MXPA97002229A - Apparatus and method for monitoring monitoring - Google Patents

Abstract

The present invention relates to a radiant energy beam control apparatus, wherein the beam detector has first and second outputs sensitive to the position of the beam. A circuit is coupled to the outputs of the detector to produce an error signal representing a displacement of the beam from a predetermined position, in which the error signal has a periodic characteristic in relation to the displacement. A servomechanism sensitive to the error signal resets the shifted beam to a predetermined position. A local feedback loop is coupled to the outputs of the detector and includes a first and second periodic function generators, each sensitive to the error signal. The second periodic function generator has an output that differs from an output of the first periodic function generator by a phase angle, preferably 90ø. A first multiplier multiplies the first output of the detector by the output of the first periodic function generator. A second multiplier multiplies the second output of the detector by the output of the second periodic function generator. wherein the outputs of the first and second multipliers are provided as circuit inputs to modify the err signal

Description

APPARATUS AND METHOD FOR MONITORING MONITORING DESCRIPTION OF THE INVENTION This invention relates to arrays for tracking control for optical disk drives. More particularly, this invention relates to an improved servo control (servo control) which extends to the operating range of a closed circuit mode of operation of a tracking servomechanism to a plurality of information tracks on a disk. In the optical disk units in which the information is stored in a plurality of spiral or concentric information tracks, a fixation of a recording beam or reproduction of a track of information of interest is commonly maintained by a tracking servomechanism, for example. For example, the servomechanism described by Cesh Ovsky et al. , U.S. Patent No. 4,332,022. The tracking servomechanism responds to minimize the tracking error signal Vp derived from the intensity of the reflected light beam returning from the optical disc medium and which is given by the equation: REF: 24311 VP = A sine. { 2tt? where A is a constant, - x is the displacement of the beam from the center of the track, - and p is the track separation. It is often necessary to quickly move the recording or playback beam in the radial direction of the disc from a first information track to a second information track. Although this can be done by opening the servo circuit, it is undesirable for reasons of damaged stability of the tracking system, and because time is lost when acquiring fixation in a new information track. Consequently, the art has attempted to find ways to maintain the closed circuit operation of a servomechanism while shifting the light beam from a first region of interest to a second region of interest. In U.S. Patent No. 4,779,251 for Burroughs, an arrangement is described in which the circuits generate a ramp waveform that is used to introduce a controlled deviation into a tracking servomechanism. The servomechanism error signal, which is derived from the characteristics of the preformed fine tracking, is inverted in phase when the reading beam moves between tracks. The ramp waveform is adjusted according to the tracking error information memorized from previous micro-highs between tracks. It is a main object of the present invention to extend the range of operation of a tracking servomechanism, to operate in a closed circuit mode, beyond the range of a quarter track or a conventional means. It is another object of the invention to improve the operation of the tracking servomechanism and the response to disc, noise, shock and vibration defects. These and other objects of the present invention are obtained in an optical disk drive by providing an optical socket having a plurality of outputs to produce an error signal that supplies a servomechanism cycle. The error signal also supplies a local feedback circuit which includes a plurality of sine-function generators when modifying the outputs of the optical socket, so that the tracking error signal plotted against the radial position of the reading beam is transforms from a sinusoidal waveform into a substantially linear ramp. The operating range of the ramp extends over two or more information tracks on the disk. The local feedback circuit is independent of the main tracking servomechanism circuit, although it can be designed to share some components. In addition to the sine function generators, the local feedback circuit comprises two multipliers, an amplifier that adds up the differences, a local circuit gain element and a phase compensator, and an additive circuit to add a phase shift value to one of two sine function generator inputs. The invention provides an apparatus for controlling a beam of radiant energy, wherein a beam detector has first and second outputs sensitive to a beam position. A circuit is coupled to the outputs of the detector to produce an error signal representing a displacement of the beam from a predetermined position, in which the error signal has a periodic characteristic in relation to the displacement. A servomechanism sensitive to the error signal resets the beam to the predetermined position. A local feedback circuit is coupled to the outputs of the detector, and includes a first and second periodic function generator, each sensitive to the error signal. The second periodic function generator has an output that differs from the output of the first periodic function generator by a phase angle, preferably 90 °. A first multiplier multiplies the first output of the detector by the output of the first periodic function generator. A second multiplier multiplies the second output of the detector by the output of the second periodic function generator, in which the outputs of the first and second multipliers are provided as circuit inputs to modify the error signal. In one aspect of the invention, the periodic characteristic is substantially sinusoidal, and the first periodic function generator and the second periodic function generator are sine generators. Preferably, the first and second outputs of the detector have an approximate mutual quadrature relationship with respect to the beam shift, and the phase angle is about 90 °. The phase angle may be in a range from about 60 ° to about 120 °. The detector may include an intermetrometer. The invention provides a method for controlling the beam of radiant energy. It is performed by generating first and second sensing signals sensitive to a beam position; producing an error signal representing a displacement of the beam from a predetermined position, in which the error signal has a characteristic "periodic in relation to the displacement; resetting the beam moved to the predetermined position in response to the error signal; and generating a first and second periodic signals The second periodic signal differs from the first periodic signal by a phase angle which is preferably 90. The error signal is produced by multiplying the first detection signal by the first Periodic signal to provide a first product signal, multiply the second detection signal by the second periodic signal to provide a second product signal, and determine the difference between the first product signal and the second product signal. tracking control for an optical disk system, a source directs a beam of radiant energy towards a selected track of an optical disc. There are means for imparting relative rotational movement between the beam and the disk about an axis of rotation, a beam targeting means for moving the beam in a generally radial direction relative to the disk, so that the beam follows a track of information selected A detector is sensitive to the radiant energy returning from the selected information track and has a first output signal and a second output signal, in which the first output signal differs in phase from the second output signal according to a displacement of the beam from the selected bar. A first multiplier has a first input electrically applied to the first output signal of the detector. A second multiplier has a first input electrically coupled to the second output signal of the detector. A difference adding amplifier has a first input coupled to an output of the first multiplier and a second input coupled to an output of the second multiplier to generate an error signal. A first periodic function generator has an input coupled to an output of the difference adding amplifier and an output coupled to a second input of the first multiplier. A second periodic function generator has an input coupled to an output of the difference adding amplifier and an output coupled to the second input of the second multiplier. A servomechanism is responsive to the difference output of the amplifier amplifier to operate the beam addressing means. In one aspect of the invention, a circuit gain amplifier coupled to the output of the difference adding amplifier that generates an amplified error signal A of the feedback loop compensation circuit coupled to the cycle gain amplifier is provided. of phase gain for the amplified error signal. There is a phase shifter coupled to the cycle