JPS5941635B2 - Jitter correction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a jitter correction device for correcting jitter in color television signals recorded on a VTR.

Color television signals recorded and reproduced on a VTR (video tape recorder) generally have time axis fluctuations, or so-called jitter, due to expansion and contraction of the tape, uneven rotation of the drive system, and the like.

In order to correct such jitter, conventional home VTRs
In this case, the luminance signal is FM-modulated, and the color signal is low-frequency converted using a 3.58 MH2 subcarrier for recording and reproduction. The jitter of the luminance signal is corrected via a variable delay line, and the jitter of the color signal is corrected via a phase control circuit. However, in the above-mentioned correction means, a time lag occurs between the luminance signal and the color signal. For this reason,
This caused color shift in the reproduced image. Therefore, it has been considered to compare the phase of the horizontal synchronizing signal of the reproduced color television signal and the oscillation frequency of the flywheel oscillator of the recording/reproducing mechanism system, and to correct the jitter based on the comparison result.

However, with this correction means, the configuration of the device becomes complicated and expensive. Furthermore, jitter at sufficiently low frequencies could not be detected well, and some color unevenness still remained.
In order to effectively correct this remaining color unevenness, or residual jitter, an extremely high-precision flywheel oscillator is required.
It was technically difficult. Furthermore, when large skew distortion occurs, residual jitter remains and no countermeasures can be taken. The present invention has been made in consideration of these circumstances, and its purpose is to be able to effectively correct jitter from low frequencies to high frequencies with a simple configuration, and to eliminate skew distortion. It is an object of the present invention to provide a jitter correction device that is sufficiently effective against the above problems and can obtain good reproduced images without color shift.

That is, the jitter correction device according to the present invention controls the color television signal recording/reproducing system, that is, the capstan servo and head servo, based on the reference signal generated from the reference oscillator built into the VTR. , removes jitter at low frequencies.

In order to deal with jitter at high frequencies, a signal is recorded based on the reference signal, and the reproduction signal is delayed and controlled based on a phase comparison result between a synchronization signal extracted from the reproduced signal and the reference signal. The correction is made according to the following. According to the apparatus of the present invention, since recording and reproduction of signals are performed under exactly the same frequency conditions, the frequency of the subcarrier signal of the video signal does not change even after reproduction.

This is because all VTRs are controlled using a fixed reference oscillator as a reference. Therefore, color unevenness caused by skew distortion can be more effectively corrected than when correction is performed using a flywheel oscillator as a reference. - No special circuit is required to deal with the above-mentioned skew distortion. Moreover, the configuration can be extremely simplified. Embodiments of the apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the apparatus of the present invention.

A television signal captured by an ITV or a television signal transmitted via an antenna is separated into a luminance signal Y and a carrier color signal via a color separation circuit (not shown). The separated luminance signal Y is sent to the FM modulator 1
The signal is input to FM modulation. Further, the carrier color signal is inputted to the frequency converter 2, subjected to low frequency conversion by a first reference signal with a frequency of 4.27 MHz supplied from the reference oscillator 3, and outputted as a signal with a frequency of 688 kHz. The signals outputted via the FM modulator 1 and the frequency converter 2 are input to an adder 4 and are combined. This composite signal is then applied to the magnetic head 7 of the video recording system 6 via the switch 5 and recorded on the magnetic tape. The video recording system 6 includes a capstan servo, a head servo, etc., and operates on the basis of a frame frequency of 30 Hz, which is separated from the television signal. Note that 8 in the figure is a servo circuit of the video recording system 6. On the other hand, the signal recorded in the video recording system 6 is reproduced by the magnetic head 7 and outputted via the switch 5.

