CA1072673A - Apparatus for reading a record carrier - Google Patents
Apparatus for reading a record carrierInfo
- Publication number
- CA1072673A CA1072673A CA263,410A CA263410A CA1072673A CA 1072673 A CA1072673 A CA 1072673A CA 263410 A CA263410 A CA 263410A CA 1072673 A CA1072673 A CA 1072673A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- pulse
- burst
- multivibrator
- time
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/76—Television signal recording
- H04N5/91—Television signal processing therefor
- H04N5/93—Regeneration of the television signal or of selected parts thereof
- H04N5/95—Time-base error compensation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/76—Television signal recording
- H04N5/7605—Television signal recording on discs or drums
Abstract
ABSTRACT:
Apparatus for reading a record carrier on which a television signal is recorded. In order to ensure an accurate time error measurement for a time error correction device, use is made of a burst sig-nal which is locked to the horizontal synchronizing pulses. Said burst signal may be constituted by the colour burst signal or an additional burst signal which is superimposed on the horizontal synchroniz-ing pulse. In order to obtain a pilot signal for the time error measurement a keying signal is generated with the aid of a generator which is controlled by the horizontal synchronizing pulses, the beginning of said keying signal situated within the time interval of the burst signal. The first zero passage of the burst signal which appears after the beginning of said keying signal is employed as pilot signal for the time error measurement. In order to increase the reliability of the system an automatic correction system is provided which ensures that the beginning of the keying signal lies halfway between two conse-cutive zero passages of the burst signal.
Apparatus for reading a record carrier on which a television signal is recorded. In order to ensure an accurate time error measurement for a time error correction device, use is made of a burst sig-nal which is locked to the horizontal synchronizing pulses. Said burst signal may be constituted by the colour burst signal or an additional burst signal which is superimposed on the horizontal synchroniz-ing pulse. In order to obtain a pilot signal for the time error measurement a keying signal is generated with the aid of a generator which is controlled by the horizontal synchronizing pulses, the beginning of said keying signal situated within the time interval of the burst signal. The first zero passage of the burst signal which appears after the beginning of said keying signal is employed as pilot signal for the time error measurement. In order to increase the reliability of the system an automatic correction system is provided which ensures that the beginning of the keying signal lies halfway between two conse-cutive zero passages of the burst signal.
Description
. PIIN 820iC
RJ
~t~r~ ~7~9-76 "Apparatus for reading a record carrier~'.
The invention rolates to an apparatus for reading a record carricr on which a television sig-nal is reoorded, which signal comprises horizontal I . . syn~h~onizing pulses and burst signals which are ¦ 5 . coupled to these horizontal synchronizing pulses, ¦ which burst signals`consist of a number o~ periods o~ a~carrier wave ~ith a frequency which is an in-; tegral multiple of half the line frequency, which ~ - read apparat~ls is provided ~ith a time error cor-' rection device for correcting time errors in the . . read-out television signal and a time error detec-. ~ ~ tor for detecting said time errors and supplying a .. corresponding control signal to the time error cor-.
. rection device 9 whioh time error detector comprises a kéying signal generator which is triggered by the ¦ . . horizontal synchronizing pulses, whlch generator supplies a keying signal which is delayed by a first . time inter~al relativ0 to said horizontal synchro-- .
nizing pulse, said first time interval being such that the beginning of the keying signal each time : lies within the time interval occupied by the burst : ~ :
signal, and furthermore a zero passage detector for .
detecting:the first zero passage of the burst sig-nal which appears a~ter the be~inning of said keyi.ng
RJ
~t~r~ ~7~9-76 "Apparatus for reading a record carrier~'.
The invention rolates to an apparatus for reading a record carricr on which a television sig-nal is reoorded, which signal comprises horizontal I . . syn~h~onizing pulses and burst signals which are ¦ 5 . coupled to these horizontal synchronizing pulses, ¦ which burst signals`consist of a number o~ periods o~ a~carrier wave ~ith a frequency which is an in-; tegral multiple of half the line frequency, which ~ - read apparat~ls is provided ~ith a time error cor-' rection device for correcting time errors in the . . read-out television signal and a time error detec-. ~ ~ tor for detecting said time errors and supplying a .. corresponding control signal to the time error cor-.
. rection device 9 whioh time error detector comprises a kéying signal generator which is triggered by the ¦ . . horizontal synchronizing pulses, whlch generator supplies a keying signal which is delayed by a first . time inter~al relativ0 to said horizontal synchro-- .
nizing pulse, said first time interval being such that the beginning of the keying signal each time : lies within the time interval occupied by the burst : ~ :
signal, and furthermore a zero passage detector for .
detecting:the first zero passage of the burst sig-nal which appears a~ter the be~inning of said keyi.ng
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27.9.76 2~3 signal.
In this respect it is to be noted that a re¢ord carrier generally contains sùch a television signaL in coded form, i.e. that this television sig-S nal is coded iIl a specific manner be~cre it is re-cordcd. In accordance with a frequently used coding the complete television signal) for example a standard PAL or NTSC colour television signal, is frequency modulated on a carrier wave. In other coding systems the luminance and chrominance signals are added to separate carrier ~aves. The coding to which the te].e-vision signal has been subjected during recording is irrelevant for the present invention, provided that this television signal still exhibits the specified composition with-horizontal synchronizing pulses and associated burst sig~als after the complementary de~
codingO
Signals which are read from a record carrier generally sxhibit time errors. When reading record 3 .20 carriers in the form of a tape, these time errors are inter alia caused by variations in the trans-.. . .
port speed and stre~ch of such record carriers. When reading disc-shaped record carriers these time errors may bs caused partly by variations in the transport speed, (in this case the speed of rotation) of the record carrier and partly by eccentricity of the ; drive point relative to the centre of the record carrier.
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27.9~76 These time errors are very disturbing when reproducing a television signal which is recorded on a record carrier in particular in -the case of a colour tele~ision signal in which two colour ColJlpollentS are quadrature-modulated on one and the same colour car-rier wave~ In such colour television systems said time errors produce very annoying colour hue variations~
which are not acceptable.
Apparatus for reading such record carriers therefore usually include a tim~ error correc$ion sys-tem, with which these time errors can be corrected as far as possible. In such read apparatus both electro-mechanical ser~o systems and fully electronic systems may be used as time error correction systems~ For ~, 15 example in apparatus for reading record carriers in the form of a tape it ls common practice to c~ntrol both the transport speed of the record carrier and the speed with which the read head moves along the record carrier in accordance with the time errors measured. In the case of apparatus for reading a disc-shaped record carrier the same is effected with respect to the speed ~ rotation of the disc-shaped record carrier. Moreover, such read apparatus ge-nerally include an addi~ional correction system in the scanning~unit, In the case of a mechanical scanning system this additional correction system ~or example controls the po~ition of the scanning ' - ~
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head in the longitudinal direction of the track on the record carrier. In the case o~ an optical reacl system, the in~ormation on the record carrior is read with the aid of a beam of radiation and the position of the scanning spot produced on the record carrier by said beam is controlled in the longitudinal direc-tion o~ the track. Electronic time error correction sys-. tems may emplo~ variable delay networks such as bucket brigades, CCD~s (charge-coupled devices) and the like.
In all these time error correction devices it is of great importance that the time errors con-tained in the read-out television signal can be measured with high ac¢uracyO In addition, it is : 15 desirable that suoh a time error correction device ., .
-: has a fairly wide control range, for which purpose the time errors should be measured over a substan-~ tially wide range~
- In "I.E.E.E. Transactions on~Broadcasting", Vol. BC-17, No. 1, March 1971, page 35, a time error -: :
detector device for an NTSC colour television signal is desoribed which meets these two requirements. In this device use is made of the colour burst signal . ; on the backporch of the her~R~Dtal synchronizing ~:~ ; 25 pulse in this NTSC colour televisiol1 signal. This :
- colour burst signal consists o~ a number of periods of a c~arrler wave of a frequency whlch is an odd ,;; ~:
: - 5 , , P~IN 8201C
27.9.7 :~t~2~3 integral multiple of half the line frequency, said burst signal having a fixed posi-tion relative to the correspondlng horizontal svnchroniz:ing pulse. A key-ing signal generator which is triggcred by this ho~
rizontal synchroni~ing puls0 produces a koying sig~
nal, which lies within the time interval occupiecl by the co:Lour burst signal. By detecting the first colour burst zero passage appearing after the begin-ning of this keying signal a pilot signal of line frequency is obtained from which the desired control signal for the time error correction device is deriv-ed by comparison with a reference signal of line fre-quency. As a zero passage of the colour burst signal can be detected in a very accurate ~anner, the time error meaaurement thus becomes highly accurate.
Moreovar, ~inoe in fact use is made of a pilot tone of line frequency~ the time error measuring range, - and thus the range of the time error correction, cor-responds to one line period of the television signal.
For the time error detection described above it is essential that the beginning of the keying sig-nal within the time interval of the burst signal is well defined, in order that always the same zero passage of said burst signal ultimately functions as the pilot signal. However, the relative positions of the horizontal synchronizing puls0, specifically its leading 0dge, and said burst signal ar0 not ac- ;
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curately defirled. As a resul-t of this, the beginning of the keying signal, which is derived from this ho-rizontal synchronizing pulse, is neither accurately defined. This may lead to an erroneous time error n~easurelnent in that, owing to -the change of the zero passage of the burs-t si~nal which acts as a pilot signal, a time error is indicated without the ac-tual occurrence of a time error in the read-out signal.