compensation circuit and which is coupled to both the first periodic function generator and the second periodic function generator, wherein the phase shifter provides a predetermined voltage deviation to the error signal. The invention provides a method for tracking control in an optical disk system, it is carried out by directing a beam of radiant energy towards a selected track of a plurality of information tracks of an optical disk, imparting relative rotational movement between the beam and the disk around an axis of rotation, moving the beam in a generally radial direction relative to the disk to follow the selected information track, and detecting radiant energy returning from the selected information track. A first output signal and a second output signal are generated, in which the first output signal differs in phase from the second output signal according to the displacement of the beam from the selected track. The method additionally includes multiplication of the first output signal by a first periodic function of an error signal to provide a first product, multiply the second output signal by a second periodic function of the error signal to provide a second product, subtract the first product from the second product to produce an error signal and direct the beam to the selected information track according to the error signal. For a better understanding of these and other objects of the present invention, reference is made to the detailed description of the invention, by way of example, which can be read together with the following drawings, in which: Figure 1 is a schematic diagram of an apparatus according to the invention, - Figure 2 is a fragmentary view of the surface of an optical recording medium with tracks, - Figure 3 is a block diagram of a signal recovery subsystem in the apparatus from figure l; Figure 4 is a diagram illustrating additional details of the subsystems shown in Figure 3, - Figure 5 is a spatial plot of a signal waveform corresponding to the tracks on an optical medium, - Figure 6 is an electrical diagram of a portion of the apparatus shown in Figure 1; Figure 7 is a block diagram of the generator of the sine function; Figures 8 and 9 are electric waveforms which are useful for understanding the invention, - Figures 10 and 11 are schematic diagrams illustrating a particular embodiment of the invention, - Figure 12 illustrates a ring detector for use in the embodiment of Figures 10 and 11; Figure 13 is an electrical diagram of a preferred embodiment of the invention, - Figure 14 is a detailed electrical diagram illustrating the function generator shown in the scheme of Figure 13; and Figure 15 is a detailed electrical diagram illustrating circuit synchronization circuits shown in Figure 13. Figure 1 shows an optical system 10 of a disc player for information media such as video discs. , magneto optical discs, audio discs and computer data discs, collectively referred to herein as an "optical disc". The optical system 10 includes a laser 18 used to generate a reading beam 22 which is used to read a coded signal, stored on an optical disk 26, a first lens 28, a diffraction grating 30, a prism 34 divides beam beam and a quarter wave plate 38. The optical system 10 additionally includes a mirror 42, and a slow target 54 having an entrance aperture 58. The beam reaching the optical disk 26 can be moved in a radial direction by known beam moving means, symbolically indicated by the inductor 52. In practice, the inductor 50 is controlled by a tracking servomechanism 94. In figure 2 , an enlarged portion of the optical disk 26 is shown. The optical disk 26 includes a plurality of information tracks 66 formed on a surface 70 presenting information. Each information track 66 comprises a succession of light reflecting regions 74 and light non-reflecting regions 78. The light reflecting regions 74 have highly polished, generally planar surfaces, such as a thin aluminum layer. The non-light reflecting regions 78 are generally surfaces that scatter light and appear as highlights or elevations above the planar surface that represent the light reflecting regions 74. The reading beam 22 has one or more degrees of movement with respect to the surface 70 having information of the optical disc 26, one of which in the radial direction, as indicated by the arrow 82 with two tips. The reading beam 22 generated by the laser 18 first passes through the first slow 28, which is used to shape the reading beam 22 to have a size which fully satisfies the entrance aperture 58 of the objective lens 54. After the reading beam 22 is suitably shaped by the first lens 28, it passes through the diffraction grating 30 which divides the reading beam 22 into three separate beams (not shown). Two of the beams are used to develop a radial track error signal, and the other is used to develop both a focus error signal and an information signal. The three beams are treated identically by the remaining portion of the optical system. Therefore, they are collectively referred to as the reading beam 22. The output of the diffraction grating 30 is applied to the beam splitting prism 34. The axis of the prism 34 is slightly offset from the path of the reading beam 22, the reasons for which are explained more fully in the US patent No. Re. 32,709, granted on July 5, 1988, the entire text of which it is incorporated herein by reference.

The transmitted portion of the reading beam 22 is applied through the plate 38 of the quarter wave which provides a deviation of 45 ° in the polarization of the light forming the reading beam 22. The reading beam 22 then strikes the mirror 42 which redirects the reading beam 22 towards the objective lens 54. The function of the servomechanism subsystem 94 is to direct the point of incidence of the reading beam 22 on the surface 70 presenting information of the optical disk 26 so as to follow radially the indicators that present information on the surface 70 of the optical disk 26. This is it performs by urging the inductor 52 to respond to an error signal, so that the point of incidence of the reading beam 22 is directed to a desired position in a radial direction on the surface 70 of the optical disk 26, as shown in FIG. indicated by the arrow 86 shown in Figure 2. After the reading beam 22 is reflected from the mirror 42, as the reflected beam 96, it impinges on the entrance aperture 58 of the objective lens 54 and is focused as a point on one of the tracks 66 presenting information of the optical disc 26 by the lens 54. The objective lens 54 is used to conform the reading beam 22 to a point of light having the desired size in the point at which the reading beam 22 impinges on the surface 70 presenting information of the optical disc 26. It is desirable to present a reading beam 22 which has the inlet opening 58 completely as this results in a high light intensity in the point of incidence with the disk 26. The optical system 10 therefore directs the reading beam 22 to the optical disk 26 and focuses the reading beam 22 downwards -to a position at an incident point with the optical disk 26. In In the normal reading mode, the focused reading beam 22 impinges on the light reflecting regions 74 and the non-reflective light regions 78, successively positioned representing the information stored in the disk 26. The reflected light is recovered by the lens 54 to generate a reflected portion of the reading beam. The reflected beam 96 returns to be directed by the same path previously explained by striking, in sequence, on the mirror 42 and the quarter-wave plate 38, which provides an additional polarization deviation of 45 ° resulting in a cumulative total 180 ° polarization deviation. The reflected reading beam 96 then impinges on the beam deflection prism 34 which deflects a portion of the reflected reading beam 98 to strike a portion of the signal recovery subsystem 104, which is shown in Figure 3. Figure 3 shows a schematic block diagram of a portion of the signal recovery subsystem 104. The signal recovery subsystem 104 receives the beam 98 and generates a plurality of information signals. Then these signals are provided to different portions of the optical disc player. These information signals are generally found in two types, a signal of information itself which represents the information stored and a control signal derived from the information signal to control the various parts of the optical disc player. The information signal is a modulated signal representing the information stored on the disk 26 and is provided to a signal processing subsystem (not shown). A first type of control signal generated by the signal recovery subsystem 104 is a differential focusing error signal which is provided by a focusing servomechanism system (not shown). A second type of control signal generated by the signal recovery subsystem 104 is a differential tracking error signal. The differential tracking error signal is provided to the tracking servomechanism subsystem 94 to drive the inductor 52 for radial displacement of the read beam 22. To receive the reflected beam 98, the signal recovery subsystem 104 includes a diode detector array 108 that includes a first tracking photodetector 112, a second tracking photodetector 116, and a concentric ring detector 120 having both an inner portion 122 and an outer