JPS62281578A - Correction system for time axis error - Google Patents

Abstract

PURPOSE:To prevent the generation of a time axis error by substituting a part or all of the horizontal blanking period of a recording video signal for a synchronizing signal, inserting a reference phase burst signal in the horizontal blanking period of a video FM signal obtained by changing a frequency and recording in a recording medium. CONSTITUTION:The reference phase is detected by a reference phase detecting circuit 22 every one horizontal scanning period (1H) of a reproducing video signal 5, the phase comparison of a writing clock (Wck) synchronizing with the reference phase before 1H in a phase lock loop 23 and a phase referring signal (Wck/n) obtained by dividing the writing clock (Wck) in frequency into 1/n is carried out, the signal 5 is sampled through an A/D converting circuit 24 by the Wck, converted into a digital signal and written in a memory 21. A signal stored in the memory 21 is read by a stable clock (Rck), converted to an original analog video signal by a D/A converting circuit 25 and a low pass filter 26 and outputted. The writing and reading address of the memory 21 is set by a memory address counter 27.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for correcting time axis errors that occur during playback of, for example, a video tape recorder (VTR).

(Prior art) In devices such as VTRs that use a tape head system as an FM signal transmission path, time axis errors (referred to as jitter) occur during playback and must be corrected. A reference phase signal is added in advance on the recording side.On the other hand, recent research and development of high-definition television is being carried out, and one of the methods for band compression of high-definition television signals is being developed.
M U S E (Multiple 5ub
-Nyquist Sampling Encodin
g) The method is NZ. This MUSE signal is a luminance/chromaticity line time-division color transmission signal, and because a time-compressed color difference signal is inserted into the horizontal blanking period of the luminance signal, the effective horizontal synchronizing pulse width and horizontal blanking period are significantly narrowed. There is. Therefore, this type of MUSE signal is
It is necessary to consider a new jitter correction method when recording and reproducing data.

Conventionally, the following two methods have been announced as jitter correction methods for MUSE signals.

(1) A method of time-compressing the MUSE signal and inserting a horizontal synchronization signal and a burst signal into the empty period (burst insertion section creation method).

(A method in which a small amplitude, single frequency pilot signal is superimposed on the 21MUSE signal (pyro/nod superposition method).

(Problem to be solved by the invention) However, since the burst insertion section creation method requires time compression processing on the recording side, analog/digital (A/D
There is a problem in that processing circuits such as conversion) and D/A conversion are indispensable, leading to an increase in cost. On the other hand, in the pilot superimposition method, since the pilot signal and the MUSE signal are recorded in a superimposed manner, it is necessary to limit the amplitude of both signals, resulting in a decrease in the S/N ratio of the MUSE reproduced signal. In particular, since a sufficient S/N ratio of the pilot signal cannot be obtained during reproduction, time base errors are likely to occur when detecting the reference phase, resulting in an increase in residual jitter.

(Means for Solving the Problems) The present invention is a method for correcting time axis errors that occur during playback, in which part or all of the horizontal blanking interval of a recorded video signal is replaced with a synchronization signal. After that, a reference phase burst signal is inserted within the horizontal blanking period of the video FM signal obtained by frequency modulation and recorded on a recording medium, and when playing back, the reference phase burst signal is extracted and this reference phase burst signal is This method generates control pulses for correcting time axis errors.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1 and 4 are diagrams for explaining the case where the time axis error correction method according to the present invention is applied to a VTR that records and plays back MUSE signals, and FIGS. FIG. 2 is a diagram illustrating the characteristics when the method according to the present invention is applied to a general VTR that does not have a conventional VTR.

In FIG. 1, the MUSE signal 2, which has a short horizontal blanking period (MUSE HD period) of about 700 nsec, is input to the synchronous replacement circuit 1, where the horizontal blanking period is replaced with a negative polarity 1/1 signal ( Signal ■). After this signal ■ is modulated by the FM modulation circuit 2 (
signal (■), part of the horizontal blanking period is replaced by the reference burst signal by the burst insertion circuit 3 (
Signal ■).

This signal (2) is recorded on a video tape by the magnetic head 4.

On the other hand, during reproduction, the F reproduced by the magnetic head 4
The M signal is demodulated by the FM demodulation circuit 5 (signal ■)
, the same gate detection circuit 6 detects the falling edge 7 of the negative polarity synchronization signal included in the demodulated signal (2). Furthermore, the burst gate generation circuit 8 generates a gate signal for extracting the reference burst signal present in the FM signal (signal 2).

Further, the window generating circuit 9 that receives the falling edge 7,
A reference phase signal ■(
Date signal to extract write start pulse)■
occurs. The signal ■ is supplied to the AND gate 10, and the reference burst signal in F M (i8 is extracted,
The S/N ratio is increased through a bandpass filter 11 and a waveform shaping circuit 12 (signal ■), and the signal is input to an AND gate 13 for extracting the signal ■.

FIG. 3 is a block diagram showing an example of a digital time axis error correction device.

This figure shows a device that receives the signals ■ and ■ explained in FIG. 1 and outputs a video signal after jitter correction.The components from the synchronization detection circuit 6 to the AND gate 13 in FIG. It is represented as a circuit 22.