It is an object of the invention to avoid this problem and the apparatus according to the in- t vention is therefore characterized in that the time error detector comprises a measuring circuit for measuring the time interval between the beginning of this keying signal and the next zero passage of the burst signal which is detec-ted and supplying a correspoAding correction signal, and that the keying s signal generator is adapted to supply a keying sig- !
nal which relative to the horizontal synchronizing 3 pulse has a delay equal to a first time interval which is variable depending on the correc-tion sig-nal.
The step in accordance with the lnvention ensures that the beginning of the keying signal is always situated halfway between two consecutive zero passages of the burst signal regardless of~
changes in the posi-tion of the horizoAtal synchro-', ~ jt~ ~ : 27.9.76 nizing pulse relati~e to the burst signal r thus po-sitively ènsuring that always the same zero passage of said burst signal~functions as pilot signal for the time error d0tection.
, The invention is by no means limited to the use of the colour burst signal as s-tated here~
inbefore with respect to the NTSC colour television signal. As an alternative an additional burst~slg-nal may be added to the television ~ignal to be re-corded in an appropriata time inter~al during each line period. An example of this is the insertion of a burst signal during the time interval of the ho-rizontal synchronizing pulse 9 resulting in a burst signal which i5 superimposed on said horizontal ~, - - 15 synchronizing pulse, which possibility is describ-ed in "Consumer Electronics~', 5-1-76, pages 54 and further. The use of such an additional burst signal , is of particular importance when utilizing ~ PAL-standard colour television signal, because in this case the colour burst signal itself cannot be used .
~ for the, describ0d time error detection owing to .
the standard coupling with the llne frequency.
, Although~the invention is by no means limited to such a system, the~invention will be described hereinafter on the basis of an optical , read system ~or disc-shaped record carriers. In the drawing: ~ ~
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' 27.9 .76 Zj~;t~;3 Fig. 1 shows such an optical read system, ~ig. 2 schema-tically shows t~e known time error measuring system, and Fig. 3 shows the signals associated with this system.
Fig. 4 shows the time error measuring system in accordance with the invention, and Fig. 5 sho~s the associated signalsO
Fig. 6 shows a practical embodiment of the ~eying signal generator utilized in the apparatus - in accordanoe with the invention.
Fig. 7 is an extension of the measuring system, and Fig. 8 represents an additional burst sig-nal on the line synchronizing pulse.
The read apparatus shown in Fig. 1 is suit-able-for reading a disc-shaped rccord carrier 1, on whose upper surface tracks are formed (e.g. as turns of a spiral) in which the information is recorded a relief pattern. This track form and method of cod-ing on the record carrier is irrelevant for the principle of the invention~ The disc-shaped record carrier 1 is rotated in a direction V1 with the aid of a motor 2 with a disc-supporting spindle 3, which proJects through a central opening 4 of the record ca~rier 1~
~he optical system for reading the record _ 9 27,9,76 6'~
carrier 1 is accommodated in a housing 5. This optical system first o~ all cosnprises a radiation source 6.
This radiaticn source ~mits a radiat:ion bearn a1 which via a semi-transparent mirrcr 7 impinges on a mirror 8 and is reflected by this mirror 8 as a radiation beam a2. This radiation beam a2 is reflected as a radiation beam a3 by a mirror 9, which beam is fo-cussed by a lens 10 into the scanning spot P on the upper surface of the record carrier 1. This upper surface of the record carrier 1 is reflecting, so that a radiation beam al~ (which is modulated hy the information) is reflected and via the lens 10 impinges on the mirror 9 is reflected as a radiation beam a5 and is then reflected by the mirror 8 as a radiation beam a6. This radiation beam a6 impinges on the semi-~ transparent mirror 7 so $hat a part of this radiation bcam is re~lected as a radiation beam a7 which is in-cident on a read detector 11. This schematically re-presented read detector 11 detects the information contained in the radiation beam a7 and supplies a corresponding electrical signal to an output ter-minal 12.
This signal at the output terminal 12 is applied to a decoding de~ice 18, which converts the applied television signal (which is coded in a spe-ciflc manner) into a standard televislon signal - which iB available at a terminal 19. It is obvious . , .
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that the design of this decoding device is determined by the coding of the television signal used during recording on the record carrierO If, for example, a composite system is employed,~in which the complete standard television signal (i~e. the complete combi-nation of lum.inance and chrominance signals~ is added to a carrier wave as frequency modulation, this de~
coding device employs a frequency d~modulator. The coding method is irrelevant for the principle of the invention.
In order to ensure that th~ scanning spot P
is always incident on the information track on the record oarrier, a radial tracking control system is provided with which the radial position of the scan-ning spot is controlled. This control system first of all comprises a measuring detector for measuring the radial position of the scanning spot P. For the sako of simplieity it is assumed that this measur-ing detector-is included in the read detector 11 a~d that it supplies a control signal to a terminal 13. Examples of systems with which this radia1 po-sition of the scanning spot can be measured can be found in the said United States Patent Specifica-tion No. 3,381,086, United States Patent Specification No. 3,876,84~ (PHN. 6292), and Canadian Patent Spocification No. ~57,o67 (PHN.5503). rnis control signal at the terminal 13 is applied to a drive .
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means 15 by which the mirror 8 can be pivoted in the direction V2 about the axis 14. By pivoting this mir-ror 8 the di.rection of the beam of radiation a1 is changed and thus the radial position o~ the scanning spot P. From the avera~e angular position of this mirror 8. a second control signal i5 derived for a drive means 16 by which the housing 5 can be moved in a radial direction V3.
Owing to the variations in the speed o.~ the drive motor 2 and/or eccentricity o~ the opening 4 relative to.the centre of the record carrier 1, the read-out television signal exhibits time errors, which are dis-turbing, particularly with respect to the colour reproduction. In order to correct these .15 time errors a time error correction system is includ-ed in the optical read system. This ti.me error cor-rection is achieved with the aid o~ the mirro 9 which is rotatable by means of a drive element 17 in a direction V4. By pivoting the mirror 9 in this : 20 direction the scanning spot P is moved in the longi-tudinal direction o~ the in~ormation track on the . record carrler 1, so that said time error -can be corrected.
The control signal required ~or said drive element 17 i9 obtained with the aid of a time error detector 25. The decoded television signal is applied to this time error detector. The time error detector .
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25 first of all comprises a device 20 for extracting a pilot signal suitable for time error measurement from said decoded television signal. The circuit ar-rangement of this device 20 will be described later.
The pilot signal, which has been extracted by the device 20 and whose frequoncy and phase represent the time errors, is applied to a phase compa-rator circuit 21, which also receives a reference signal from an oscillator 22. The measured phase difference between the two signals is then a measure of the time errors and is used to ~ tain the desired control signal for the drive element 17 via a control am-plifier 23. The Figure also shows a possibility o.f deriving the control signal f`or the drive motor 2 for the record carrier 1 Prom said time error de-tector 25 via a control amplifier 24. It is evident that any other pilot signal contained in the .tele- ¦
vision signal may also be used for thls purpose, because the two control s~stems need not comply with the same requirements.
The previously mentioned known form of the devicc 20 for extracting a suitable pilot signal is schematioally shown in Fig. 2, whilst Flg. 3 shows the associated signals~ In order to clarify the operation of the device of Fig. 2 reference is first of all made to Fig. 3a. Fig.~3a shows a ho-rizontal synchroni~,ing pulse S followed by the , PHN 8~01C
27.9.76 2~3 colour burst signal B in accordance with the NTSC-standard on an enlarged scal~. To simplify the draw-ing the time scale has been in-terrupted within the hori~ontal synchronizing pulse. The ~requency o~ the colour burst signal B is an odd integral mul-tiple of' hal~ the line frequency. This means that exactly one line period a~ter a specific ~ero passage of -this colour burst signal another zero passage of ' the colou~ burst signal corresponding to the next line peri.od appears. This is utilized in the de-vice of Fig. 2.
This device has been adapted to detect al-ways the same zero passage of the colour burst sig-- nal, so that a line-sequential pilat signal is ob-tained, which on the one hand results in a wide con-trol ran,ge of the time error correction device and on the other hand enables accurate time error measure-.
ments to be made. This accuracy result from the fact that the edges of the colour burst signal are very steep, thus enabling the relevant zero passage to be detected in an accurate manner, whilst moreover the disturbing influence of noise which is super-imposed on the read-out television signal can sub-stantially be reduced in a simple manner with this zero passage detection 'by previously passing t~is , - burst signal through a narrow-band ba,nd-pass fil-' ' ter.
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. PHN 82010 ~,7~3 27,9.76 In order to ensure tha-t always the same zero passage o~ the colour burst signal is detected, -tho device 22 of Fig. 2 comprises a pulse gcnerator 38, This pulse generator 38 is triggered by -the horizon-tal synchronizing pulse, specifioa:l.ly by the leading edge thereo~ 9 between -the horlzonta.l blanking level VB and the peak level VT, which synchronizing pulse is extracted from -the decoded -television signal.
For this purpose the device 20 includes a low-pass 1-0 filter 36, which is connected to the input terminal 31 and to a.sync separator 37 which is connec-ted to this low pass filter 36, which separator in known manner detects the horizontal synchronizing pulses S, for example with a threshold value detector with a threshold value VD, and supplies pulses (see Fig.
3c) which coincide with the synchronizing pulses to the keying signal generator 38. This keying sig-nal generator 38 comprises a first monostable multi-vibrator 39 which is triggered by these horizontal synchronizing pulses and in response thereto supplies pulses T(see ~ig. 3d)~ the duration of -these pulses T being selectsd so that the trailing edge of these pulses T appsars within th.e timo interval occupied . by the burst signalO This pulse T is applied to a second monostable multivi~rator 40, which is trig-gered by the trailing edge of this pulse T and in response thereto supplies a pulse W (see Fig. 3e).