portion 123 . This signal recovery subsystem 104 additionally includes a first tracking preamplifier 124, a second tracking preamplifier 128, a first focusing preamplifier 132, a second focusing preamplifier 136, a first differential amplifier 140 and a second differential amplifier 144 . The first and second tracking preamplifiers 124 and 128, together with the first differential amplifier 140, constitute a tracking signal processing portion 146 of the signal recovery subsystem 104. The diode detector array 108 has first, second, third and fourth outputs 148, 152, 156 and 160. The first output 148 is electrically connected to an input 164 of the first tracking preamplifier 124, the second output 152 is electrically connected. at an input 168 of the second tracking preamplifier 128, the third output 156 is electrically connected to an input 172 of the first focusing preamplifier 132, and the fourth output 160 is electrically connected to an input 176 of the second focusing preamplifier 136. The first tracking preamplifier 124 has an output 180 which is electrically connected to a first input 182 of the first differential amplifier 140 while the second tracking preamplifier 128 has an output 184 which is electrically connected to a second input 186 of the first amplifier 140 differential. The first focusing preamplifier 132 has an output 188 which is electrically connected to a first input 190 of the second differential amplifier 144 while the second focusing preamplifier 136 has an output 192 which is electrically connected to a second input 194 of the second amplifier. 144 differential. The reflected beam 98 comprises three portions: a first tracking beam 196 which impinges on the first tracking photodetector 112, a second tracking beam 197 which impinges on the second tracking photodetector 116; and a central information beam 198 which impinges on the concentric ring detector 120. The signal predicted by the first tracking photodetector 112 is provided to the first tracking preamplifier 124 via the first output 148 of the diode detector array 108. The signal predicted by the second tracking photodetector 116 is provided to the second tracking preamplifier 128 by means of the second output 152 of the diode array 108. The signal produced by a lower portion 122 of the concentric ring detector 120 is provided to the first focus preamplifier 132 by means of the third output 156 of the diode array 108 while the signal produced by the outer portion 123 of the ring detector 120 concentric is provided to the second preamplifier 136 via the fourth output 160 of the diode array 108. The output from the first differential amplifier 140 is a differential tracking error signal which is applied to the tracking servo system 94 which is describes in more detail in the following. The output of the second differential amplifier 144 is a differential focus error signal which is applied to a focusing servomechanism system (not shown). Although the invention of the first application is described with reference to the signal recovery subsystem 104 just described, it can also be used with other signal recovery subsystems known in the art. The function of the tracking servomechanism subsystem 94 is to direct the incidence of the beam 22 so that it directly impacts the center of the information track 56. The reading beam 22 generally has the same width of the sequence that presents information of indicators which form the information track 66. Therefore, the maximum signal recovery is obtained when the reading beam 22 is caused to travel so that all or most of the beam 22 impinges on the light reflecting and non-reflecting regions 74 and 78, placed successively, of the information track 66. The follow-up servomechanism subsystem 94 is sometimes referred to as the radial tracking servomechanism because the deviations of the higher power information track 66 are presented in the radial direction on the surface 70 of the disk. The radial tracking servomechanism 94 is generally operable continuously in the normal reproduction mode of the optical disc player. The tracking servomechanism subsystem 94 is shown in greater detail in FIG. 4 and includes a cycle interruption switch 200 and an amplifier 202 for driving the inductor 52. The cycle switch switch 200 receives the tracking error signal from the signal recovery subsystem 104 in the first input 204 and receives a signal and cycle interruption in a second input 206. When the cycle interruption is not active, the tracking error signal is provided in its output 208. The amplifier 206 receives the inserted tracking error signal 210 and generates a tracking signal A for the inductor 52 on the first output 202 and a tracking output B for the inductor 52 on the second output 214. Together, the tracking signals A and of tracking B control the radial displacement of the reading beam 22. When the tracking error signal is destroyed and the input 210 of the amplifier 202, the two tracking signals control the current through the inductor 52 so that the reading beam 22 incident thereon moves in the radial direction and it is centered on the information track illuminated by the reading beam 22. The direction and amount of movement depends on the polarity and amplitude of the tracking error signal. In certain modes of operation, the tracking servomechanism subsystem 94 is interrupted so that the tracking error signal generated by the signal recovery subsystem 104 is not provided to the amplifier 202. One such mode of operation deserves the operation of search, when it is desired to have the reading beam 22 focused radially transversely to a portion of the portion presenting information of the disk 26. In such an operation mode, an interruption signal is provided at the second input 206 of the switch switch 200 and to the tracking servodrive system 94, which causes the switch 200 to prevent a tracking error signal from being provided at its output 208. Furthermore, in the kickback operation mode, in which the beam is caused to of focused reading jumps from a track to an adjacent track, a tracking error signal is not provided to the amplifier 202. In the mode of abrupt recoil operation, the amplifier 202 does not provide tracking signals A and tracking B, as it would tend to destabilize the deflection means of the radial beam symbolized by the inductor 52, and requires a longer period of time for the subsystem 94 of radial tracking servomechanism regain proper tracking of the next adjacent information trail. Usually, in an operation mode in which the tracking error signal is removed from the amplifier 202, a substitute pulse is generated to provide an unambiguous and clear signal to the amplifier 202 to disguise the reading beam 22 to its next assigned position. A cross-sectional view taken in the radial direction through the optical disk 26 is shown on line A of FIG. 5, which shows both the plurality of information tracks 66 and the plurality of inter-track regions 224. Interstate regions 224 are similar to light reflective regions 74, which are shown in Figure 2. The latitudes of lines indicated as 228 and 232 show in center-to-center separation between a central track 236 and a first adjacent track 240. and the central track 236 and a second adjacent track 244, respectively. A point indicated with the number 248 on line 228 and a point indicated with number 252 on line 232 represent the crossing points between the central track 236 and the adjacent tracks 240 and 244, respectively. The crossing points 248 and 252 each are exactly halfway between the central track 236 and the first and second tracks 240 and 244. A point indicated by the number 256 on line 228 represents the center of the first information track 240. , while a point indicated with the number 260 on line 232 represents the center of the second information track 244. A point indicated with the number 264 represents the center of the central information track 236. A typical optical disk contains approximately 4,331 information tracks per cm (11,000 tracks of information per inch). The distance from the center of an information track to the next adjacent information track is in the range of 1.6 microns, while the information indicators aligned in a particular information track have a width of approximately 0.5 microns. This leaves approximately 1 miera of empty and open space between the outermost regions of the indicators placed on adjacent information tracks. When the reading beam 22 is scattered or diffused from the center of. the information track 66, the reflected signal received by the first tracking photodetector 112 or the second tracking photodetector 116 iases in intensity while the reflected signal received by the other tracking photodetector decreases in intensity. The fact that a photodetector receives a more or less intense signal depends on the direction in which the reading beam 22 is dispersed from the center of the information track 66. The phase difference between the signals provided from the first and second tracking photodetectors 112 and 116 represents the tracking error signal. The tracking servomechanism subsystem 94 receives signals from the first and second tracking photodetectors 112 and 116 and acts to minimize the difference between them and thus have the reading beam 22 centered on the information track 66.