In FIG. 3, the reference phase is detected by the reference phase detection circuit 22 every horizontal scanning period (IH) of the reproduced video signal (2), and the write clock is phase-synchronized with the reference phase before IH in the phase lock loop 23. A phase comparison is made with a phase reference signal (WCk8) obtained by frequency dividing (Wck) by eight, and the signal ■ is sampled by WCk via the A/D conversion circuit 24 and converted into a digital signal. and written into the memory 21.

The signal stored in the memory 21 is clocked by a stable clock (R
ck), is converted into the original analog video signal by the D/A conversion circuit 25 and the low-pass filter 26, and is output. Further, the write and read addresses of the memory 21 are set by a memory address counter 27 based on the reference phase signals ①, Wck, and RCk.

By the way, since the MUSEHD signal used in the MUSE method differs for each horizontal scanning period, in this example, instead of replacing the entire horizontal blanking period with a synchronization signal during recording, a part of the HD signal is replaced as shown in Fig. 5. HD marker 3 as shown
FIG. 4 shows a circuit configuration for restoring the MtJSEHD signal based on this F(D marker 30).

FIG. 4 shows the configuration between the memory 21 and the D/A conversion circuit 25. As shown in FIG.

A MUSE HD signal is stored in the ROM 31 in advance, and the HD signal of the digital signal read from the memory 21 is stored in advance.
The period data is configured to be replaced with data from the ROM 31 in response to the HD marker 30. That is,
The HD marker level detection circuit 32 detects the HD marker 30 from the read data 0 (the content is [phase]') from the memory 21, generates a marker detection signal ■, and outputs the signal 0.
During the period in which is being generated (HD period - HD marker period), the data @ from the ROM 31 is
3 to the D/A conversion circuit 25 manually. As a result, the D/A conversion circuit 25 outputs MUSE
The HD signal is restored and becomes the original MUSE signal.

Next, Figure 6 (aj, (bl) and Figure 7 (al, (
The time axis error correction method according to the present invention is
A case where the present invention is applied to a VTR other than a USE signal VTR will be explained.

In the conventional method, FM modulation 4 is performed after burst addition 40.
1 and returns to FM via the tape head system 42, which is the FM transmission path. A43 has been done. The synchronization signal and burst extraction are performed after FM demodulation. On the other hand, in the method of the present invention, a burst is inserted after FM modulation 41, and FM demodulation 41
The difference is that a burst is extracted before 3.

Therefore, the frequency spectrum of the burst signal after FM modulation in the conventional method becomes the O mark in FIG. 7(b). When the same signal is reproduced, it appears as shown in the figure (bl), and the burst signal after demodulation is subject to waveform distortion. On the other hand, in this method, a burst signal of a single frequency is inserted after FM modulation, so sidebands are not generated, and a single spectrum is generated as shown in Figure 7 far. will have the following.

Therefore, by applying this method, it is possible to prevent waveform distortion of the burst signal from occurring.

(Effects of the Invention) As described above, according to the present invention, when recording and reproducing a signal with an extremely narrow horizontal blanking period, such as a MUSE signal, the reference burst, which only takes 2 to 3 cycles in Haasband, is used as a video FM signal. So, set the burst frequency to 2
Since it can be obtained ~3 times higher, it can be increased to about 6 to 8 cycles. In addition, since the burst frequency is a high frequency, the one cycle period is shortened, and as a result, the detection accuracy is also improved. A correction device can be provided.Furthermore, waveform distortion caused by unbalance phenomena occurring in the head-tape system can be prevented.

[Brief explanation of drawings]

Fig. 1 is a block diagram when the time axis error correction method according to the present invention is applied to a VTR that handles MUSE signals, Fig. 2 is a timing diagram showing waveforms of each part in Fig. 1, and Fig. 3 is a digital type time diagram. A block diagram showing an example of an axis error correction system, Fig. 4 is a block diagram showing a processing system that restores the MIJSE HD signal based on the HD marker, and Fig. 5 is a timing diagram showing waveforms of each part in Fig. 4. , FIG. 6(a) is a block diagram explaining the present invention in detail, FIG. 6(b) is a block diagram explaining the conventional method, and FIG. 7(al is a burst diagram when using the method of the present invention. A diagram showing the frequency spectrum of the signal after FM demodulation (FIG. 7 fb) is a diagram showing the spectrum of the burst signal when the conventional method is used. ■...Synchronous replacement circuit 3...Burst insertion circuit 20...Time axis error correction device 21...Memory 2
2... Reference phase detection circuit 31... ROM32
...HD marker level detection circuit Figure 4 @Figure 5

Claims (1)

[Claims] 1) A method for correcting time axis errors that occur during playback, which is a method for replacing part or all of the horizontal blanking period of a recorded video signal with a synchronization signal and then frequency modulating the video FM signal. A reference phase burst signal is inserted and recorded on a recording medium within a horizontal blanking period, the reference phase burst signal is extracted during playback, and a time axis error correction control pulse is generated based on this reference phase burst signal. A time axis error correction method characterized by: