JPS6038072B2 - Jitter removal method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In order to improve the utilization efficiency of recording media, the present invention provides a video tape recorder (VT) that does not provide a sufficient guard band between adjacent tape tracks or does not provide a guard band at all.
The present invention provides a method for stably reproducing color television signals using a recording/reproducing apparatus such as R).

In recent years, small WTRs for home use are moving towards high-density recording, and the majority are two-head helical scan type and guard bandless recording.

To record a color television signal with such a VTR, the luminance signal is frequency modulated, the carrier color signal is converted to a low frequency signal, and is recorded while being superimposed on the low frequency frequency modulated luminance signal. In order to prevent interference with adjacent signals due to guard bandless recording, a method of changing the direction of the head gap in adjacent tracks (azimuth recording) is being explored. Since the azimuth loss is large as the azimuth angle is large and the recording wavelength is short, adjacent interference of the frequency-modulated azimuth signal having a relatively high frequency can be prevented by azimuth recording with an azimuth angle of 6o to 70. However, there is almost no azimuth effect with respect to the low frequency carrier color signal converted to the low frequency band, and this method cannot prevent adjacent interference. Therefore, a block diagram of one method for removing adjacent interference is shown, and FIGS. 2 and 3 show phase diagrams of color signals and will be explained. In FIG. 1, a carrier color signal is separated from an NTSC color television signal inputted to an input terminal 1 by a filter filter 2, and in the presence of a continuous signal A, a frequency converter 3
The signal is converted to a low frequency signal by a low-pass filter 4, mixed with a frequency-modulated luminance signal, and recorded on tape through a head 5.

At this time, the phase of the color signal is 90% for each line in one track chi, as shown by the solid lines in Figure 2 a and b.
The data is advanced by 0, and in the other track ch2, it is delayed by 90o for each line. Such a phase relationship can be achieved by creating a continuous signal A as described below. AF from the horizontal synchronization signal 6 separated from the input color television signal
The C circuit 7 generates a continuous signal with a frequency of m (m: positive integer, n: line frequency, for example, m (H) = 40 "H").

This signal is the head switching signal 8 and the 90o phase rotation circuit 9.
Therefore, in chi, the phase advances by 900 for each line, c
In h2, the phase is delayed by 90 degrees for each line. 3 locked to this signal and the free-running or burst signal of the input signal.
．． 58MH2 oscillator 1 1 signal to frequency converter 12
Continuous signal A is obtained by frequency conversion. Phase inverter 1
0 can be thought of as working only during playback and simply bypassing during recording. Since the phase of this continuous signal A is 90o phase-advanced for each line in chi, and 900o phase-lag for each line in ch2, the signal frequency-converted to a low frequency band with this signal also has such a phase relationship. When a signal recorded with such a phase relationship is reproduced, when chi is reproduced, the component shown by the broken line in Figure 2a as crosstalk from ch2 becomes c
During h2 reproduction, a component as shown by the broken line in FIG. 2b as crosstalk from chi appears in the output of the low-pass filter 13 together with the main component shown by the solid line.

This signal is converted into a continuous signal A, which is processed by the same machine as during recording.
When the frequency converter 14 and Obishiro filter 16 return to the original frequency, the phase also returns to the original continuous state, and chi, c
The main component of h2 and crosstalk are shown by the solid and broken lines in FIG. 2c and d. When this signal is summed with the signal obtained by passing this signal through the one-line delay line 16, the main signal component is doubled in the same phase, and the crosstalk component is canceled out in the opposite phase and is obtained at the output terminal 17. During reproduction, the continuous signal A is created in the same manner as during recording, and by frequency converting the color signal with this signal, it functions to restore the color signal phase to its original state and to remove jitter that occurs during recording and reproduction.

The horizontal synchronization signal 6 during playback is obtained from the playback signal, and therefore A
At the output of the FC circuit 7, a signal having a frequency of m times the reproduction horizontal synchronizing signal frequency na1' is obtained. This signal has the same frequency fluctuation as the reproduced color signal. Further, a burst signal is separated from the reproduced output color signal 17 by a burst signal separator 18; 3. 3. Compare the phase with the stable reference oscillator 19 signal of MHz using the phase comparator 20, and use the error signal as 3.
58MH2 oscillator 1 Controls the frequency and phase of 1. When the low frequency conversion color signal is frequency-converted using a continuous signal A having a sum frequency of the output signal of the oscillator 11 and the output signal (frequency m〆H') of the phase inverter 10, the phase is restored to the original value and the jitter is removed. - is removed, resulting in a color signal 17 phase-locked to the reference oscillator 19. In this recording and reproducing method, c
Phase switching is performed between hi and ch2 as shown in FIG. 3a.