The differential tracking error signal generated in the first differential amplifier 140 is shown in line B of FIG. 5, and is a representation of the radial position of the reading beam 22 on the disk 26. The error signal output of differential tracking has a first maximum tracking error at a point indicated with the number 268 in which it is intermediate to the center of the central information track 236 and the crossing point 248 and a second maximum tracking error at a point indicated with the number 272 which is intermediate to the central part of the central information track 236 and the crossing point 252. A third maximum tracking error is displayed at the point indicated with the number 276 which is intermediate to the center of the first information track 240 and the crossing point 248, and a fourth maximum tracking error is shown at a point indicated with the number 280 which is intermediate to the center of the second information track 244 and the crossing point 252. Minimal tracking errors are shown at indicated points with 284, 288 and 292 that correspond to the center of the information tracks 240, 236 and 244, respectively. Minimal tracking errors are also shown as points indicated by numbers 296 and 298 that correspond to crossing points 248 and 252, respectively.

In Figure 6 a tracking signal processing portion 300 of the signal processing subsystem 104 of the present invention is shown. The tracking signal portion 300 receives tracking error signals for both the first tracking photodetector 304 and the second tracking photodetector 308 of a diode array 312 similar to the diode array 108 described with reference to FIG. 3. Although not shown, the processing portion 300 may receive tracking error signals from other types of photodetector is such as a double photodetector. The tracking signal processing portion 300 includes a first preamplifier 316, a second preamplifier 320, a first operational amplifier 324, a second operational amplifier 328, a first analog multiplier 332, a second analog multiplier 336 and an add amplifier 340. The tracking signal processing portion 300 additionally includes a local feedback loop 344 comprised of a third operational amplifier 348, a feedback loop compensation circuit 352, a phase shifter 356 and a first and second generators 360 and 364 of breast respectively. The phase shifter 356 provides a deviation voltage which results in a phase deviation between the outputs of the generators 360, 364 of the sine function. The first preamplifier 316 has an input 368 and an output 372, and the second preamplifier 320 has an input 376 and an output 380. The first operational amplifier 324 has a first positive input 384 which is electrically connected to the output 372 of the first preamplifier 316, a second negative output 388 which is electrically connected to a positive voltage source 392, and an output 396. The second operational amplifier 328 has a first positive input 400 which is electrically connected to the output 380 of the second preamplifier 320, a second negative input 404 which is electrically connected to the voltage source 392 and an output 408. With reference to the feedback portion 344 of the tracking signal processing portion 300, the third operational amplifier 348 has an input 412 and an output 416. The phase compensation circuit 352 has an input 420 which is c electrically connected to the output 416 of the third operational amplifier 348 and to an output 424. The phase shifter 356 has an input 428 which is electrically connected to the output 424 of the phase compensation network 352 and to an output 432. The first generator sine function has an input 436 which is electrically connected to the output 432 of the phase shifter 356 and has an output 440, while the second sine function generator 364 has an input 444 which is electrically connected to the output 424 of the phase compensation network 352 and has an output 448. The first analog multiplier 332 has a first input 452 which is electrically connected to the output 396 of the first operational amplifier 324, a second input 456 which is electrically connected to the output 440 of the first sine function generator 360 and an output 460. The second analog multiplier 336 has a first input 464 which is electrically connected to the output 408 of the second operational amplifier 238, a second input 468 which is electrically connected to the output 448 of the second generator 364 of the sine function and an output 472. The adding amplifier 340 has a first input 476 which is electrically connected to the output 460 of the first analog multiplier 332, a second station 480 which is electrically connected to the output 472 of the second analog multiplier 336 and to an output 484 which is electrically connected to both the input 412 of the third operational amplifier 348 and the tracking error subsystem 94. The first preamplifier 316 receives a tracking signal output from the first tracking photodetector 304 at its input 368 while the second preamplifier 320 receives a tracking signal output from the second tracking detector 308 at its input 376. Both tracking signals they are periodic signals when plotted as a function of the radial position along the surface of the disc 26, and the two signals are out of phase approximately 90 °. The output of the tracking signals from the two tracking sensors 304 and 308 are each amplified and then provided at the outputs 372 and 380 of the first and second preamplifiers 316 and 320, respectively. The first operational amplifier 324, which receives the amplified tracking signal from the first amplifier 316 at its positive input 384 and receives a positive voltage at its negative input 388, removes the common voltage mode from the tracking signal and provides a portion larger signal of the signal corresponding to the tracking error signal at its output 396. The second operational amplifier 328, which receives the amplified tracking signal from the second preamplifier 320 at its positive input 400 and receives a positive voltage at its negative input 404, removes the common mode voltage from the tracking signal and provides a greater proportion of the signal corresponding to the tracking error signal at its output 408. The first multiplier 332 multiplies the received tracking signal from the output 396 of the first amplifier 324 • operational with a feedback signal received from the output 440 of the first 360 generator of sine function. The resulting modified tracking signal is provided at the output 460 of the multiplier 332. The second multiplier 336 multiplies the tracking signal received from the output 408 of the second operational amplifier 328, with a feedback signal received from the output 448 of the second generator 364 of the sine function. The resulting modified tracking signal is provided at the output 472 of the multiplier 336. The adding amplifier 340 receives the modified tracking signals from the first and second multipliers 332 and 336 at their first and second inputs 476 and 480, respectively. Upon receiving these signals, the adding amplifier 340 adds them algebraically to generate a differential tracking error signal representing the phase difference between the two modified tracking signals. The differential tracking error signal is provided at the output 484 of the amplifier 340. The tracking error signal is then provided to the interruption switch 200 of the motion servomechanism subsystem 94 (FIGS., 4) as well as to the feedback portion 344 of the tracking signal processing portion 300. The feedback portion 344 of the tracking signal processing portion 300 receives the differential tracking error signal at the first input 412 of the third operational or feedback amplifier 348. The feedback amplifier 348 amplifies the tracking error signal using a predetermined cycle gain and provides the amplified signal to the input 420 of the feedback loop compensation circuit 352. The feedback loop compensation circuit 352 provides a phase gain compensation for the amplified tracking error signal and provides the signal to both the input 444 of the second sine generator 364 and the input 436 of the phase shifter 356. The phase shifter 356 provides a predetermined voltage deviation to the tracking error signal received at its input 428 so that the signal provided at the input 436 of the first generator 360 of the sine function differs from the signal provided at the input -444 of the second generator 364 of the sine function at a predetermined voltage. The voltage deviation introduced in the phase shifter 356 is selected to have a value that causes the output of the two generators 360 and 364 of the sine function to be 90 ° out of phase. The effect of this phase shift is that the signal provided at the output 440 of the first generator 360 of the sine function is the same as that which would be provided by a cosine generator if it were to operate on the signal provided at the output 424 of the phase compensation network 352. Therefore, the signal output from the first and second sine function generators 360 and 364 are out of phase by 90 °. Although a phase difference of substantially 90 ° is preferred, the invention can be carried out with other phase differences as well, within a range of about 30 °. Therefore, the phase angle can be in a range of about 60 ° to about 120 °. Without the phase difference of the signals at outputs 440, 448 is too large, the system can become unreliable.