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~7~3 This pulse W for example has as a pulse width of 140 nanoseconds, ~.e. a half period of the colour burst signa:L~
The output o:~ the pulse generator 38, which supplies this pulse 1~, is connected to a first input 45 of a gate circuit l~1. Ta a ~econd input l~l~ short pulses (see Fig. 3b~ are applied, which represen-t the ~ero passages of the burst signal B. For this purpose the device 20 includes a low-pass filter : 10 32 by means of which the frequency band in which the frequency of said burst signal is situated is extracted from the television signal applied to the input terminal 31. The extracted signal is amplifie~
and limited with the aid of a limiter circuit 33 in order to obtain a square wave signal and the zero passages of this square wave signal are deLected . with the aid of a de-tector 34, The detector 34 operates in an absolute manner in the case of an NTSC colour television signal, i,e, the detector 34 supplies an output pulse upon each zero passage of the burst signal, regardless of the sign of the slope, This is necessary in the case of an NTSC
colour television signal because the burst signals B and Bt in two consecutive line periods are in phase opposition (see Fig, 3a) o~ing to the fact that~the chrominance carrier ~requency is locked -to half the line frequency~
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~ 3 The gate circuit 41 (perI'orms an AND-function for the signals at its inputs ll4 and 45, which means that the output pulse of thls gate circui-t 1-~1 f;~
(see Fig. 3b) always corresponds to that pulse from the æero passage detector 34 wh:ich appears within the time interval of the pulse W from the pulse ge-nerator 38. As a resul-t, a pulse is generated line-sequentially (Fig. 3f) which can be utilized as a pilot signal for time error measurement. If desired, 10 ~ this pulse may also be applied to a monos-table multi-- ; Yibrator 42, which derives pulses with a specific pulse width therefrom, which are th0n a~ailable at the output terminal 43 and may be applied to the compara-tor circuit 21 of Fig. 1 as a pilot signal.
If the pulse width selected for the pulses supplied by the monostable multivibrator 42 is greater tllan - the pulse width of the pulses W frorn the pulse ge-~ nerator, substan-tially any pulse width may be used ; for these pulses W, because then only the first pulse from the zero passage detector 34 will re-sult in an outpu-t pulse of the multivibrator 42 during a pulse W.i In order to increase the reliability of operation of the device it is useful to include a detectQr 35 which is connec~ed to the low-pass filter 32 and which detects the presence of a colour burs-t signal. This detector conscquently ~ ~ .
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27.9.76 Y~ 3 supplies an output pulse as soon as and as long as this colour burst signal is present. This output pulse o:f the colour burst detector ls also applied to the gate circuit 1~1 (input 1~6), so 1;ha-t this gate circui-t can only supply an output pulse in the pre-sence of a colour burst signal. This additional cir-cuitry caters for the fac-t that during the vertical flyback period of the television signal a nwllber of picture lines contain no colour burst signals. Should the zero passage detector 34 supply a pulse within the pulse W, despite the absence of a colour burst signal (for example owing to the occurrence of noise) this does not give rise to an (erroneous~ pulse at the output of the gate circuit.
The effect of -this ~dditional circuitry be-comes more apparent ~len taking into consideration that in the most frequently used version o~ the com-parator circuit 21 a "hold effect" occllrs if no pul-ses are supplied by the pilot tone separator. This comparator circuit 21 generally operates with a ; sawtooth-shaped re~erence signal from the oscilla-tor 22, which signal is then sampled at instants which are defined by the pulses of the pilot tone sepàrator, This sampled value is subsequently re-tained until the next sampling oocurs. As long as the pilot tone separator 20 supplies no pulses, i.e.
during a portion of the vertical flyback period, the : , .
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last sample value is retained as a control signal for the time error correction system.
However, an erro~eous pulse from the pilot tone separator during the vertical flybacl~ perlod would control this time error correction system in a completely incorrect mannor. It is true that af-ter the occurrence of ~some picture lines having colour burs-t signals, this time error correction system will be pulled in again, but as this is ob-viously involves a delayed response, it could still give rise to disturbances in the displayed picture.
In order to minimize the time during the vertical flyback period that no measuring signal is available it is of course also possible to add additional burst signals to the television signal ; to be recorded during this vertical flyback period.
A problem associated with the prcviously described method of generating a suitable pilot - signal for time error measurements is caused by the faot that the position of the horiæon-tal synchroniz-ing pulse relative to the burst signal is not accu-- rately defined. This has various causes. First oP
' all, the accuracy with which the horizontal syn~
chronizing ~ulses are generated prior to recording of the -television signal is liniited. Furthermore, as previously stated, the accuracy with which these - horlzontal synchronizing pulses can be detected dur-- .
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27.9,76 ~Z~3 ing reproduction is limited and in this respect the susceptibility to noise plays a part. Furthermore, -the phase relation bet~een the hor:izontal synchro-nizing pulses and tlle colour burst signal is dis-turbed, since th:is b~rs-t signal has been passed through a band-pass filter.
As the keying signal 1~ is directly derived from the detected horizontal synchronizing pu]se this means that the position of this keying signal within the time interval of the burst signal is - neither accurately defined. In the ideal case the instant at which said keying signal W starts, i.e.
the position of the leading edge, ls situated exactly halfway between two consecutive zero passages of the burst signal. If this keying signal W is now shifted ; owing to the inaccuracy of the position of the hori-;
zontal synchronizing pulse, it may for example happen that the leading edge of this keying signal does no~
appear until after the desired ~ero passage of the burst signal, as is shown in Fig. 3h~ In that case the next zero passage of the burst signal is then utilized for generating the pilot signal (see Fig.
31). This change from the one zero passage to the ~: next zero passage for the generation of the pilot signal manifests itself in the tims error detection ; as a time ~rror of 140 nanoseconds, namely -the in-t0rval between these two zero passages, thus result-_ 20 2~.9.76 q;~73 ing in an incorrect time error measurernent and conse-quently in an incorrect timo error correction.
This problem is avoided owing to the step in accordance with the invention. The step in ac-cordance with the inventioIl main:Ly affects the ci.r-cuit arrangement of th~ Iseying signal generator 38.
In order to explain the step in acoordance with the invention ~ig. 4 schematically sho~s the circuit ar~
rangoment of the pulse generator 38 together with the ga-te circuit 419 which circuits form part of the device of Fig. 2.
The pulse generator 38 sho~n in Fig. 4 oom-prises a monostable niultivibrator 51 to whose input 54 the extracted horizontal synchron~zing pulses supplied by ~he sync separator 37 are applied ; ~ (FigQ 2). This monostable multivibrator 51 supplies ~a pulse T'which is applied to a set input 55 of a , : multivibrator 52, whose output is connected to the input 45 of the gate circuit 41. The pulse from the :!
. zero passage detector 34 is applied to the input 4l~
o~ the gate circuit 41 so as to be keyed out with the : aid of~said gate circuit, after which it is applied to the reset Input 56 of` the multi~i'brator 52, as the case may be after'processing by the monostable ,~ 25 multivibrator 42. Howcver, the pulse width of the : , pulse T which is supplied by the monostable multi-- vIbrator 51 iS~ not cDnstant but is ~ariable depend-`
: ~ ~ ing on a correction signal ~hich is fed to a control . iDpUt S7 o~ this monostable multivibrator 51.
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27.9.76 ~7~
The operation of the circuit will now be described with reference to Fig. 5. Fig. 5a shows a number of pulses which are supplied by the zero pas-sage detec-tor 34 and which thus represent the zero passages o~ the burst signal. Fig. 5b shows a pulse T supplied b~ the monostable multivibrator 51, whose leading edge again coincides with the leading edge of the horizontal synchronizi.ng pulse and whose trailing edge of situated within the time interval occupied by the burst signal. In the ideal situation the trailiDg edge of` this pulse T should occur at an instant t exactly halfway between two successiv~
zero passages of the burst signal. However, it is assumed that owing to the inaccuracy of the horizon-tal synchronizing pulse this trailing edge appears at an instal~t t1. This trailing edge of the pulse T triggers the multivibrator 52, so that said mul tivibrator chan~es over (~ 5c). When at the in-stant t2 a pulse Q from the zero passage detector i9 applied to the gate circuit 41 a pulse (Fig. 5d) is produced at the output of the monostable multi-vibrator 42, which pulse is applied to the reset ,~ input 56 of the multivibrator 52. Th~s pulse resets the multivibrator 52 to its original state at the instant t2, so that the output signal of this mul-.~ tivibrator.is the puise W shown in Fig. 5c.
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' - . - 22 ~ ' ' ' ' ~
. PHN 8201C
27.9.76 From the Figure it is evident that the pulse width t o~ this pulse W corresponds to the time in-terval t2-t1, so that it is a measure o~ the po~i-tion of the trailing edge of the pulse T between tho two c~ns0cutive zero passages of the burs-t signal. T.his data is utilized by the invention or automatically correcting the positi~on of the trailing edge o~ the pulse T. The pulse width t~ of -the pulse W is measur-ed with the aid of a measuring circuit 53 and convert-ed into a correction signal ~or the monostable multi-vibrator 51. In the example of Fig. 5 this correction signal will result in a reduction of the pulse wid-~h ; Or the pulse T, in such a way that the trailing edge ., . of this pulse T is moved towards thQ instant to.
