JPS6015196B2 - Time axis error correction method - Google Patents

Description

[Detailed Description of the Invention] The present invention solves the problem of time axis error (jitter) in video recorders.
More specifically, the present invention relates to a highly accurate jitter correction method in a SECAM video recorder.

Conventionally, for jitter correction in a SECAM system VTR, jitter correction was performed for each horizontal line by comparing the synchronization signal portion of the reproduced video signal with a reference synchronization signal. In this method, there is a limit to the time axis precision of both horizontal synchronization signals being compared, and the jitter after correction is approximately 30 nanoseconds P-P.
That's about it. The present invention eliminates such residual jitter by PAL,
The object of the present invention is to obtain a jitter correction method that achieves a P-P of about 1 nanosecond, which is comparable to that of an NTSC VTR. Generally NTSC
In this type of VTR, coarse jitter correction (AFC) is first performed between the horizontal synchronization signal of the reproduced composite color video signal and the reference horizontal synchronization signal, and then the jitter-containing burst signal and the reference burst signal are Jitter is more precisely corrected (APC) by detecting the phase error between the two.

However, in the SECAM method, the NTS
Since there is no C signal color burst, it is necessary to insert a burst-like pilot signal into the SECAM composite color video signal during recording. In this case, the pilot signal needs to have better time axis accuracy than the horizontal synchronization signal, and the problem is where to insert it in the SECAM composite color video signal to be recorded. The present invention is a SECA that records such burst-like pilot signals.
M composite color video signal, which is inserted at an appropriate location in the signal and used for jitter correction purposes during playback.

The figures show one embodiment of the present invention, with FIG. 1 being a block diagram of its configuration and FIG. 2 being an operational waveform diagram.

A composite color video signal to be recorded is input to terminal 1. FIG. 2a shows this signal waveform. In this example,
The 〇R line of this signal is 282 days (=4.4062 days)
8MHz), but the D
'8 line (272 days, 4.29 MHz) can also be used. Circuit 12 is an unmodulated subcarrier (〇R line, 4.40628MHZ) extraction gate pulse P
, and to create a burst gate extraction switcher pulse P2, including a synchronous separator 14 and a vertical synchronous separator 1.
6, horizontal sync separator 18, frame pulse separator 20,
It consists of a 4-field ID separator 22, a 1/2 minute separator 24, a burst insertion separator gate 26, and a monomulti T, -L.

Monomulti T and T2 determine the timing of T and T2 in FIG. A burst-like 282 deadline as shown in FIG. 2b is generated every two lines of the SECAM signal. This signal (FIG. 2b) cannot be used as it is as a sample pulse for the phase detector.

This is because the unmodulated subcarrier of the extracted SECAM signal itself has a phase sequence of 0, 0, and 0 that repeats every three horizontal lines. To overcome this problem, the signal at gate 50 is amplified by amplifier 28 and then doubled by counter 30. This makes the phase of each line constant. Therefore, from this double burst, 2
A continuous wave whose phase is sampled for each horizontal line can be created. Furthermore, in this case, there is no need to distinguish between 0, 0, and 0 lines of the SECAM signal, and by simply focusing on the 4-field lock phase of the video, it is possible to correctly extract continuous waves containing jitter. becomes. That is, jitter information can be extracted every two horizontal lines, and jitter velocity error components can also be extracted every two horizontal lines. On the other hand, a burst signal serving as a reference for jitter correction can be extracted from the input (reference) SECAM signal in exactly the same manner as described above. The doubled burst from counter 30 (2×282〆H=8.81250MHZ) is shown in Fig. 2c.
, which is applied to the phase detector 32.

Phase detector 32 and center frequency na = 8.8129MH
The voltage controlled oscillator 34 of FIG. 2 constitutes the start-stop oscillator of the AFC-APC oscillator and provides a continuous wave (FIG. 2d) in which the frequency and phase of the burst of FIG. 2C is reflected. This is amplified by an amplifier 36 and provided to a 1/2 frequency divider 38. The frequency divider 38 is 2×282 days (
= 8.81250 MHz) is cut in half so that it can be recorded on a VTR. The output of the 1/2 frequency divider 38 is shown in FIG.

The switcher 42 is given the above-mentioned gate pulse P2 as a strobe pulse. This pulse P2 is a continuous wave (
FIG. 2e) is strobed at the appropriate time so that it can be inserted as a pilot burst at the appropriate location in the original composite video signal. switchia 4
A burst strobed at 2 is shown in FIG. 2a, which is amplified in amplifier 44 and then combined with the input SECAM signal at terminal 10 (FIG. 2a) in mixer 46. The mixer output at terminal 48 is of the form shown in the waveform of FIG. 2g, containing the burst of FIG. given for a purpose. In the output waveform of FIG. 2g, the timings L and T4 inserted into the horizontal synchronous portion of the burst (FIG. 2f) power SECAM signal are the first
It is determined by the time constants of the two monomultis t and T4 in the figure. As described above, according to the present invention, jitter correction can be performed with higher accuracy without changing the SECAM signal recorded on the video recorder, and the SEC
By doubling the unmodulated subcarrier portion of the AM signal, the complexity of 0, 0, m line control can be avoided. Further, the SECAM signal that is the source before recording generally also includes a time axis error.

This occurs due to recording/reproduction and transmission conditions at the broadcasting station, or when, for example, a 1 hour and 2 minute program is to be broadcast in one hour. In this way, if the SECAM signal before recording already contains a time-base error, the unmodulated carrier included therein also contains the same amount of time-base error. According to the invention, therefore:
An unmodulated carrier containing the same time axis error as the video signal is used as a pilot signal, and after being passed through a VTR recording and reproducing string, it is compared with, for example, a reference oscillation output of a fixed frequency, and phase control is performed. Not only the time rut error caused by this, but also the time axis error that occurred before that can be corrected.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is an operational waveform diagram at various positions in FIG. In the figure, 26 is a non-modulated subcarrier extraction gate, 30
32 is a phase detector, -34 is an oscillator, and 42 is a burst gate switcher. Figure 1 Figure 2

Claims (1)

[Claims] 1 Extract the unmodulated carrier part of the SECAM composite color video signal every horizontal period, multiply it by 2, and
A time axis characterized in that the oscillator is controlled by the output of a phase comparison between the multiplied signal and the output of the AFC-APC oscillator, and the output of the oscillator is used for phase control for time axis error correction of the video signal. Error correction method.