Both the first and second sinus function generators 360 and 364 can be implemented in various ways well known in the art. One such implementation is shown in Figure 7, which shows a sine function generator consisting of an analog-to-digital converter 488, a read-only memory search table 490 having a plurality of stored sine values and a converter 492 from digital to analog. The signal provided at the input of the sine function generator is first converted to a digital signal by the converter 488, the read-only memory 490 receives this digital signal at its input 494 and generates a corresponding sine function value at its output 496. The sine function value is converted to an analog signal by the converter 492 and the output of the sine function generator is provided. The signal recovery subsystem 104 (FIG. 3), when operating with the tracking signal processing portion 300 of the present invention, continues to provide a tracking error signal to the tracking servomechanism subsystem 94 (FIGS. 1, 4) . The follow-up servomechanism subsystem 94 uses the tracking error signal to control the radial position of the reading beam 22 when driving the inductor 52 in the same manner as described above, therefore, the servo subsystem 94 of tracking operates to keep the reading beam 22 centered on the information track 66. Although the tracking servomechanism subsystem 94 uses the tracking error signal provided in the same manner regardless of the tracking signal processing portion used in the signal recovery subsystem 104, the use of the signal processing portion 300 of tracking results in that a different tracking error signal is provided to the tracking servomechanism subsystem 94. The tracking error signal provided when the tracking signal processing portion 300 is used remains periodic, but the use of the portion 300 causes each period of the tracking error signal to represent a greater range of positions on the disk 26 optical. Figure 8 shows a comparison of the tracking error signals, each of which is a function of the radial position, with respect to a portion of the disk 26. A signal 512 is the tracking error signal generated by the subsystem 104 signal recovery using the tracking signal processing portion 146 of the prior art, while a signal 516 that is in the tracking error signal generated by the signal recovery subsystem 104, which uses the 300 portion signal processing processing of the present invention. Because the tracking error signal 516 is substantially linear in the region where its values are close to zero, that is, half between its extremes, it can be said that the tracking signal processing portion 300"linearizes" "the tracking error signal. However, the signal 516 remains periodic, as can be seen in Figure 9, which shows the value of the signal 516 over a larger portion of the disk 26. When the tracking signal processing portion 146 is used, each period of the tracking error signal 512 represents a track 66 of information of the disc 26. However, when the tracking signal processing portion 300 is used, each period of the tracking error signal may be elaborated to represent any number of information tracks 66. The number of information tracks 66 represented by each period of the tracking error signal 516 is determined by the gain of the feedback amplifier 348. There are advantages to "linearizing" a large number of tracks 66. For example, after the local feedback cycle 344 operates to linearize tracking error characteristics on several tracks, a noise pulse with a magnitude greater than one track is still within the range of operation of the negative slope of the linearized error signal, which allows a normal response by the tracking error subsystem 94 to such a noise pulse. However, because the amplitude of the signal 516 is infinite, the greater the number of tracks 66 represented in each period, the smaller the difference in voltage between each of the tracks 66 will be. If the voltage difference between the tracks 66 adjacent is too small it can be difficult to differentiate between tracks, and tracking errors can result. Therefore, there is an equilibrium or compensation in the operation that must be carried out when choosing the number of tracks that are represented for each period of the tracking error signal 516. The tracking servomechanism 94 must operate within the negative feedback slope of the tracking error signal 516. This is because in the event that a positive tracking error signal is provided, the tracking servomechanism 94 would be driven by the inductor 52 so as to move the beam 22 in a direction that would cause the tracking error to increase . The tracking error would continue to accumulate, which would cause a malfunction. This is also valid with respect to the response of the tracking servomechanism to the tracking error signal 512. Within the feedback portion 344 of the tracking signal processing portion 300, however, the use of positive feedback does not increase any such problems. This is because the tracking processing portion 300 is self-correcting so that it is always set to a negative slope of the tracking error signal 516, regardless of whether a positive feedback signal was initially provided. The values of the tracking signals provided by the first and second tracking photodetectors 304 and 308, taken together, represent a relative radial position of the reading beam 22 on the disk 26. In addition, the value of the signal provided to the portion 344 of feedback of the processing portion 300 of 3 tracking signal represents a relative radial feedback position. The use of the feedback portion 344 minimizes the difference between the values of these two signals. Therefore, the tracking signal processing portion 300, while using the feedback portion 344, is capable of resetting the tracking error signal to zero, a value representing a particular radial position on the disk 26. This allows that the follow-up servomechanism subsystem 94 stabilizes the reading beam 22, which impinges on the desired information track 66. The signals provided by the first and second tracking photodetectors 304 and 308 are both periodic and are approximately 90 ° out of phase. They can be represented by the sine and cosine functions. For the purposes of the following description, the assumption is made that the photodetector has two quadrature signal outputs. The signal provided by the first tracking photodetector 304 to the first preamplifier 306 is defined as sin (x) and the signal provided by the second tracking photodetector 308 to the second preamplifier 320 is defined as sin (x + 90) or eos (x) , where x is the relative radial position of the reading beam 22. The signal provided in the second input 468 of the second multiplier 336 is defined as sin (y), and the signal provided in the second input 456 of the first multiplier 332 is defined as sin (y + 90) or eos (y), in the that y is the value of the relative radial feedback signal. Given these definitions, the signal at the output 460 of the first