If the phase switching between chi and ch2 during playback is performed at exactly the same level as during recording, the phase between chi and ch2 of the output color signal will be continuous as shown in Figure 3b, and no problem will occur. . However, as shown in Figure 3c, for example, chi and ch
If the switching position of 2 is shifted by one line between recording and playback, the signal A during playback will be delayed by 900 lines per line from the switching point of chi and ch2, as shown in the upper part of Figure 3c. Therefore, the phase of the output color signal is as shown in P.c of FIG. 3. Since the REC color signal (Fig. 3a) is subtracted from the B signal A, it becomes as shown in the lower part of Fig. 3c, and a phase difference of 1800 is generated between chi and ch2. In such a case, the phase comparator 20 in FIG.
The phase of the oscillator 11 is controlled by the output signal of ch2
The oscillator 11 works to set the color signal phase to 00, but since the oscillator 11 is composed of a stable element like a crystal, tracking is slow and it cannot absorb the 180° phase difference immediately. Colors may not be as stable as possible. Circuits 21 and 10 are used to compensate for this. When 21 detects that the output of 20 has a phase difference of 1800 in the output color signal,
This is a circuit for operating the phase inverter 10.

That is, when the phase of the output color signal is inverted, the circuits 21 and 10 operate to invert the phase of the signal A, so that the phase of the output color signal is inverted, and a signal of oo phase is obtained. In this way, stable color signals can be obtained. There is another problem with this method.

A continuous signal with a frequency m days is obtained at the output of the AFC circuit 7. During playback, especially during compatibility, a discontinuity in the horizontal synchronization signal called skew variation occurs when the head is shifted. This skew fluctuation causes the AFC output signal frequency to fluctuate, and it takes several lines until it stabilizes. Since the AFC output signal frequency is incorrect during this period, this error is attempted to be corrected by controlling the oscillator 11 with the output of the phase comparator 20, but since such APC has a slower response than AFC, If the frequency of the oscillator 11 changes without sufficient tracking or after some degree of tracking, it will take time for the APC to return to its original state after the AFC has stabilized, and it will take more time for the APC to become stable. Therefore, if the oscillator 11 is allowed to run free for several lines after the head is switched until the AFC is stabilized without activating the APC, the oscillator 11 will not fluctuate during that darkness, and as a result, the color will stabilize quickly. In addition, the (2) circuit also operates stably after the AFC is stabilized. However, even with this method, another disadvantage remains.

Although FIG. 3 shows the situation when the playback head position is moved one line earlier than the recording position, let us now consider the case where it is moved backward. FIG. 4 shows the case where the line is moved backward.
As can be seen in FIG. 4, in such a case, P. The phase of the B signal A advances by 900 for each line up to the switching point between chi and ch2, and thereafter the phase lags by 90o, resulting in a phase as shown in the upper part of Figure 4b. Therefore, the phase of the output color signal is , P. REC color signal from B signal A (Figure 4a)
As shown in the lower part of FIG. 4b, the output color signal is inverted even before the reproduction is switched. At this time, the m circuit operates, but since the phase of the output color signal is inverted for each line, once the m circuit operates and inverts the phase of the color signal, the color signal phase will be reversed again in the next line. The ID circuit works again. This is repeated until the head is switched.
If this is repeated many times, the phase of the oscillator 11 will deviate from the stable state, and when the first phase comparison is performed with several lines inhibited after head switching, it will no longer be possible to obtain an accurate m output, and the color output signal will be may not be able to be obtained stably.
The present invention attempts to compensate for this drawback and obtain a more stable color signal output.

