied to an amplitude and phase compensatlon circult 804. ~le output from the circuit 804 is applied as a third input to the summation circuit 782. me output from the voltage controlled oscillator 796 is also applied to a low pass filter 806 by the line 800 and a ~cond llne 808. The output from the filter 806 ls the 4.5 megahertz rrequency modulated signal for applicatlon to the RF modulator 182 by the line 172. The runction -85 1~ 835 Or the audio voltage controlled oscillator circuit is to prepare the audio signal received from the audio demod-ulator 7~0 to a frequency which can be applied to the RF modulato,~ 152 so as to be processed ~y a standard television receiver 95.
Referring briefl~- to Figure 23, there can be seen on line A a waveform representing the audio signal received from the audio demodulators and available on the line 744. Line ~ of Figure 23 represents the 4.5 megahertz carrier frequency. Line C of Figure 23 represents the 4.5 megahertz modulated audio carrier ~hich is generated in the VC0 circuit 796 for applica-tion to the RF modulator 152.
Referrlng to Figure 243 there ls shown a block diagram of the RF modul~tor 162 employed in the video disc player. The video lnformation signal from the FrV3 processing circuit 32 is applied to a DC re-storer 81~ over the line 154. The DC restorer 810 read~usts the blanking level of the received video Signal. The output from the restorer 810 is applied to a rirst b~lanced modulator 812 over a line 814.
The 4.5 megahertz modulated signal from the audio VC0 is appl ed to a second balanced modulator 816 over the~line 172. An oscillator circuit 818 functions to generate a suitable carrier frequency corresponding to one of the channels of a standard television re-ceiver 96. In the preferred embodiment, the Channel 3 frequency is selected. The output from the osclllator 818 ls applied to the first balanced modulator 812 over a line 820. The output from the oscillator 818 is applied to the second balanced modulator 816 over the line 822. The output from the modulator 812 is ap-plied to a summation circuit 824 over a line 826. The output from the second balanced modulator 816 is applied to the summation circuit 824 over the llne 828. ~eferring briefly to the wave~orm shown in Figure 25, line A shows the 4.5 megahertz ~requency modulated signal recelved rrom the audio VC0 over the line 172. Tine B o~ Figure 25 s}lows the video signal -8~- 115083~
received fro~ the FM processlng circuit 32 over the line 164~ The output from the summation circuit 824 is shcwn on line C. The signal shown on line C ls suitable for processing by a standard television re-ceiver. The signal shown on lil~e C is such as to causethe standard television receiver 96 to display the sequential fra~e lnformation as applied thereto.
Referring briefly to Figure 26, there is shown a video disc 5 having contained thereon a schematic 10 representation of an information track at an outside radius as represented by the numeral 830. An lnforma-tion track schematlcally shown at the inside radius is shown by the numeral 832. The uneven form of the information track at t.he outside radius demonstrates 15 an eY.treme degree of eccentricity arising from the effect of uneven cooling of the video disc 5.
Referring briefly to Figure 27, there is shown a schematic view of a video disc 5 having contained ,thereon an information track at an outside radius - 20 represented bJ the numeral 834. An informatlon track at an inside radius is represented by the numeral 836.
This Figure 27 shows the eccentricity effect of an off-center relationship of the tracks to a central aperture indicated generally at 838. More speclfically, 25 thé orf-center aperture effectively causes the distance represented by a llne 840 to be effectively dlfferent from the length of the line 842. Obviously, one can be larger than the ot~er. This represents the off-centered positlon of the center aperture hole 838.
~eferrlng t~ Figure 28, there ls shown a logic dlagram representing the first mode ~ operatlon of the focus servo 36.
The logic diagram sho~ln with reference to Figure 28 comprises a plurality of AND functlon gates 35 shown at 850, 852, 854 and 856. The AND function gate 850 has a plurality of input sign~ls, t~ne first of which is the r~N~ lFNA~L~ applied over a llne 858. The second lnput signal to the AND gate 850 ls the FOCUS
~IGNAL applled over a llne 860. The AND gate 852 has -87- 1~50835 a pluralit-y of input signals, the first of which ls the FOCUS SIG~JAL applied thereto for the line 860 and a second lil~- 862. The second lnput signal to the AND
runction gate 85~ is the lens enable slgnal on a line 5 8O4. The output from the AND function gate 852 is the ramp enable signal which is available for the entire period the ramp signal is being generated. The output rrcm the AND functlon gate 852 is also applied as an input signal to the AND function gate 854 over a line 10 8~6. The AND function gate 854 has a second input signal applied over the line 868. The signal on the line 868 is the FM detected signal. The output from the AND function gate 854 is the focus acquire signal.
m is rOcus acquire signal is also applied to the ramp generator 278 for disalbin~ the ramping waveform at that ~int. The AMD function gate 85S is equipped with a plurality of input signals, the first of which ls the FOCUS ~iGNAL applied thereto over the line 860 ,and an additional lire 870. The second input signal to the AND function gate 855 is a ramp and signal applied over a line 872. The output signal from the AND function gate 856 is the withdraw lens enabling signal. ~rie~lyJ the logic circuitry shown ~1ith refer-ence to Figure 28 generates the basic n~ode of operation of the lens servo. Prior to the function generator 47 generating a lens enable signal, the L~NS El~A~LE signal is applied to the AND function gate 850 along with the FOCUS SIGNAL. This indicates that the player is in an inactlvated condition and the output signal from the 3 AND runction gate indicates that the lens is in the fully withdrawn position.
~ hen the function generator generates a lens enable signal for application to the AND gate 852, the second input signal to the AND gate 852 indicates 35 that the video disc pla~Jer 1 is not in the focus mode.
Acccrdin~ly, the output si~nal 1'rom the AND gate 852 is the ramp enable signal which initiates the ramping waveform shown with reference to line P of Figure 6A.
The ramp enable signal also indicates that the focus -8s 1il50835 servo is in the acquire focus mode ~ operatlon and this enabling signal forms a rirst input to the AND
function gate 854. The second input signal to the AND
function gate 854 indicates ~hat FM has been success-fully detected and the output from the AND functlongate 854 is the focused acquire signal indicatit~ that the normal play mode has been successfully entered and frequency modulated video signals are being recovered from the surface of the video disc. The output from 10 the AND function &ate 856 indicates that a successful acquisition Or focus was not achieved in the first focus attempt. The ramp end signal on the lire 872 indicates that the lens has been fully extended towards the video disc surface. The FOCUS SIGI~AL on the line 15 870 indicates tilat focus was not successfully acquired.
Accordingly the output rrom the AND function gate 855 ~ithdraws the lens to its upper posit~on at which time a focus acquire operation can be reattempted.
Referring to Figure 29 there is sho"n a logic 20 diagram illustrating the additional mcdes of operation o~ the lens servo. A first AND gate 880 is equipped ~ith ~ plurallt~ of input signals the first of which is the focus signal generated by the AND gate 854 and applied to the AND gate 880 over a line 859. The 25 Fi~ DErrEcll SIGNAL is applied to the AND gate 880 over a line 882. The output from the AND gate 880 is applied to an OR gate 84 over a line 886. A second input signal is applied to th4 OR gate 884 over a line 888.
The output from the OR function gate 884 is applied to 30 a first one-shot circuit shown at ~90 over a line 892 to drive the one-shot lnto its state for generatlng an output signal on the line 894. Tl~e output signal on the line 894 is applied to a delay circuit 895 over a second line 898 and to a second AND function gate 900 35 over a line 902. The AND function gate 9CO is equipped with a second input signal on whic}l the FM detect signal is applied over a line 904. The output from the AND function gate 900 is applied to reset the first one-shot 890 over a line 905.