This output reproduced signal is input to a CCD delay line 10 together with an FM demodulator 9. A synchronizing signal separator 11 is connected to the FM demodulator 9, and the regenerated FM demodulator 9
The horizontal synchronization signal of the television signal is separated and extracted from the signal demodulated via the . This separated and extracted horizontal synchronizing signal is input to a phase comparator 12, where it is phase-compared with a second reference signal having a frequency of 15.75 KHz emitted from the reference oscillator 3. The comparison result by this phase comparator 12 is input to the CCDl drive oscillator 13,
A CCD drive signal having a frequency corresponding to the above comparison result is output. This CCD drive signal operates the CCD delay line 10. The CCD delay line 10 delays and outputs the reproduced signal for a time determined by the frequency of the applied CCD and drive signal. The reproduced signal outputted via this CCD delay line 10 is separated into a luminance signal component and a color signal component by a separation circuit (not shown). The luminance signal component is demodulated via the FM demodulator 14. Further, the color signal component is input to the frequency converter 15, and is subjected to high frequency conversion based on the first reference signal having a frequency of 4.27 MHz supplied from the reference oscillator 3. The carrier color signal that has been high-frequency converted and restored to its original frequency and the demodulated luminance signal Y are input to an adder 16 and are combined. This combined color television signal is supplied to a television monitor (not shown) to display a reproduced image. By the way, the reference oscillator 3 is, for example, 17.07
A crystal oscillator 17 having an oscillation output (original oscillation signal) of 2 MHz, and a frequency divider 1 that divides the oscillation output into 1/4.
8. Frequency dividers 19 and 2 connected in series divide the oscillation output by 1A085 and further divide the frequency by 1//525.
It consists of 0.

Thus, the frequency divider 18 emits a reference signal with a frequency of 4.27 MFIz, which is supplied to the frequency converters 2 and 15 described above. Further, the frequency 15.75 for phase comparison is supplied from the frequency divider 19 to the phase comparator 12.
A KHz reference signal is generated. Furthermore, the frequency divider 20 issues a third reference signal with a frequency of 30 Hz to the servo system. Note that each of the frequency dividers 18, 19, and 20 is constructed of a flip-flop circuit or the like. According to the device configured in this way, it is possible to record and record color television signals.
Reproduction is performed based on the reference signal, and the signal state does not change between recording and reproduction.

Therefore, no jitter occurs at low frequencies, and the frequency of the color subcarriers is also kept constant. Furthermore, jitter at high frequencies is detected from phase comparison of the horizontal synchronizing signal extracted from the reproduced signal. Based on this detection result, both the luminance signal component and the color signal component are delayed and corrected for jitter. Therefore, unlike conventional devices, there is no time lag between the luminance signal and the color signal, and as a result, no color shift or color unevenness occurs. That is, as shown above, in an extremely simply configured device,
A very effective jitter correction is made. Furthermore, since jitter correction is performed over a wide frequency band, there is no adverse effect due to skew distortion, and there is no need to add any special circuit. By the way, in the apparatus configured as described above, the capstan servo and the head servo must always maintain a constant relationship during reproduction.

That is, there must always be a constant time difference between the synchronization signal in the reproduced luminance signal and the reference horizontal synchronization pulse (reference signal), regardless of load fluctuations or temperature changes. If stable operation is expected at all times when variable time control is performed for a maximum of one horizontal scan, the permissible change range must be less than 1/10 of the horizontal scan. Therefore, the above conditions can be simplified by configuring the reference oscillator 3 as shown in FIG. 2, that is, by performing phase modulation. The reference oscillator shown in FIG. 2 will be explained with reference to the signal waveform diagram shown in FIG.

This circuit detects the phase relationship between the reproduced horizontal synchronizing signal and the reference horizontal synchronizing pulse, and controls the phase relationship to be kept constant. That is, the reference signal for frequency conversion (4.27L0) and the reference signal for servo control (30
Hz) are similarly generated by the frequency dividers 18, 19, 20 described above. Here, the oscillation output of the crystal oscillator 17 is input via an OR circuit 21 to an up terminal UP of an up/down counter 22 which divides the frequency by 1/1085. The output of this up-down counter 22 is output as a reference signal, that is, a reference horizontal synchronizing pulse. Further, this reference synchronization pulse is supplied to monostable multivibrators 23 and 24 connected in series. The monostable multivibrator 23 has a time width of T1 by inputting a synchronizing pulse.
The monostable multivibrator 24 is activated by the trailing edge of this output. This monostable multivibrator 24 outputs a pulse signal with a time width T2. The outputs of these monostable multivibrators 23 and 24 are supplied to AND circuits 25 and 26,
A logical AND is performed with the reproduced horizontal synchronization signal. This ANDed signal is applied to an up terminal UP and a down terminal DN of an up/down counter 27 which performs I/N frequency division. The carry signal of the up-down counter 27 is input to the up terminal UP of the up-down counter 22 via the OR circuit 21, and the borrow signal is input to the down terminal DN. According to such a reference oscillator, when a reference horizontal synchronizing pulse is outputted as shown in FIG. 3a and a reproduced horizontal synchronizing signal as shown in FIG.
output signals as shown in C and d of the figure, respectively.