. ~ 15 (Fig. 5e), which in its turn results in a pulse W
from the multivibrator 52 in accordance with Fig.
~f.
Thus it is achieved that the leading edge - of the keying signal W is always controlled towards . 20 a position halfway be-tween two consecutive zero passages of the burst signal, so that symmetrically about this position a maximum tolerance is permis-sible without giving rise to an erroneous time error-. I , ,I mea~urement. The multivibrator 52 preferably tak0s the form of a monostable which in the absence of a reset signal at the input 56 is automatically reset . ' ' ' . ' . :
~ 3 P~IN 8201C
` 27.9.76 :~'7~ 3 .' after for example 140 nanoseconds A practical embodiment of the monostable multivibrator 5I in conjunction with the measuring circuit 53 is shown in Fig. 6~ The measuring circuit 53 comprises a capacitance C2(4.7/u~) which is con-nected to a voltage source V2 and which is charged via a resistor Rl~(220 kohms). The charge of this capacitance C2, i.e. the voltage acrpss it, depends ?
: on the signal on the base of a transistor T1. The ~, base of the transistor T1 receives the output pulse W of the multlvibrator 52 and this transis.tor con-ducts for the duration o~ this pulse, so that the voltage across the capacitance C2 Is determined by `. the pulse duration of this output pulse W of the : ~ 15 multivibrator 52. The voltage across the capacltance : ~ . C2 is applied to an emitter~follower T2 and with the aid of a resistor R3 (150 kohms) it is converted in-to a control current which is appliod to the control .terminal 57 of the monostable multivibrator 51.
This monostable multivibrator 51 comprises an integrated multivibrator circùit 58 of the type SN 741e3 (Sign0tics), whose time constant, i.e.
pulse duration, is determined by the capacitance , C1(3300 pF) and the resistors R1(2.2 kohms) and : 25 R2(6.2kohms). As the control input 57 is connected : ~ to this capaci~ance C2 the charge on this capacitance- -.
. ~ .
C2 and thus the time constant depend on the correction ' , .
2l~ _ .
PHN ~201C
27.9.76 ~r7Z~73 current. By dimensioning the resistors and capacitan-ces as specified it is achieved that the pulse dura-tion of the output pulse of this rnonostable multlvi-brator circuit 58 as a ~m~tion o~ the correction current can ~ar~ minimum appro~ 140 Danoseconds, i.e. ma~imum hal~ the period of the NTSC colour .
burst signal. It is obvious that many modifications to this circuit arrangement are possible. For exam-ple, it is also possible to use a variable delay means instead of -the monostable multivibrator.
Fig. 7 shows a variant of the circuit ar-rangement of Fig. 4, corresponding elements being denoted by the same re~erence numerals. The output signal of the limiter circuit 33 in this circuit arrangement is not applied directly to the ero passage detector 34, but is applied both directly to an input 64~and via an inverting amplifier 61 to an input 63 of a two-position switch 6~ whose master contact 65 is connected to the zero passage detector 34~. This switch 62 i5 controlled by a control cir-cuit 66 whlch receives the horizontal synchronizing pulse train supplied by the sync separator 37 at an :, :
input 67. This control circuit 66 then supplies a symmetrical control signal of half the line fre-quency to the switch 62 so that this switch is changed over from line to line. Thus~ it is ensured that the colour burst signals ~ consecutive lines, 27.9.7G
~ 6~3 which are applied to the zero passage detector 34' always have the same phase with respect to each other, This means that this zero passage detector 34l no longer need be of the absolu-te type, as in tho ver sion in accordance with Fig. 4, but should merely respond to the zero passages which occur in the case of one specific sign of -the slope of the colour burst signàl. This moans that this zero passage detec~
tor 34' may then taka the form of a simple monostable multivibrator.
As pr0viously stated, the in-vention is by no means limited to optical read apparatus, but is also applicable.to read apparatus for a magnetic re-cord carrier in the form of a tape. ~Irthermore~ the circuit arran~ement of the time error.correctivn sys-tem is not limited:to the system described, In prin-cipl0, any suitable time error correc-tion system, whether electromechanical or electronic, may be used, the ultimate choice being generally determined by the ., ;
type of read system.
Furthermore, the in~en-tion is not limited to - the coding system des~ribed by way of example, in i which a complete standard NTSC colour television sig-, nal is frequency modulated on a carrier wave. The invention may for example equally be used with cod- ;
îng systems in which, during recording, the c~romi- ~
:
~ nance signal is extracted and transposed -to a lower :
: frequency band~ i.e. is record.0d as a modulation of .~ , - ' ' .
.
27~9.76 .
a separate chro~ninance carrier wa~e, whilst the lumi-nance signal lS frequcncy modulated on a carrier wave of comparativel.y high frequency. In such coding 5yg-tems the ~requency of the s~pa~ate chrominance carrier is generally arl integral multiple of half the line f`requency. During reproduction the read-out chromi-nance signal is than re-transposed to the standard frequency band by mixing it with a suitable mixing frequency, so that again a standard NTSC or PA~
colour television signal is obtained. By ensuring that the mixing frequency has the same time errors as the read-out chrominance signal, the influence of these timing errors on the ultimately obtained standard colour television signa~l is substantially : 15 reduced. By the indicated choioe of the frequency of the separate chrominance carrier it is achieved that ., as pilot tone for producing this ~ixing frequency use can slmply be made of the read-out horiz.ontal synchronizing pulse train as is for example compre-hensively described in United States Patent Speci.fi-cation 3,803,3l~7 (PHN 4978). Instead of this horizon-. ~ .
.~ ~; tal synchronizing pulse train it is then obvious .
that use can also be made of a æero passage of the colour burst signal with the aid of ~ device in ac-J
cordance with the present invention. In that case it ; ~ is also possible to~use.the colour burst signal pre-~ ' ~
..
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27 . 9 , 7G
'Z6~;~
sent in the colour signal, or an additional burst si.g-nal on the backporch of -the ho:rizonta:L syncllronizing pulses, which has been added -to the luminance signal during recording.
Furthermore it is not necessary to separate the pilot tone from the;...complete decoded television signal (output of decoder 18). Dependent on the cod-ing system this pilot tone could be -sepa~ateds~1ome-where wi'thin the decoding process.
It is to be noted that although the invention will primarily be used to advantage ~or.reading out a colour televislon signal, this invention may also be ~ used for reading out a black-and-white television - signal. For this purpose, it will only be necessary to add burst signals on tha backporch of the horizon-tal s~nohronizing pulses during recording.
Fina].ly, the possibility will be described of adding an additional burst signal to the televi~
sion signal during recording, which burst signal may be utiliz0d for accurately measuring the time : errors during r~production, This possibility is represented in Fig. 8. This Flgure again sho~ys a horizontal synchronizing pulse S of a television slgDal with a horizontal blanking level:VB and a peak level VT. However, prior to recordingl a burst signal E has been superimposed on this hori~
zontal synchronizlng pulse S, i.e. on the peak level -. ' ~ .' , ~ 28 '.~ ' . ' ' ' 27.9.7G
~ 7~
VT thereof. This burst signal L has a frequency which is an integral multiple of half the line frequency and preferably an integral~mllltiple of the whole line frequency.
During reproduction of the recorded tele-vision signal this additional burst signal is ex-tract~
ed, after which in a similar way as described herein-before with respect to the NTSC colour burst signal the positionof a specific zero passage of this addi~
tional burst signal can be detected during each line period and can serve for measuring time errors. ,~
The use of this additional burst signal is of special importance when recording and reproducing a colour television signal which complies with the PAL standard. In this case the colour burst signal cannot simply be used in the described time error measuring system because the frequency ~f said PAL
colour burst signal lS an odd multiple of 1/l~ fH and moreover exhibits a 25-Hz offset.
If furthermore an additional burst signal with a frequency equal to a multiple of the line frequency is used, a~non-absolute zero passage detec-tor may be used for detecting the zero passages, i.e.
a detector which detects only the zero passages which correspond either the positive-going or the negative-going edges. Thus, the time interval within which the beginning of the keying signal should occur is - ~ .
~ 29 27.9.76 ~ 3 doubled compared with the use of the NTSC colour burst signal, because this now corresponds to a f`ull period of' the burst signal. Finally, the use Or this additional burst signal superimposed on the horizontal synchroniz-ing pulse has the advantage -that -the first -time i.nter-val, i.e. the time between the leading edge of' the horizontal synchronizing pulse and the koying signal is substantially shorter than when the colour burst signal is ùsed, This shorter time interval can be realized more accurately with the aid o~ multivibrator .
cir~uits, which adds to ths reliabiLity of ths systsm.
,~
.
. ..
~, .
' 1~ ., . ~_ 30 _ .
.
PllN 8201C
27.9.76 2~3 signal.
In this respect it is to be noted that a re¢ord carrier generally contains sùch a television signaL in coded form, i.e. that this television sig-S nal is coded iIl a specific manner be~cre it is re-cordcd. In accordance with a frequently used coding the complete television signal) for example a standard PAL or NTSC colour television signal, is frequency modulated on a carrier wave. In other coding systems the luminance and chrominance signals are added to separate carrier ~aves. The coding to which the te].e-vision signal has been subjected during recording is irrelevant for the present invention, provided that this television signal still exhibits the specified composition with-horizontal synchronizing pulses and associated burst sig~als after the complementary de~
codingO
Signals which are read from a record carrier generally sxhibit time errors. When reading record 3 .20 carriers in the form of a tape, these time errors are inter alia caused by variations in the trans-.. . .
port speed and stre~ch of such record carriers. When reading disc-shaped record carriers these time errors may bs caused partly by variations in the transport speed, (in this case the speed of rotation) of the record carrier and partly by eccentricity of the ; drive point relative to the centre of the record carrier.