_... . ... . .. . .. .

~ 1150835 The output from the delay circuit 895 ls ap-plied as a first input signal to a third AND functio g~te 908 over a line 910. me AND function gate 908 is equipped with a second input signal which is the RAMP RE~ IGi~AL applied to the AND function gate 908 over a line 912. The output from the AND function gate 908 is applied as a first input signal to an OR circuit 914 over a line 916.
The output from the OR function gate 914 is the ramp reset enabling signal which is applied at least a fourth AND functlon gate 918 over a line 920. The second input signal to the AND f~lnction gate 918 ls the output signal from the first one-shot 890 over the line 894 and a second line 922. The output from the AND
function gate 918 is applied to a second one-shot cir-cuit 924 over a line 926. The output from the second one-shot indicates the timing period of t~le focus ramp voltage shown on line ~ of Figure 6A. The input signal on line 925 activates the one-shot 924 to generate its output signal on a line 928 for application to a delay circuit 930. The output from the delay circuit 930 forms one input to a sixth A~D function gate 932 over a line 934. The AI~D function gate 932 has as its second irput signal the ~OC~S SIGi~AL available on a line 936.
The output from the AND function gate 932 ls applied as the second input signal to the OR function gate 914 over a line 938. The output from the AND function gate 932 is also applied to a third ~e-shot circuit 940 over a line 942. The output from the third one-shot 3 is applied to a delay circuit 942 over a line 944. As previously mentioned, the output from the delay clrcuit 942 is applied to the OR function gate 8~4 over the line 888.
The one-sllot 890 is the circuit employed for 3~ generating the timing wavefor.m shown on lir.e D of Fi~ure ~. The second one-shG~ 92ll is employ-d ~or generatlng a waveform shown on liile E Or Flgure 6A.
The third one-shot 940 is employed for generating the waveform showA on llne F o~ Flgure 6A.