multiplier 332 is sin (x) eos (y) and the signal at the output 472 of the second multiplier 336 is eos (x) sin (y). Thus, the signal at the output 484 of the adding amplifier 340 is: a [sin (x) eos (y) -eos (x) sin (y)] = a sin (x-y) «a (x-y) (2) where a is a constant gain factor. As is known in the art, for values of x-y close to zero, sin (x-y) is approximately x-y. Therefore, for values of x-y close to zero, the tracking error signal, a (sin (x-y)) is substantially linear. The ratio of x and y can be adjusted for a given application by appropriate adjustments of the gain of the feedback amplifier 348. In a specific embodiment of the present invention, the second sine function generator 364 can be replaced by a cosine function generator, which receives the signal provided at the output 424 of the phase compensation network 352. The use of the cosine function generator in this mode eliminates the need for the use of a phase shifter 356. Now, with reference to Figures 6, 10, 11 and 12, in a specific embodiment of the invention, the inputs to the preamplifiers 316, 320 are developed by an optical pickup link which includes an optical subsystem, represented here by the prism 520. A source beam 524 is passed through a lens 526, and is received by the conventional interferometer 528 having a plate 529 to separate the source beam into two beams, 530 and 532, which are reflected from the mirrors 534, 536, respectively. The prism 520 and a portion of the interferometer 528 are movable relative to one another in the directions indicated by the double-headed arrow 522. As a consequence of the relative movement of the same, the periphery patterns developed by the interferometer vary. The reflected beams are recombined as the beam 528, which is collimated by a lens 540. The beam 538 then reaches the receiver / analyzer 542. The periphery patterns transmitted in the beam 528 are measured by a quadrature photodetector 546, which it may be a ring photodetector and which is usually placed inside the receiver / analyzer 542. Analog outputs 548, 550 of the photodetector 546 are then presented to the preamplifiers 316, 320 (Figure 6). With reference again to FIGS. 1 and 3, it has been described in the foregoing that the modalities described above result in an error signal, for the servomechanism circuit; however, in certain applications, where only the position or other characteristic of an object is desired to be measured, the error signal produced by the signal processing portion 146 need not be provided to a servomechanism circuit, but can be connected to another user of the information, for example, a computer or a measurement indicator. In this case, the tracking servomechanism 94 and the beam deflection means symbolized by the inductor 52 can be omitted. An implementation of the circuits illustrated in FIG. 6 is described with reference to FIG. 13. The tracking signals 544, 546 received from the photodetectors of an optical pickup link are generally in a quadrature relationship, and are generally connected to inputs of differential amplifiers 548, 550, respectively. The outputs of the differential amplifiers 548, 550 represent the respective differences between their input signals 548, 550 and a displacement voltage which is produced by a voltage divider 552. The outputs of the differential amplifiers 548, 550 are inputs of multipliers 554 and 556, respectively. A function generator 558 produces an output 560 of cosine function and a sine function output 562, which are respectively the second inputs of multipliers 554, 556. An addition amplifier 564 receives the outputs of multipliers 554, 556 and generates a tracking signal 566. The tracking signal 566 is coupled back to the pickup path or optical jack of a connector 568 for insertion in the servomechanism tracking cycle. The tracking signal 566 is also coupled to a 570 potentiometer, which adjusts the local feedback loop gain. From the potentiometer 570, the tracking signal 566 is connected to a compensation circuit 572, the purpose of which is to provide phase and gain compensation in order to maintain cycle stability. The generator function 558 receives a first input 574 from the compensation circuit 572, and a second input 576 grounded. Figure 14 illustrates the function of the generator 558 in greater detail. An analog-to-digital converter 580, preferably an AD779KN, receives the inputs 574, 576 (FIG. 13) and supplies two structurally identical units, generally with the reference number 585, 595. The unit 585 generates a sine function, and unit 595 generates a cosine function. For purposes of brevity, only unit 585 will be described. Outputs 583 of analog-to-digital sharer 580 are connected to address lines 587 of a programmable memory 582 that can be erased. In this embodiment, the analog-to-digital converter 580 has a bit resolution higher than that required, and therefore the last significant bit position 586 is earthed. The outputs 583 in this way provide a vector in the programmable memory 582 that can be erased, and a corresponding sine value goes out over the data lines 588. The sine value represented by the signal on lines 588 is then converted to an analog signal in a digital-to-analog converter 590, which may be an AD767KN. The four least significant positions 592 of the digital-to-analog converter 590 are grounded, as this is the higher resolution than required. The analog output 593 is coupled to a filter circuit 594, the purpose of which is to attenuate the signal in order to eliminate the creation of an alternate name. The unit 595 differs from the unit 585 only in that a different data set is stored in its programmable memory 586 that can be erased, in order to generate a cosine function. Preferably, the data is programmed such that when a zero voltage is input to the units 585, 595, the analog to digital converter 580, the outputs 597, 598 have voltages of equal magnitude, preferably 0.7 volts. When programming the programmable memories 582, 597 that can be deleted, it is necessary to compensate the fact that the analog-to-digital converter 580 generates two complementary signals which are not sequential or linear when observed by programmable memories 582, 597, which they can be deleted. Therefore, it is necessary to adjust the data in the memories in order to generate true sine and cosine functions. The computer programs listed in Listing 1 and 2 can be executed to produce suitable data for programming the 582, 597, programmable memories that can be deleted. The conventional synchronization signals required for the function of the integrated circuits in Fig. 14 are provided by the synchronization block 600, which is illustrated in greater detail in Fig. 15. A crystal oscillator 602 operates at 24 mHZ and is coupled to a 604 counter, which can be a 74HC4060J. Synchronization signals developed by block 600 include an integrated circuit selection signal 606 or chip, integrated circuit trigger signal 608, output trigger signal 610 and a conversion trigger signal 612.