, .
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Pl-IN 8201C
27.9~76 These time errors are very disturbing when reproducing a television signal which is recorded on a record carrier in particular in -the case of a colour tele~ision signal in which two colour ColJlpollentS are quadrature-modulated on one and the same colour car-rier wave~ In such colour television systems said time errors produce very annoying colour hue variations~
which are not acceptable.
Apparatus for reading such record carriers therefore usually include a tim~ error correc$ion sys-tem, with which these time errors can be corrected as far as possible. In such read apparatus both electro-mechanical ser~o systems and fully electronic systems may be used as time error correction systems~ For ~, 15 example in apparatus for reading record carriers in the form of a tape it ls common practice to c~ntrol both the transport speed of the record carrier and the speed with which the read head moves along the record carrier in accordance with the time errors measured. In the case of apparatus for reading a disc-shaped record carrier the same is effected with respect to the speed ~ rotation of the disc-shaped record carrier. Moreover, such read apparatus ge-nerally include an addi~ional correction system in the scanning~unit, In the case of a mechanical scanning system this additional correction system ~or example controls the po~ition of the scanning ' - ~
P}IN 8201C
27.9.76 Zfi~
head in the longitudinal direction of the track on the record carrier. In the case o~ an optical reacl system, the in~ormation on the record carrior is read with the aid of a beam of radiation and the position of the scanning spot produced on the record carrier by said beam is controlled in the longitudinal direc-tion o~ the track. Electronic time error correction sys-. tems may emplo~ variable delay networks such as bucket brigades, CCD~s (charge-coupled devices) and the like.
In all these time error correction devices it is of great importance that the time errors con-tained in the read-out television signal can be measured with high ac¢uracyO In addition, it is : 15 desirable that suoh a time error correction device ., .
-: has a fairly wide control range, for which purpose the time errors should be measured over a substan-~ tially wide range~
- In "I.E.E.E. Transactions on~Broadcasting", Vol. BC-17, No. 1, March 1971, page 35, a time error -: :
detector device for an NTSC colour television signal is desoribed which meets these two requirements. In this device use is made of the colour burst signal . ; on the backporch of the her~R~Dtal synchronizing ~:~ ; 25 pulse in this NTSC colour televisiol1 signal. This :
- colour burst signal consists o~ a number of periods of a c~arrler wave of a frequency whlch is an odd ,;; ~:
: - 5 , , P~IN 8201C
27.9.7 :~t~2~3 integral multiple of half the line frequency, said burst signal having a fixed posi-tion relative to the correspondlng horizontal svnchroniz:ing pulse. A key-ing signal generator which is triggcred by this ho~
rizontal synchroni~ing puls0 produces a koying sig~
nal, which lies within the time interval occupiecl by the co:Lour burst signal. By detecting the first colour burst zero passage appearing after the begin-ning of this keying signal a pilot signal of line frequency is obtained from which the desired control signal for the time error correction device is deriv-ed by comparison with a reference signal of line fre-quency. As a zero passage of the colour burst signal can be detected in a very accurate ~anner, the time error meaaurement thus becomes highly accurate.
Moreovar, ~inoe in fact use is made of a pilot tone of line frequency~ the time error measuring range, - and thus the range of the time error correction, cor-responds to one line period of the television signal.
For the time error detection described above it is essential that the beginning of the keying sig-nal within the time interval of the burst signal is well defined, in order that always the same zero passage of said burst signal ultimately functions as the pilot signal. However, the relative positions of the horizontal synchronizing puls0, specifically its leading 0dge, and said burst signal ar0 not ac- ;
., ~, ~ .
~ 6 .
.
2'7,9.76 Z~
curately defirled. As a resul-t of this, the beginning of the keying signal, which is derived from this ho-rizontal synchronizing pulse, is neither accurately defined. This may lead to an erroneous time error n~easurelnent in that, owing to -the change of the zero passage of the burs-t si~nal which acts as a pilot signal, a time error is indicated without the ac-tual occurrence of a time error in the read-out signal.
It is an object of the invention to avoid this problem and the apparatus according to the in- t vention is therefore characterized in that the time error detector comprises a measuring circuit for measuring the time interval between the beginning of this keying signal and the next zero passage of the burst signal which is detec-ted and supplying a correspoAding correction signal, and that the keying s signal generator is adapted to supply a keying sig- !
nal which relative to the horizontal synchronizing 3 pulse has a delay equal to a first time interval which is variable depending on the correc-tion sig-nal.
The step in accordance with the lnvention ensures that the beginning of the keying signal is always situated halfway between two consecutive zero passages of the burst signal regardless of~
changes in the posi-tion of the horizoAtal synchro-', ~ jt~ ~ : 27.9.76 nizing pulse relati~e to the burst signal r thus po-sitively ènsuring that always the same zero passage of said burst signal~functions as pilot signal for the time error d0tection.
, The invention is by no means limited to the use of the colour burst signal as s-tated here~
inbefore with respect to the NTSC colour television signal. As an alternative an additional burst~slg-nal may be added to the television ~ignal to be re-corded in an appropriata time inter~al during each line period. An example of this is the insertion of a burst signal during the time interval of the ho-rizontal synchronizing pulse 9 resulting in a burst signal which i5 superimposed on said horizontal ~, - - 15 synchronizing pulse, which possibility is describ-ed in "Consumer Electronics~', 5-1-76, pages 54 and further. The use of such an additional burst signal , is of particular importance when utilizing ~ PAL-standard colour television signal, because in this case the colour burst signal itself cannot be used .
~ for the, describ0d time error detection owing to .
the standard coupling with the llne frequency.
, Although~the invention is by no means limited to such a system, the~invention will be described hereinafter on the basis of an optical , read system ~or disc-shaped record carriers. In the drawing: ~ ~
~ ' , - - ' , ~ 8 '' - `: :
' 27.9 .76 Zj~;t~;3 Fig. 1 shows such an optical read system, ~ig. 2 schema-tically shows t~e known time error measuring system, and Fig. 3 shows the signals associated with this system.
Fig. 4 shows the time error measuring system in accordance with the invention, and Fig. 5 sho~s the associated signalsO
Fig. 6 shows a practical embodiment of the ~eying signal generator utilized in the apparatus - in accordanoe with the invention.
Fig. 7 is an extension of the measuring system, and Fig. 8 represents an additional burst sig-nal on the line synchronizing pulse.
The read apparatus shown in Fig. 1 is suit-able-for reading a disc-shaped rccord carrier 1, on whose upper surface tracks are formed (e.g. as turns of a spiral) in which the information is recorded a relief pattern. This track form and method of cod-ing on the record carrier is irrelevant for the principle of the invention~ The disc-shaped record carrier 1 is rotated in a direction V1 with the aid of a motor 2 with a disc-supporting spindle 3, which proJects through a central opening 4 of the record ca~rier 1~
~he optical system for reading the record _ 9 27,9,76 6'~
carrier 1 is accommodated in a housing 5. This optical system first o~ all cosnprises a radiation source 6.
This radiaticn source ~mits a radiat:ion bearn a1 which via a semi-transparent mirrcr 7 impinges on a mirror 8 and is reflected by this mirror 8 as a radiation beam a2. This radiation beam a2 is reflected as a radiation beam a3 by a mirror 9, which beam is fo-cussed by a lens 10 into the scanning spot P on the upper surface of the record carrier 1. This upper surface of the record carrier 1 is reflecting, so that a radiation beam al~ (which is modulated hy the information) is reflected and via the lens 10 impinges on the mirror 9 is reflected as a radiation beam a5 and is then reflected by the mirror 8 as a radiation beam a6. This radiation beam a6 impinges on the semi-~ transparent mirror 7 so $hat a part of this radiation bcam is re~lected as a radiation beam a7 which is in-cident on a read detector 11. This schematically re-presented read detector 11 detects the information contained in the radiation beam a7 and supplies a corresponding electrical signal to an output ter-minal 12.
This signal at the output terminal 12 is applied to a decoding de~ice 18, which converts the applied television signal (which is coded in a spe-ciflc manner) into a standard televislon signal - which iB available at a terminal 19. It is obvious . , .
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27.9.76 ~ Z~7~
that the design of this decoding device is determined by the coding of the television signal used during recording on the record carrierO If, for example, a composite system is employed,~in which the complete standard television signal (i~e. the complete combi-nation of lum.inance and chrominance signals~ is added to a carrier wave as frequency modulation, this de~
coding device employs a frequency d~modulator. The coding method is irrelevant for the principle of the invention.
In order to ensure that th~ scanning spot P
is always incident on the information track on the record oarrier, a radial tracking control system is provided with which the radial position of the scan-ning spot is controlled. This control system first of all comprises a measuring detector for measuring the radial position of the scanning spot P. For the sako of simplieity it is assumed that this measur-ing detector-is included in the read detector 11 a~d that it supplies a control signal to a terminal 13. Examples of systems with which this radia1 po-sition of the scanning spot can be measured can be found in the said United States Patent Specifica-tion No. 3,381,086, United States Patent Specification No. 3,876,84~ (PHN. 6292), and Canadian Patent Spocification No. ~57,o67 (PHN.5503). rnis control signal at the terminal 13 is applied to a drive .
"' . , .
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P~IN 8201C
27.9.76 IZf~
means 15 by which the mirror 8 can be pivoted in the direction V2 about the axis 14. By pivoting this mir-ror 8 the di.rection of the beam of radiation a1 is changed and thus the radial position o~ the scanning spot P. From the avera~e angular position of this mirror 8. a second control signal i5 derived for a drive means 16 by which the housing 5 can be moved in a radial direction V3.