-~o -In one rorm of operation, the loglc clrcultry shown in F~ure 29 operates to delay the attempt to reac~uire rOcus due to momentary losses cr FM caused by imperfections on the video disc. This ls achleved in the following manner. The AND ~unction gate ~80 gener-ates an output signal on the line 885 only when the video disc player is in the rOcus mode and there is a temporary loss of FM as indicated by the Fi5 DETECT SIGNAL
on line 882. T'ne output signal on the line 885 triggers the first one-shot to generate a timin~ period Or pre-determined short length during which the video disc pl2yer will be momentarily stopped ~rom reattemptin~
to acquire lost ~ocus superricially lndlcated by the availability of the FM DEl~7~CT SI5NAL on the line 882.
The output rrom the first one-shot forms one input to the AND ~unction gate 900. If the FM detect signal available on 9~4 reappears prior to the timin~ out of the tlme period Or the ~irst one-shot, the output from the AND circuit 900 resets the ~irst one-shot 890 and 20 the video d'sc player continues reading the reacquired F~i signal. Assuming that the rirst one-shot is not reset, then the following sequence Or operatlon occurs.
The output from the delay circuit 895 is gated through the AND function gate 908 by the RAMP RESET SIGNAL
25 avallable on line 912. The RAMP ~ESET SIGNAL is avail-able ln the normal ~ocus play mode. The output from the AND gate 908 is applied to the OR gate 914 ~or gen-eratlng the reset signal causlng the lens to retrack and begin lts focus operatlon. The output rrom the OR
gate 914 is also applied to a turn on the second one-sllot whlch establishes the shape of the ramping wave~o~
shown ln Figure B. The output from the second one-shot 924 is essentlal coextensive in time with the ramping period. Accordingly, when the o~tput from the second one-shot is generated, the machine is caused to return to the attempt to acquire ~`ocus. I~en focus is success-~ùlly acquire~ tlle ~`OCU~ ~IGi~A~ on line 936 does not gate the output from the delay circuit 930 through to the OR function gate 914 to restart the automatlc focus .

procedure. HoweverJ when the video disc player does not acquire focus the FOCUS SIGNAL on line 935 gates the output from the delay circuit 930 to restart auto-matically the focus acquire mode. When focus is success-fully acquired, the output from the delay llne ls notgated through and the player continues ln its focus mode.
~ ile the invention has been partlcularly shcwn and described with reference to a preferred embod-iment and alteratlons thereto, it would be understood bythose skllled in the art that varlous changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims (4)

1. Apparatus for use in a signal recovery system for recovering a video signal from a video disc, wherein the signal includes liminance information, chro-minance information and periodic chrominance bursts having a prescribed amplitude, wherein the signal is recorded in a succession of light reflective and light non-reflective regions forming a plurality of substan-tially circular and concentrically arranged information tracks, and therein the system includes means for focus-ing a beam of radiation onto a selected track as the disc is rotated at a prescribed angular velocity and means for detecting a reflected beam of radiation hav-ing an intensity modulated by the recorded video signal, the gain of the higher frequency portion of the spectral response of the signal recovery system decreasing as the radius of the selected track decreases, thereby causing a corresponding variation in the respective amplitudes of the chrominance and luminance portions of the recov-ered video signal, said apparatus operating to correct for the variable gain of the system by controllably amplifying the corresponding portion of the frequency spectrum of the recovered video signal, said apparatus comprising:
means for detecting the amplitude of the suc-cessive chrominance bursts in the recovered video signal and for producing a corresponding control signal; and means for amplifying the video signal recov-ered from the disc, said control signal being coupled to said amplifying means to controllably adjust its gain for a frequency band corresponding to the higher fre-quency portion of the recovered video signal, thereby correcting for the variable gain of the signal recovery system.

2. Apparatus as defined in Claim 1, wherein:
the video signal recorded on the disc includes a carrier that is frequency modulated by a baseband luminance signal and a chrominance subcarrier, a substantially greater proportion of chrominance infor-mation than luminance information in the modulated signal being located in remote, lower sidebands; and the amplitude of the chrominance information in the reproduced frequency modulated video signal varies inversely with the radius of the selected track.

3. Apparatus as defined in Claim 2, wherein:
the relative lengths of the successive light reflective and light non-reflective regions forming each of the plurality of information tracks are sub-stantially directly proportional to the radius of the corresponding track; and the means for focusing a beam of radiation includes an objective lens having a limited resolving power that operates to decrease the spectral response of the signal recovery system as the relative sizes of the light reflective and light non-reflective regions decreases.

4. Apparatus as defined in Claim 1, further including means for allowing a manual adjustment of the gain of said amplifying means in the region of said higher frequency portion of the signal spectrum.