LISTING 1 / + + '| All intellectual property rights reserved by DiscoVision Associates 3/08/1996 | '| Program written by Ludwig Ceshkovsky. '| This program generates sine and cosine data for an EEPROM with | '| Input values in the 2's complement format. The output data is tabulated sequentially by the addresses of the EEPROM with the output format using binary deviation for bipolar output. | DECLARE SUB SaveData (n AS ENTIRE) DIM SHARED n AS INTEGER 'total number of memory allocations DIM SHARED C! 'total number of DIM SHARED Cstep cycles! 'value of each stage DIM SHARED Degree! DIM SHARED PROM% 'the word width of the output prom DIM SHARED chksum AS LONG' chksum for binary data file CONST sine = 1, cose = 2 CONST Pl = 3.141592654 # Degree! = PI / 180 Scales to a degree of radiance 'user of selectable parameters Cy! = 32 PROM% = 8 '8 bits of prom width PromSize% = 13' Number of address lines 13 for a 8K PROM > end n = 2 PromSize% 'total number of address positions ByScale% = (2 A PR0M%) / 2 SizeScale = n / 2' calculation offset for bipolar output Cstep! = ((Cy! * 360) / n) * Degree! 'cycles by offset stage direction! = Degree! * 45 'with zero volts in sine processing = cosine DIM SHARED PR0M% (n + 1,2) CLS Range = INT (n / 2) chksum = 0' data file for PROM PRINT programmer n, Range , Cstep !, Degree !, Cy! , ByScale% 'PRINTING test parameters OPEN "PROM01.dat" FOR OUTPUT AS # 2 'PRINT # 2, "EEPROM data"; DATE $, - TIME $; "Review" PRINT # 2, CHR $ (2); "$ A0000,"; 'for the next cycle it is not necessary to divide to order the address' the addresses are coded in two complements and the output data are 'coded by binary deviation because the output AD779 A / D is two complements' and the AD767 D / A is binary deviation. There is no binary deviation but it gives exit to deviation. K = -1 FOR¡% = 1 - Range TO Range 'low and high order direction combined K = K + 1' 1.72 is a fine adjustment to make the sine and cosine equal Asine% = ByScale% + SIN (offset ! + ((¡% - i) * Cstep)) * (ByScale% - 1) Acosine% = ByScale% + COS (offset! + ((% - 1) * Cstep)) * (ByScale% - l) 'calculate the address mode of two add-ons for the PROM IF ¡% < 0 THEN addr = ABS (%) + SizeScale ELSE addr = (%) PR0M% (K, sine) = Asine%: PROM% (K, cose) = Acosine% 'store values' PRINT HEX $ (addr), HEX $ (Asine%), HEX $ (Acosine%) chksum = chksum + Asine%' PRINT # 2, HEX $ (addr), HEX $ (Asine%) IF (K MOD 128) = 0 THEN PRINT # 2, IF Asine% < 16 THEN PRINT # 2, HEX $ (0); PRINT # 2, HEX $ (Asine%) ""; NEXT% PRINT K; "= TOTAL MEMORY LOCATIONS" PRINT # 2 PRINT # 2, CHR $ (3); "$ S"; HEX $ (chksum); "," PRINT # 2 CLOSE # 2 'test file for vissim OPEN "PROM01.TXT" FOR OUTPUT AS # 2' PRINT # 2, "EEPROM data"; DATE $; TIME $; "review" PRINT # 2, FOR% = 0 TO K PRINT%, PROM% (%, sine), PROM% (%, sew) PRINT # 2,%, PROM% (%, sine ), PROM% (%, sew) NEXT% CLOSE # 2 END: Save Data (n) SUB SaveData (n AS INTEGER) DEFINT AZ 'Save data:' Save the PROM data in a PROM01.dat file " of data.

OPEN "PROM01.dat" FOR OUTPUT AS # 2 PRINT # 2, "EEPROM data"; date; "Review" FOR a = 1 TO n 'PRINT # 2, account (a). Title NEXT to CLOSE # 2 END SUB LIST 2 '+ +' I All intellectual property rights reserved by DiscoVision Associates 3/08/1996 | '| Program written by Ludwig Ceshkovsky. '| This program generates sine and cosine data for an EEPROM with | '| Input values in the 2's complement format. The output data is tabulated sequentially by the addresses of the EEPROM with the output format using binary deviation for bipolar output. | 'I EXIT COSENO I DECLARE SUB SaveData (n AS ENTIRE) DIM SHARED n AS INTEGER 'total number of memory allocations DIM SHARED Cy! 'total number of DIM SHARED Cstep cycles! 'value of each stage DIM SHARED Degree! DIM SHARED PROM% 'the word width of the output prom DIM SHARED chksum AS LONG' chksum for binary data file CONST sine = l, cose- = 2 CONST Pl = 3.141592654 # Degree! = PI / 180 Scales to a degree of radiance 'user of selectable parameters Cy! = 32 PROM% = 8 '8 bits of prom width PromSize% = 13' Number of address lines 13 for an 8K PROM end n = 2 A PromSize% 'total number of address positions ByScale% = (2 * PROM %) / 2 SizeScale = n / 2 'calculation offset for bipolar output Cstep! = ((Cy! * 360) / n) * Degree! 'cycles by offset stage direction! = Degree! * 45 'with zero volts in sine processing = cosine DIM SHARED PROM% (n + 1,2) CLS Range = INT (n / 2) chksum = 0' data file for PROM PRINT programmer n, Range , Cstep !, Degree !, Cy !, ByScale% 'PRINTING test parameters OPEN "PROM01.dat" FOR .OUTPUT AS # 2 'PRINT # 2, "EEPROM data"; DATE $; TIME $; "Review" PRINT # 2, CHR $ (2); "$ A0000,"; 'for the next cycle it is not necessary to divide to order the address' the addresses are coded in two complements and the output data are 'encoded by binary deviation because the output AD779 A / D is two complements' and the AD767 D / A is binary deviation. There is no binary deviation but it gives exit to deviation. K = -1 F0R¡% = 1 - Range TO Range 'combined low and high order direction K = K + 1' 1.72 is a fine adjustment to make the sine and cosine equal Asine% = ByScale% + SIN (offset ! + ((¡% - i) * Cstep)) * (ByScale% - 1) Acosine% - = ByScale% + COS (offset! + ((% - 1) * Cstep)) * (ByScale% - 1) 'calculate the address mode of two add-ons for the PROM IF ¡% < 0 THEN addr = ABS (%) + SizeScale ELSE addr = (%) PROM% (K, sine) = Asine%: PROM% (K, cose) = Acosine% 'store values' PRINT HEX $ (addr), HEX $ (Asine%), HEX $ (Acosine%) chksum = chksum + Acosine% 'PRINT # 2, HEX $ (addr), HEX $ (Acosine%) IF (K MOD 128) = 0 THEN PRINT # 2, IF Acosine% < 16 THEN PRINT # 2, HEX $ (0); PRINT # 2, HEX $ (Asine%); ""; NEXT% PRINT K; "= TOTAL MEMORY LOCATIONS" PRINT # 2 PRINT # 2, CHR $ (3); "$ S"; HEX $ (chksum); "," PRINT # 2 CLOSE # 2 > test file for vissim OPEN "PROM01.TXT" FOR OUTPUT AS # 2 'PRINT # 2, "EEPROM data"; DATE $, - TIME $, - "revision" PRINT # 2, FOR% = 0 TO K PRINT%, PROM% (%, sine), PROM% (%, sew) PRINT # 2,% , PROM% (%, sine), PROM% (%, sew) NEXT% CLOSE # 2 END: Save Data (n) SUB SaveData (n AS INTEGER) DEFINT AZ 'Save data:' Save PROM data in a PROM01.dat file "OPEN data file" PROM01.dat "FOR OUTPUT AS # 2 PRINT # 2," EEPROM data "; date, -" Review "FOR a = 1 TO n 'PRINT # 2, account (a) Title NEXT to CLOSE # 2 END SUB Although this invention has been explained with reference to the structure described herein, it is not restricted to the details that are established, and this application is considered to cover any modification and change that is presented within the scope of the following claims: It is noted that in relation to this date, the best method known by the applicant to implement the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (14)