Owing to the variations in the speed o.~ the drive motor 2 and/or eccentricity o~ the opening 4 relative to.the centre of the record carrier 1, the read-out television signal exhibits time errors, which are dis-turbing, particularly with respect to the colour reproduction. In order to correct these .15 time errors a time error correction system is includ-ed in the optical read system. This ti.me error cor-rection is achieved with the aid o~ the mirro 9 which is rotatable by means of a drive element 17 in a direction V4. By pivoting the mirror 9 in this : 20 direction the scanning spot P is moved in the longi-tudinal direction o~ the in~ormation track on the . record carrler 1, so that said time error -can be corrected.
The control signal required ~or said drive element 17 i9 obtained with the aid of a time error detector 25. The decoded television signal is applied to this time error detector. The time error detector .
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PI-IN 820iC
27.9.76 ~ 7~
25 first of all comprises a device 20 for extracting a pilot signal suitable for time error measurement from said decoded television signal. The circuit ar-rangement of this device 20 will be described later.
The pilot signal, which has been extracted by the device 20 and whose frequoncy and phase represent the time errors, is applied to a phase compa-rator circuit 21, which also receives a reference signal from an oscillator 22. The measured phase difference between the two signals is then a measure of the time errors and is used to ~ tain the desired control signal for the drive element 17 via a control am-plifier 23. The Figure also shows a possibility o.f deriving the control signal f`or the drive motor 2 for the record carrier 1 Prom said time error de-tector 25 via a control amplifier 24. It is evident that any other pilot signal contained in the .tele- ¦
vision signal may also be used for thls purpose, because the two control s~stems need not comply with the same requirements.
The previously mentioned known form of the devicc 20 for extracting a suitable pilot signal is schematioally shown in Fig. 2, whilst Flg. 3 shows the associated signals~ In order to clarify the operation of the device of Fig. 2 reference is first of all made to Fig. 3a. Fig.~3a shows a ho-rizontal synchroni~,ing pulse S followed by the , PHN 8~01C
27.9.76 2~3 colour burst signal B in accordance with the NTSC-standard on an enlarged scal~. To simplify the draw-ing the time scale has been in-terrupted within the hori~ontal synchronizing pulse. The ~requency o~ the colour burst signal B is an odd integral mul-tiple of' hal~ the line frequency. This means that exactly one line period a~ter a specific ~ero passage of -this colour burst signal another zero passage of ' the colou~ burst signal corresponding to the next line peri.od appears. This is utilized in the de-vice of Fig. 2.
This device has been adapted to detect al-ways the same zero passage of the colour burst sig-- nal, so that a line-sequential pilat signal is ob-tained, which on the one hand results in a wide con-trol ran,ge of the time error correction device and on the other hand enables accurate time error measure-.
ments to be made. This accuracy result from the fact that the edges of the colour burst signal are very steep, thus enabling the relevant zero passage to be detected in an accurate manner, whilst moreover the disturbing influence of noise which is super-imposed on the read-out television signal can sub-stantially be reduced in a simple manner with this zero passage detection 'by previously passing t~is , - burst signal through a narrow-band ba,nd-pass fil-' ' ter.
.
. PHN 82010 ~,7~3 27,9.76 In order to ensure tha-t always the same zero passage o~ the colour burst signal is detected, -tho device 22 of Fig. 2 comprises a pulse gcnerator 38, This pulse generator 38 is triggered by -the horizon-tal synchronizing pulse, specifioa:l.ly by the leading edge thereo~ 9 between -the horlzonta.l blanking level VB and the peak level VT, which synchronizing pulse is extracted from -the decoded -television signal.
For this purpose the device 20 includes a low-pass 1-0 filter 36, which is connected to the input terminal 31 and to a.sync separator 37 which is connec-ted to this low pass filter 36, which separator in known manner detects the horizontal synchronizing pulses S, for example with a threshold value detector with a threshold value VD, and supplies pulses (see Fig.
3c) which coincide with the synchronizing pulses to the keying signal generator 38. This keying sig-nal generator 38 comprises a first monostable multi-vibrator 39 which is triggered by these horizontal synchronizing pulses and in response thereto supplies pulses T(see ~ig. 3d)~ the duration of -these pulses T being selectsd so that the trailing edge of these pulses T appsars within th.e timo interval occupied . by the burst signalO This pulse T is applied to a second monostable multivi~rator 40, which is trig-gered by the trailing edge of this pulse T and in response thereto supplies a pulse W (see Fig. 3e).
, _ . :
PIlN 8201C
27.9,7G
~7~3 This pulse W for example has as a pulse width of 140 nanoseconds, ~.e. a half period of the colour burst signa:L~
The output o:~ the pulse generator 38, which supplies this pulse 1~, is connected to a first input 45 of a gate circuit l~1. Ta a ~econd input l~l~ short pulses (see Fig. 3b~ are applied, which represen-t the ~ero passages of the burst signal B. For this purpose the device 20 includes a low-pass filter : 10 32 by means of which the frequency band in which the frequency of said burst signal is situated is extracted from the television signal applied to the input terminal 31. The extracted signal is amplifie~
and limited with the aid of a limiter circuit 33 in order to obtain a square wave signal and the zero passages of this square wave signal are deLected . with the aid of a de-tector 34, The detector 34 operates in an absolute manner in the case of an NTSC colour television signal, i,e, the detector 34 supplies an output pulse upon each zero passage of the burst signal, regardless of the sign of the slope, This is necessary in the case of an NTSC
colour television signal because the burst signals B and Bt in two consecutive line periods are in phase opposition (see Fig, 3a) o~ing to the fact that~the chrominance carrier ~requency is locked -to half the line frequency~
.
~; , ' .
27.9.7G
~ 3 The gate circuit 41 (perI'orms an AND-function for the signals at its inputs ll4 and 45, which means that the output pulse of thls gate circui-t 1-~1 f;~
(see Fig. 3b) always corresponds to that pulse from the æero passage detector 34 wh:ich appears within the time interval of the pulse W from the pulse ge-nerator 38. As a resul-t, a pulse is generated line-sequentially (Fig. 3f) which can be utilized as a pilot signal for time error measurement. If desired, 10 ~ this pulse may also be applied to a monos-table multi-- ; Yibrator 42, which derives pulses with a specific pulse width therefrom, which are th0n a~ailable at the output terminal 43 and may be applied to the compara-tor circuit 21 of Fig. 1 as a pilot signal.
If the pulse width selected for the pulses supplied by the monostable multivibrator 42 is greater tllan - the pulse width of the pulses W frorn the pulse ge-~ nerator, substan-tially any pulse width may be used ; for these pulses W, because then only the first pulse from the zero passage detector 34 will re-sult in an outpu-t pulse of the multivibrator 42 during a pulse W.i In order to increase the reliability of operation of the device it is useful to include a detectQr 35 which is connec~ed to the low-pass filter 32 and which detects the presence of a colour burs-t signal. This detector conscquently ~ ~ .
, PllN 8201C
27.9.76 Y~ 3 supplies an output pulse as soon as and as long as this colour burst signal is present. This output pulse o:f the colour burst detector ls also applied to the gate circuit 1~1 (input 1~6), so 1;ha-t this gate circui-t can only supply an output pulse in the pre-sence of a colour burst signal. This additional cir-cuitry caters for the fac-t that during the vertical flyback period of the television signal a nwllber of picture lines contain no colour burst signals. Should the zero passage detector 34 supply a pulse within the pulse W, despite the absence of a colour burst signal (for example owing to the occurrence of noise) this does not give rise to an (erroneous~ pulse at the output of the gate circuit.
The effect of -this ~dditional circuitry be-comes more apparent ~len taking into consideration that in the most frequently used version o~ the com-parator circuit 21 a "hold effect" occllrs if no pul-ses are supplied by the pilot tone separator. This comparator circuit 21 generally operates with a ; sawtooth-shaped re~erence signal from the oscilla-tor 22, which signal is then sampled at instants which are defined by the pulses of the pilot tone sepàrator, This sampled value is subsequently re-tained until the next sampling oocurs. As long as the pilot tone separator 20 supplies no pulses, i.e.
during a portion of the vertical flyback period, the : , .
P~IN 820lC
27.9.76 'YZ~
last sample value is retained as a control signal for the time error correction system.
However, an erro~eous pulse from the pilot tone separator during the vertical flybacl~ perlod would control this time error correction system in a completely incorrect mannor. It is true that af-ter the occurrence of ~some picture lines having colour burs-t signals, this time error correction system will be pulled in again, but as this is ob-viously involves a delayed response, it could still give rise to disturbances in the displayed picture.
In order to minimize the time during the vertical flyback period that no measuring signal is available it is of course also possible to add additional burst signals to the television signal ; to be recorded during this vertical flyback period.
A problem associated with the prcviously described method of generating a suitable pilot - signal for time error measurements is caused by the faot that the position of the horiæon-tal synchroniz-ing pulse relative to the burst signal is not accu-- rately defined. This has various causes. First oP
' all, the accuracy with which the horizontal syn~
chronizing ~ulses are generated prior to recording of the -television signal is liniited. Furthermore, as previously stated, the accuracy with which these - horlzontal synchronizing pulses can be detected dur-- .
'~
27.9,76 ~Z~3 ing reproduction is limited and in this respect the susceptibility to noise plays a part. Furthermore, -the phase relation bet~een the hor:izontal synchro-nizing pulses and tlle colour burst signal is dis-turbed, since th:is b~rs-t signal has been passed through a band-pass filter.