Therefore, AND circuits 25 and 26 are shown in FIG. 3E and f, respectively.
It emits a signal as shown in . However, if a horizontal synchronization signal is present at position P1, for example, the phase of the reference horizontal synchronization pulse must be advanced. Therefore, by inputting one additional pulse to the up-down counter 22 based on the ANDed signal in the AND circuit 25, its phase is advanced. Conversely, if a horizontal synchronizing signal exists at position P3, the phase is delayed by down-counting the up-down counter 22 by one pulse using the ANDed signal in the AND circuit 26. . Thus, by the action of the up-down counter 22 and the monostable multivibrators 23 and 24, the operating point of the horizontal phase pulse is always controlled to be centered, and a good signal relationship is maintained here. The up-down counter 27 functions to average the ANDed signals of the AND circuits 25 and 26. This action of the up-down counter 27 prevents the phase of the up-down counter 22 from changing every horizontal scan. Therefore, adverse effects such as jitter on the reproduced image due to phase fluctuations of the reference horizontal synchronizing pulse can be prevented. This prevents color unevenness from occurring due to the phase fluctuation. Note that the present invention is not limited to the above embodiments.

For example, as shown in FIG. 4, a pilot signal emitted from a reference oscillator 3 is superimposed on an FM-modulated luminance signal component and recorded, and the pilot signal is extracted from the reproduced signal by a pilot signal extractor 28. do. and,
The phase of this extracted pilot signal and the pilot signal emitted from the reference oscillator 3 may be compared and detected to control the delay. Alternatively, as shown in FIG. 5, the reproduced signal may be separated into a luminance signal component and a color signal component, and the luminance signal component may be demodulated and then subjected to delay control. In this case, since the luminance signal and the chrominance signal are delayed using independent delay lines, it is possible to improve the S/N ratio. In the above embodiment, a CCD delay line is used as the variable delay line, but a surface wave delay line, an LC delay line, etc. may also be used, for example. Further, the circuit configuration of each part of the frequency converters 2, 5, etc. may be designed according to the specifications thereof, and various circuit systems can be applied. As described above, the present invention can be implemented with various modifications without departing from the gist thereof. As described in detail above, according to the present invention, jitter can be effectively corrected from low frequencies to high frequencies with a simply configured device.
Moreover, it is sufficiently effective against skew distortion, and a good reproduced image without color shift can be obtained. and,
It is possible to provide a jitter correction device that has various special advantages, such as not having to maintain the drive of a video recording system at an unnecessarily high precision unlike conventional devices, and being able to reduce the cost of the device.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the device of the present invention, and FIG.
This figure is another configuration diagram of the reference oscillator shown in FIG. 1, FIG. 3 is a signal waveform diagram showing the action of the reference oscillator shown in FIG. 2, and FIGS. FIG. 2 is a schematic configuration diagram showing an example. 1...FM modulator, 2...Frequency converter, 3...Reference oscillator, 6...Video recording system, 8... Servo circuit, 10...
CCD delay line, 11... Synchronization signal separator, 12
... Phase comparator, 14 ... FM demodulator, 15 ... Frequency converter, 17 ... Crystal oscillator, 18, 19, 20 ... ... Frequency divider, 22 ... Up-down counter, 23, 24
・・・・・・Monostable multivibrator, 25, 26・
...AND circuit, 27...Up-down counter.

Claims (1)

[Claims] 1. A reference oscillator that frequency-divides the original oscillation signal to obtain first to third reference signals having a predetermined phase relationship, a modulator that modulates the luminance signal of the color television signal, and a modulator that modulates the luminance signal of the color television signal. a first frequency converter that performs low frequency conversion of the color signal based on the first reference signal, and recording the signals outputted through the first frequency converter and the modulator on a recording medium, means for reproducing the recorded signal; a synchronization signal extractor for extracting a synchronization signal from the signal reproduced by the means; and a synchronization signal extracted by the synchronization signal extractor and the second reference signal. a phase comparator that compares phases; a variable delay line that delays the reproduced signal based on the result detected by the phase comparator; and a variable delay line that delays the reproduced signal based on the result detected by the phase comparator; a demodulator that demodulates a luminance signal component to obtain a luminance signal; and a second demodulator that performs high frequency conversion of a color signal component of the reproduced signal whose delay is controlled by the variable delay line based on the first reference signal. A jitter correction device comprising: a frequency converter; and a servo circuit that controls a signal reproduction speed from the recording medium based on the third reference signal.