1. CLAIMS i. . An apparatus for detecting an object using a beam of radiant energy, comprising: a source for directing the beam of radiant energy to an object, - a beam detector having first and second outputs responsive to a beam position relative to the beam. object, - a circuit coupled to the outputs of the detector to produce an error signal representing a displacement of the beam from a predetermined position, in which the error signal has a periodic characteristic in relation to the displacement, - the apparatus is characterized in that has: a local feedback loop that is coupled to the outputs of the detector, the cycle comprises: a first generator of periodic function sensitive to the. error signal, - and a second periodic function generator responsive to the error signal, the second periodic function generator has an output that differs from an output of the first periodic function generator by a phase angle, - a first multiplier for multiplying the output of the detector by the output of the first periodic function generator; and a second multiplier for multiplying the second output of the detector by the output of the second periodic function generator; wherein the outputs of the first and second multipliers are provided as circuit inputs.
2. 2. The apparatus according to claim 1, characterized in that the periodic characteristic is substantially sinusoidal and the first periodic function generator and the second periodic function generator are sine generators.
3. 3. The apparatus according to claim 1, characterized in that the first and second output of the detector have an approximate mutual quadrature relation with respect to the displacement of the beam and the phase angle is about 90 °.
4. 4. The apparatus according to claim 1, characterized in that the first and second detection signals have an approximate mutual quadrature relation with respect to the displacement of the beam.
5. 5. The apparatus according to claim 1, characterized in that the detector comprises an interferometer.
6. 6. An apparatus for controlling a beam of radiant energy, comprising: a detector of the beam having first and second outputs sensitive to the position of the beam, - a circuit coupled to the outputs of the detector to produce an error signal representing a displacement of the beam from a predetermined position, in which the error signal has a periodic characteristic in relation to the displacement, - a servomechanism sensitive to the error signal to reset the beam displaced to a predetermined position; the apparatus is characterized in that it has: a local feedback loop that is coupled to the outputs of the detector, the cycle comprises: a first periodic function generator responsive to the error signal; and a second periodic function generator responsive to the error signal, the second periodic function generator has an output that differs from the output of the first periodic function generator by a phase angle, - a first multiplier to multiply the first output of the detector by the output of the first periodic function generator; and a second multiplier for multiplying the second output of the detector by the output of the second periodic function generator, - in which the outputs of the first and second multipliers are provided as circuit inputs.
7. 7. The apparatus according to claim 6, characterized in that the detector comprises an interferometer.
8. 8. A method for controlling a beam of radiant energy, the method is characterized in that it comprises the steps of: generating a first and second detection signals sensitive to the position of the beam; producing an error signal representing the displacement of the beam from a predetermined position, in which the error signal has a periodic characteristic in relation to the displacement; reset the beam moved to the predetermined position in response to the error signal; and generating a first periodic signal sensitive to the error signal, and generating a second periodic signal sensitive to the error signal, the second periodic signal differs from the first periodic signal by a phase angle; wherein the step of producing an error signal is carried out by the steps of: multiplying the first detection signal by the first periodic signal to provide a first product signal; multiplying the second detection signal by the second periodic signal to provide a second product signal, and determining a difference between the first product signal and the second product signal.
9. 9. The method according to claim 8, characterized in that the first second detection signals and the first second periodic signals are substantially sinusoidal.
10. 10. A tracking control apparatus for an optical disk system, comprising: a source for directing a beam of radiant energy to a selected track of a plurality of information tracks of an optical disk, - means for imparting relative rotational motion between the beam and the disk around an axis of rotation; a beam addressing means for moving the beam in a generally radial direction relative to the disk to follow the selected information track; a radiant energy sensitive detector that returns from the selected information track and has a first output signal and a second output signal, wherein the first output signal differs in phase from the second output signal according to the displacement of the beam from the selected track, - the apparatus is characterized in that it has: a first multiplier having electrically a first input coupled to the first output signal of the detector; a second multiplier having electrically a first input coupled to the second output signal of the detector; a difference adding amplifier having a first input coupled to an output of the first multiplier and a second input coupled to an output of the second multiplier to generate an error signal, - a first periodic function generator having an input coupled to an output of the difference adding amplifier and an output coupled to a second input of the first multiplier; a second periodic function generator having an input coupled to an output of the amplifier-difference amplifier and an output coupled to the second input of the second multiplier, and a servo-sensitive servo to the output of the difference-adding amplifier to operate the beam direction.
11. 11. The apparatus according to claim 10, characterized in that it further comprises: a cycle gain amplifier coupled to the output of the difference adding amplifier that generates an amplified error signal, - and a feedback loop compensation circuit coupled to the amplifier of cycle gain that provides the phase gain compensation for the amplified error signal.
12. 12. The apparatus according to claim 11, characterized in that it also comprises a displacer of. phase coupled to the cycle compensation circuit and coupled to one of the first periodic function generator and the second periodic function generator, wherein the phase shifter provides a predetermined voltage shift to the error signal.
13. 13. The apparatus according to claim 12, characterized in that the first periodic function generator and the second periodic function generator are sine generators.
14. 14. The apparatus according to claim 10, characterized in that the detector comprises an interferometer.