As the keying signal 1~ is directly derived from the detected horizontal synchronizing pu]se this means that the position of this keying signal within the time interval of the burst signal is - neither accurately defined. In the ideal case the instant at which said keying signal W starts, i.e.
the position of the leading edge, ls situated exactly halfway between two consecutive zero passages of the burst signal. If this keying signal W is now shifted ; owing to the inaccuracy of the position of the hori-;
zontal synchronizing pulse, it may for example happen that the leading edge of this keying signal does no~
appear until after the desired ~ero passage of the burst signal, as is shown in Fig. 3h~ In that case the next zero passage of the burst signal is then utilized for generating the pilot signal (see Fig.
31). This change from the one zero passage to the ~: next zero passage for the generation of the pilot signal manifests itself in the tims error detection ; as a time ~rror of 140 nanoseconds, namely -the in-t0rval between these two zero passages, thus result-_ 20 2~.9.76 q;~73 ing in an incorrect time error measurernent and conse-quently in an incorrect timo error correction.
This problem is avoided owing to the step in accordance with the invention. The step in ac-cordance with the inventioIl main:Ly affects the ci.r-cuit arrangement of th~ Iseying signal generator 38.
In order to explain the step in acoordance with the invention ~ig. 4 schematically sho~s the circuit ar~
rangoment of the pulse generator 38 together with the ga-te circuit 419 which circuits form part of the device of Fig. 2.
The pulse generator 38 sho~n in Fig. 4 oom-prises a monostable niultivibrator 51 to whose input 54 the extracted horizontal synchron~zing pulses supplied by ~he sync separator 37 are applied ; ~ (FigQ 2). This monostable multivibrator 51 supplies ~a pulse T'which is applied to a set input 55 of a , : multivibrator 52, whose output is connected to the input 45 of the gate circuit 41. The pulse from the :!
. zero passage detector 34 is applied to the input 4l~
o~ the gate circuit 41 so as to be keyed out with the : aid of~said gate circuit, after which it is applied to the reset Input 56 of` the multi~i'brator 52, as the case may be after'processing by the monostable ,~ 25 multivibrator 42. Howcver, the pulse width of the : , pulse T which is supplied by the monostable multi-- vIbrator 51 iS~ not cDnstant but is ~ariable depend-`
: ~ ~ ing on a correction signal ~hich is fed to a control . iDpUt S7 o~ this monostable multivibrator 51.
, - 21 - '~
. . .
~. ' -- ' -'. . '. '. . '; . '' , ' '-, :.
P~IN 8201C
27.9.76 ~7~
The operation of the circuit will now be described with reference to Fig. 5. Fig. 5a shows a number of pulses which are supplied by the zero pas-sage detec-tor 34 and which thus represent the zero passages o~ the burst signal. Fig. 5b shows a pulse T supplied b~ the monostable multivibrator 51, whose leading edge again coincides with the leading edge of the horizontal synchronizi.ng pulse and whose trailing edge of situated within the time interval occupied by the burst signal. In the ideal situation the trailiDg edge of` this pulse T should occur at an instant t exactly halfway between two successiv~
zero passages of the burst signal. However, it is assumed that owing to the inaccuracy of the horizon-tal synchronizing pulse this trailing edge appears at an instal~t t1. This trailing edge of the pulse T triggers the multivibrator 52, so that said mul tivibrator chan~es over (~ 5c). When at the in-stant t2 a pulse Q from the zero passage detector i9 applied to the gate circuit 41 a pulse (Fig. 5d) is produced at the output of the monostable multi-vibrator 42, which pulse is applied to the reset ,~ input 56 of the multivibrator 52. Th~s pulse resets the multivibrator 52 to its original state at the instant t2, so that the output signal of this mul-.~ tivibrator.is the puise W shown in Fig. 5c.
.~ .
'' :
' - . - 22 ~ ' ' ' ' ~
. PHN 8201C
27.9.76 From the Figure it is evident that the pulse width t o~ this pulse W corresponds to the time in-terval t2-t1, so that it is a measure o~ the po~i-tion of the trailing edge of the pulse T between tho two c~ns0cutive zero passages of the burs-t signal. T.his data is utilized by the invention or automatically correcting the positi~on of the trailing edge o~ the pulse T. The pulse width t~ of -the pulse W is measur-ed with the aid of a measuring circuit 53 and convert-ed into a correction signal ~or the monostable multi-vibrator 51. In the example of Fig. 5 this correction signal will result in a reduction of the pulse wid-~h ; Or the pulse T, in such a way that the trailing edge ., . of this pulse T is moved towards thQ instant to.
. ~ 15 (Fig. 5e), which in its turn results in a pulse W
from the multivibrator 52 in accordance with Fig.
~f.
Thus it is achieved that the leading edge - of the keying signal W is always controlled towards . 20 a position halfway be-tween two consecutive zero passages of the burst signal, so that symmetrically about this position a maximum tolerance is permis-sible without giving rise to an erroneous time error-. I , ,I mea~urement. The multivibrator 52 preferably tak0s the form of a monostable which in the absence of a reset signal at the input 56 is automatically reset . ' ' ' . ' . :
~ 3 P~IN 8201C
` 27.9.76 :~'7~ 3 .' after for example 140 nanoseconds A practical embodiment of the monostable multivibrator 5I in conjunction with the measuring circuit 53 is shown in Fig. 6~ The measuring circuit 53 comprises a capacitance C2(4.7/u~) which is con-nected to a voltage source V2 and which is charged via a resistor Rl~(220 kohms). The charge of this capacitance C2, i.e. the voltage acrpss it, depends ?
: on the signal on the base of a transistor T1. The ~, base of the transistor T1 receives the output pulse W of the multlvibrator 52 and this transis.tor con-ducts for the duration o~ this pulse, so that the voltage across the capacitance C2 Is determined by `. the pulse duration of this output pulse W of the : ~ 15 multivibrator 52. The voltage across the capacltance : ~ . C2 is applied to an emitter~follower T2 and with the aid of a resistor R3 (150 kohms) it is converted in-to a control current which is appliod to the control .terminal 57 of the monostable multivibrator 51.
This monostable multivibrator 51 comprises an integrated multivibrator circùit 58 of the type SN 741e3 (Sign0tics), whose time constant, i.e.
pulse duration, is determined by the capacitance , C1(3300 pF) and the resistors R1(2.2 kohms) and : 25 R2(6.2kohms). As the control input 57 is connected : ~ to this capaci~ance C2 the charge on this capacitance- -.
. ~ .
C2 and thus the time constant depend on the correction ' , .
2l~ _ .
PHN ~201C
27.9.76 ~r7Z~73 current. By dimensioning the resistors and capacitan-ces as specified it is achieved that the pulse dura-tion of the output pulse of this rnonostable multlvi-brator circuit 58 as a ~m~tion o~ the correction current can ~ar~ minimum appro~ 140 Danoseconds, i.e. ma~imum hal~ the period of the NTSC colour .
burst signal. It is obvious that many modifications to this circuit arrangement are possible. For exam-ple, it is also possible to use a variable delay means instead of -the monostable multivibrator.
Fig. 7 shows a variant of the circuit ar-rangement of Fig. 4, corresponding elements being denoted by the same re~erence numerals. The output signal of the limiter circuit 33 in this circuit arrangement is not applied directly to the ero passage detector 34, but is applied both directly to an input 64~and via an inverting amplifier 61 to an input 63 of a two-position switch 6~ whose master contact 65 is connected to the zero passage detector 34~. This switch 62 i5 controlled by a control cir-cuit 66 whlch receives the horizontal synchronizing pulse train supplied by the sync separator 37 at an :, :
input 67. This control circuit 66 then supplies a symmetrical control signal of half the line fre-quency to the switch 62 so that this switch is changed over from line to line. Thus~ it is ensured that the colour burst signals ~ consecutive lines, 27.9.7G
~ 6~3 which are applied to the zero passage detector 34' always have the same phase with respect to each other, This means that this zero passage detector 34l no longer need be of the absolu-te type, as in tho ver sion in accordance with Fig. 4, but should merely respond to the zero passages which occur in the case of one specific sign of -the slope of the colour burst signàl. This moans that this zero passage detec~
tor 34' may then taka the form of a simple monostable multivibrator.
As pr0viously stated, the in-vention is by no means limited to optical read apparatus, but is also applicable.to read apparatus for a magnetic re-cord carrier in the form of a tape. ~Irthermore~ the circuit arran~ement of the time error.correctivn sys-tem is not limited:to the system described, In prin-cipl0, any suitable time error correc-tion system, whether electromechanical or electronic, may be used, the ultimate choice being generally determined by the ., ;
type of read system.
Furthermore, the in~en-tion is not limited to - the coding system des~ribed by way of example, in i which a complete standard NTSC colour television sig-, nal is frequency modulated on a carrier wave. The invention may for example equally be used with cod- ;
îng systems in which, during recording, the c~romi- ~
:
~ nance signal is extracted and transposed -to a lower :
: frequency band~ i.e. is record.0d as a modulation of .~ , - ' ' .
.