Figure 5 is a block diagram of an embodiment of the present invention (reproduction system only)
will be explained by showing waveform diagrams of each part in FIG. Recording system is the first
As in the figures, the same symbols in FIG. 5 as in FIG. 1 represent the same things. During reproduction, signals as shown in FIG. 6 b and c are obtained from the head switching signal 8 (FIG. 6 a) by delay devices 22 and 23 such as monostable multipipulators that operate at falling and rising edges. The RS flip-flop 24, which is set at the fall of the output of 23 and reset at the fall of the output of 23, is driven to obtain gate signals for several lines before and after the head switching position, as shown in FIG. 6d. This signal d controls the gate circuit 25 to cut off the burst signal to the phase comparator 20 for a period of several lines before and after head switching (FIG. 6e). In this way, the oscillator 11 oscillates at a high speed for several lines before and after the head is activated, and during this period, it is not affected by the change in the color signal phase caused by the change in the switching register during recording and playback, and the previous stable state is maintained. Retain state. Therefore,
When the first burst signal arrives after head switching, the ID circuit also operates stably, and a stable color signal output can be obtained. In the above explanation, the burst signal is blocked by signal d,
Although the oscillator 11 is made self-running, it may be made free-running by any other method, and various modifications of the means for generating the signal e are conceivable. In the following explanation, an example of the present invention is described for the system shown in FIG. 1, but it is also effective for other systems.

Figure 7 shows that the phase of the color signal to be recorded is constant for chi,
2 shows an example in which the reproducing switching position is three lines after the recording in the case of a method of inverting every line. 7th
As can be seen from the figure, in this method as well, a phenomenon similar to that of the method shown in FIG. 1 occurs in front of the head sliding door, that is, the phase of the output color signal is different from the phase shown in FIG. 7b. The present invention is effective because the output color signal shown in figure b is obtained by subtracting the REC color signal in figure a from the B color signal A. Although the above description has been made regarding the case of the NTSC system, the present invention is also effective in the case of the PAL system.

As a method for removing adjacent color signal interference in the PAL system, the recorded color signal phase of CH is constant, and the phase of CH2 is delayed by 900 for each line, and during playback, the 1-line delay line 16 in Fig. 1 is replaced. There is a method using a two-line delay line. In this method, the phase of the output color signal is as follows:
P in FIG. 8b. This is obtained by subtracting the REC color signal in a of the figure from the B signal A, as shown in b of the figure. The ID in this case of the PAL system is to detect a 900 or 1800 discontinuity in the output color signal and shift the phase of the signal A by 900.The 90o discontinuity is absorbed by the APC, and the continuous signal A is only inverted. There are various ways to do this, but in either case, it is undeniable that the phase of the oscillator 11 deviates from the time when the color signal is stable at the 00 phase before the head opening. This degree is NT
Compared to the case of SC where the ID is working with only a change of oo, 1800, this becomes a larger one. Therefore, the ID after head switching becomes more unstable, and it is very effective to make the oscillator 11 free-running for several lines before and after head switching as in the present invention. In the PAL system, the chi color signal phase is constant, and the ch2 color signal phase is inverted every two lines. Even when removing adjacent interference with a two-line delay line, two lines are
If considered as a block, it becomes exactly the same as shown in FIG. 7, and the present invention is effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional recording method, FIGS. 2, 3, and 4 are explanatory diagrams of the same operation, FIG. 5 is a block diagram showing an embodiment of the present invention, and FIG. 6 is a block diagram showing the same operation. Operation explanatory diagram, 7th
8 and 8 are operation explanatory diagrams for explaining another embodiment of the present invention. 1...Input terminal, 2...Band filter, 3, 12, 14.
...Frequency converter, 4, 13, 15... ...
Low-pass filter, 6...Magnetic head, 7...AFC
Circuit, 9...9 phase rotation circuit, 10...
Phase inverter, 11...Oscillator, 16...Delay circuit, 18...Burst gate, 19...
... Reference oscillator, 20 ... Phase comparator, 22
, 23...Delay circuit, 24...Flip-flop, 25...Gate circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1 Convert the frequency of the color signal in the color television signal to be recorded to a lower frequency band, and convert the phase of the color signal recorded on at least one of the mutually adjacent recording tracks to n lines (n is an integer). During playback, the frequency and phase of the reproduced low-frequency conversion color signal are determined by comparing the continuous signal synchronized with the horizontal synchronization signal, the reference oscillator signal, and the burst signal in the output color signal. In this method, a continuous signal having the sum frequency of the output signal of the controlled oscillator is converted to the original frequency and phase to remove jitter in the reproduced color signal. A jitter removal method characterized in that the oscillator is left in a free-running state for a period of time.