27~9.76 .
a separate chro~ninance carrier wa~e, whilst the lumi-nance signal lS frequcncy modulated on a carrier wave of comparativel.y high frequency. In such coding 5yg-tems the ~requency of the s~pa~ate chrominance carrier is generally arl integral multiple of half the line f`requency. During reproduction the read-out chromi-nance signal is than re-transposed to the standard frequency band by mixing it with a suitable mixing frequency, so that again a standard NTSC or PA~
colour television signal is obtained. By ensuring that the mixing frequency has the same time errors as the read-out chrominance signal, the influence of these timing errors on the ultimately obtained standard colour television signa~l is substantially : 15 reduced. By the indicated choioe of the frequency of the separate chrominance carrier it is achieved that ., as pilot tone for producing this ~ixing frequency use can slmply be made of the read-out horiz.ontal synchronizing pulse train as is for example compre-hensively described in United States Patent Speci.fi-cation 3,803,3l~7 (PHN 4978). Instead of this horizon-. ~ .
.~ ~; tal synchronizing pulse train it is then obvious .
that use can also be made of a æero passage of the colour burst signal with the aid of ~ device in ac-J
cordance with the present invention. In that case it ; ~ is also possible to~use.the colour burst signal pre-~ ' ~
..
.
27 . 9 , 7G
'Z6~;~
sent in the colour signal, or an additional burst si.g-nal on the backporch of -the ho:rizonta:L syncllronizing pulses, which has been added -to the luminance signal during recording.
Furthermore it is not necessary to separate the pilot tone from the;...complete decoded television signal (output of decoder 18). Dependent on the cod-ing system this pilot tone could be -sepa~ateds~1ome-where wi'thin the decoding process.
It is to be noted that although the invention will primarily be used to advantage ~or.reading out a colour televislon signal, this invention may also be ~ used for reading out a black-and-white television - signal. For this purpose, it will only be necessary to add burst signals on tha backporch of the horizon-tal s~nohronizing pulses during recording.
Fina].ly, the possibility will be described of adding an additional burst signal to the televi~
sion signal during recording, which burst signal may be utiliz0d for accurately measuring the time : errors during r~production, This possibility is represented in Fig. 8. This Flgure again sho~ys a horizontal synchronizing pulse S of a television slgDal with a horizontal blanking level:VB and a peak level VT. However, prior to recordingl a burst signal E has been superimposed on this hori~
zontal synchronizlng pulse S, i.e. on the peak level -. ' ~ .' , ~ 28 '.~ ' . ' ' ' 27.9.7G
~ 7~
VT thereof. This burst signal L has a frequency which is an integral multiple of half the line frequency and preferably an integral~mllltiple of the whole line frequency.
During reproduction of the recorded tele-vision signal this additional burst signal is ex-tract~
ed, after which in a similar way as described herein-before with respect to the NTSC colour burst signal the positionof a specific zero passage of this addi~
tional burst signal can be detected during each line period and can serve for measuring time errors. ,~
The use of this additional burst signal is of special importance when recording and reproducing a colour television signal which complies with the PAL standard. In this case the colour burst signal cannot simply be used in the described time error measuring system because the frequency ~f said PAL
colour burst signal lS an odd multiple of 1/l~ fH and moreover exhibits a 25-Hz offset.
If furthermore an additional burst signal with a frequency equal to a multiple of the line frequency is used, a~non-absolute zero passage detec-tor may be used for detecting the zero passages, i.e.
a detector which detects only the zero passages which correspond either the positive-going or the negative-going edges. Thus, the time interval within which the beginning of the keying signal should occur is - ~ .
~ 29 27.9.76 ~ 3 doubled compared with the use of the NTSC colour burst signal, because this now corresponds to a f`ull period of' the burst signal. Finally, the use Or this additional burst signal superimposed on the horizontal synchroniz-ing pulse has the advantage -that -the first -time i.nter-val, i.e. the time between the leading edge of' the horizontal synchronizing pulse and the koying signal is substantially shorter than when the colour burst signal is ùsed, This shorter time interval can be realized more accurately with the aid o~ multivibrator .
cir~uits, which adds to ths reliabiLity of ths systsm.
,~
.
. ..
~, .
' 1~ ., . ~_ 30 _ .
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An apparatus for reading a record carrier on which a television signal is recorded, which signal comprises horizontal synchronizing pulses and burst signals which are coupled to these horizontal synchro-nizing pulses, which burst signals consist of a num-ber of periods of a carrier wave with a frequency which is an integral multiple of half the line frequency, which read apparatus is provided with a time error correction device for correcting time errors in the read-out television signals and a time error detector for detecting said time errors and supplying a corres-ponding control signal to the time error correction device, which time error detector comprises a keying signal generator which is triggered by the horizontal synchronizing pulses, which generator supplies a key-ing signal which is delayed by a first time interval relative to said horizontal synchronizing pulse, said first time interval being such that the beginning of the keying signal each time lies within the time in-terval occupied by the burst signal, and furthermore a zero passage detector for detecting the first zero passage of the burst signal which appears after time beginning of said keying signal, characterized in that the time error detector comprises a measuring circuit for measuring the time interval between the beginning of this keying signal and the next zero passage of the burst signal which is detected and supplying a corres-ponding correction signal, and that the keying signal generator is adapted to supply a keying signal which relative to the horizontal synchronizing pulse has a delay equal to a first time interval which is variable depending on the correction signal.
2. An apparatus as claimed in Claim 1, charac-terized in that the keying signal generator comprises a first and a second multivibrator, the first multivi-brator being of the monostable type and being provid-ed with a set input to which the horizontal synchro-nizing pulse is applied, a control input to which the correction signal is applied, and an output at which an output pulse becomes available with a pulse dura-tion which depends on the correction signal, whilst the second multivibrator has a set input which is connected to the output of the first multivibrator, and which multivibrator is triggered by the trailing edge of the output pulse of the first multivibrator and produces the keying signal at its output.
3. An apparatus as claimed in Claim 2, charac-terized in that the second multlvibrator has a reset input, to which a pulse which is determined by the detected zero passage of the burst signal is applied for resetting this second multivibrator.
4. An apparatus as claimed in claim 3, characterized in that the second multivibrator is automatically reset after a fixed time interval after the beginning of the keying signal.
5. An apparatus as claimed in claim 4, characterized in that in the case that a burst signal with a frequency which is an odd multiple of half the line frequency is used the second multivibrator is automatically reset after a time interval which substantially corresponds to half the period of said burst signal.
6. An apparatus as claimed in claim 4, characterized in that in the case of a burst signal with a frequency which is an integral multiple of the line frequency the second multivibrator is automatically reset after a time interval which substantially corresponds to the period of said burst signal.
7. An apparatus as claimed in claim 3, 4 or 5, character-ized in that the output signal of the second multivibrator is applied to the measuring circuit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7512186A NL7512186A (en) | 1975-10-17 | 1975-10-17 | TIME ERROR CORRECTION SYSTEM FOR A DEVICE FOR READING A REGISTRATION CARRIER. |
| NL7610506A NL7610506A (en) | 1976-09-22 | 1976-09-22 | TV signal reproducing system with synchronization correction - has generator delivering switching signal delayed w.r.t. line synchronization pulse at interval dependent on correction signal |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072673A true CA1072673A (en) | 1980-02-26 |
Family
ID=26645156
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA263,410A Expired CA1072673A (en) | 1975-10-17 | 1976-10-14 | Apparatus for reading a record carrier |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5250120A (en) |
| AR (1) | AR210616A1 (en) |
| AU (1) | AU507895B2 (en) |
| CA (1) | CA1072673A (en) |
| DE (1) | DE2646098C3 (en) |
| ES (1) | ES452436A1 (en) |
| FR (1) | FR2328341A1 (en) |
| GB (1) | GB1563326A (en) |
| HK (1) | HK52180A (en) |
| IT (1) | IT1073035B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56166686A (en) * | 1980-05-28 | 1981-12-21 | Pioneer Video Corp | Timing axis variation elimination device of video disk reproducer |
| FR2489063B1 (en) * | 1980-08-22 | 1986-09-26 | Victor Company Of Japan | TRAVEL COMPENSATION DEVICE IN A ROTARY RECORDING MEDIUM REPRODUCING APPARATUS |
| JPH0620293B2 (en) * | 1986-09-17 | 1994-03-16 | パイオニア株式会社 | Time axis error correction device |
-
1976
- 1976-10-13 DE DE19762646098 patent/DE2646098C3/en not_active Expired
- 1976-10-14 GB GB4273676A patent/GB1563326A/en not_active Expired
- 1976-10-14 IT IT2832576A patent/IT1073035B/en active
- 1976-10-14 CA CA263,410A patent/CA1072673A/en not_active Expired
- 1976-10-15 FR FR7631102A patent/FR2328341A1/en active Granted
- 1976-10-15 ES ES452436A patent/ES452436A1/en not_active Expired
- 1976-10-18 JP JP51124767A patent/JPS5250120A/en active Granted
- 1976-10-18 AR AR26513976A patent/AR210616A1/en active
- 1976-10-25 AU AU18939/76A patent/AU507895B2/en not_active Expired
-
1980
- 1980-09-18 HK HK52180A patent/HK52180A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB1563326A (en) | 1980-03-26 |
| ES452436A1 (en) | 1977-11-01 |
| IT1073035B (en) | 1985-04-13 |
| DE2646098A1 (en) | 1977-04-21 |
| DE2646098B2 (en) | 1978-03-23 |
| FR2328341B1 (en) | 1981-12-04 |
| AR210616A1 (en) | 1977-08-31 |
| JPS5250120A (en) | 1977-04-21 |
| AU1893976A (en) | 1978-05-04 |
| DE2646098C3 (en) | 1978-11-09 |
| AU507895B2 (en) | 1980-02-28 |
| JPS5424251B2 (en) | 1979-08-20 |
| FR2328341A1 (en) | 1977-05-13 |
| HK52180A (en) | 1980-09-26 |
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