JPS6040754B2 - Jitter removal method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a video tape recorder (VTR) that does not provide a sufficient guard band between adjacent recording trajectories or does not provide a guard band at all in order to improve the utilization efficiency of the recording medium.
) provides a method for stably reproducing color television signals using recording and reproducing devices such as the following.

In recent years, small WTRs for home use are moving toward 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 band, and is weighted to the low frequency band of the 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 a frequency-modulated luminance signal with a relatively high frequency can be prevented by azimuth recording with an azimuth angle of ±6° to +7°. However, there is almost no azimuth effect for low-frequency carrier color signals, and this method cannot prevent adjacent interference. Therefore, a block diagram of one method for removing adjacent interference is shown in FIG. 1, and color signal phase relationship diagrams thereof are shown in FIGS. 2 and 3, and will be explained. In FIG. 1, a carrier color signal contained in an NTSC color television signal entering an input terminal 1 is separated by a bandpass 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 reduction filter 4, mixed with a frequency-modulated luminance signal, and recorded on a tape via a head 5.

At this time, as shown by solid lines in Figure 2 a and b, the phase of the color signal is 90% for each line on one track (Chi).
00 advance, 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. A continuous signal having a frequency of m (m: positive integer, 'H: line frequency, for example, m〆N=40〆H) is created by the AFC circuit 7 from the horizontal synchronizing signal 6 separated from the input signal.

This signal is the head cutting signal 8 and the 90o phase rotation circuit 9.
Therefore, in Chi, 900 phases are formed for each line, and 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.
．． A continuous signal A is obtained by converting the frequency of the signal from the 58MH2 oscillator 11 using the frequency converter 12. The phase inverter works only during playback and can be considered to be a simple bypass during recording. Since the phase of this continuous signal is 900 degrees leading for each line in Chi, and 90 degrees lagging for each line in Ch2, the signal frequency-converted to a low frequency band with this signal also has such a phase relationship. When reproducing a signal recorded with such a phase relationship, when reproducing Chi, the component shown by the broken line in Figure 2a as crosstalk from Ch2 will become Ch2.
During 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. When this signal is returned to its original frequency using the continuous signal A that has been processed in the same manner as during recording, the frequency converter 14, and the bandpass filter 15, the phase also returns to the original continuous state, and the main signal of Chi and Ch2 The components and crosstalk are shown by the solid and broken lines in FIG. 2c and d. The main signal component, which is the sum of this signal and the signal obtained by passing this signal through the one-line delay line 16, is doubled in the same phase, and the crosstalk component is canceled out in the opposite phase, resulting in a signal 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 restores the color signal phase to its original state and serves to remove the jitter that occurs during recording and reproduction.

The horizontal synchronization signal 6 during reproduction is the reproduction horizontal synchronization signal frequency 〆H'
A signal having a frequency m times m, that is, m〆H' is obtained.
This signal has the same frequency fluctuations as the reproduced signal. Also, the burst signal is separated from the reproduced output color signal at the output end 17 by the burst signal separator 18, and the phase is compared with the stable signal of the reference oscillator 19 of 3.58 Md' by the phase comparator 20, and the error signal is So 2. Controls the frequency and phase of the oscillator 1. When the low frequency conversion color signal is frequency-converted using a continuous signal A having the sum frequency of the output signal of the oscillator 11 and the output signal (frequency m〆w') of the phase inverter 10, the phase is restored to the original value, and the jitter is removed. - removed reference oscillator'9
A color signal whose phase is locked to / is obtained at the output terminal 17. In this recording/reproducing system, phase switching is performed between Chi and Ch2 as shown in FIG. 3a.

When the phase switching between Chi and Ch2 during reproduction is performed at exactly the same position as during recording, the phase between Chi and Ch2 of the output color signal is continuous as shown in FIG. 3b, and no problem occurs. 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 effective point of Chi and Ch2, so it will be shifted to the upper side of Figure 3c. The phase relationship is as shown, so the phase of the output color signal changes from the P, B signal A to the REC color signal (Figure 3a).
), as shown in the lower part of FIG. 3c), and a phase difference of 1800 is generated between Chl and Ch2. In such a case, the phase of the oscillator 11 is controlled by the output signal of the phase comparator 20 in FIG. 1, and the phase of the color signal of Ch2 is set to 00. However, the oscillator 11 is made of a stable element such as a crystal. Because it consists of
Since the phase difference of 1800° cannot be absorbed immediately, the color may not be stable until the middle of the screen. Circuits 21 and 10 are used to compensate for this. Reference numeral 21 denotes a circuit (ID circuit) for operating the phase inverter 10 when it is detected that a phase difference of 1800 degrees has occurred between the output of the phase comparator 20 and the output color signal.

That is, when the phase of the output color signal is reversed, the circuits 21 and 10 operate, and the phase of the signal A is reversed, so that the phase of the output color signal is reversed, 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 of frequency m 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, the oscillator 1 1 does not operate APC for several lines after the head opening until AFC stabilizes.
If it runs freely (field start inhibit), the oscillator 11 will not fluctuate during that time, and as a result, the color will become stable quickly. Further, the ID circuit also operates stably after the AFC is stabilized. However, even with this method, another disadvantage remains.

Although FIG. 3 shows the state in which the reproducing head switching position moves one line forward compared to recording, let us now consider the case in which it moves backward. FIG. 4 shows the case of moving three lines backward. As can be seen in Fig. 4, in such a case, the P, B signal A advances in phase by 900 for each line until the switching point between Chi and Ch2, and thereafter lags in phase by 900. Therefore, the phase of the output color signal is as shown in the upper part of Figure 4b), assuming that the REC color signal (Figure 4a)) is subtracted from the P, B signal A. As shown on the side, 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 ID 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, but if this is repeated many times, the phase of the oscillator 11 will deviate from the stable state. Accurate m output may not be obtained, and color output signals may not be stably obtained. The present invention attempts to compensate for this drawback and obtain 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 various parts in FIG. In FIG. 5, the same signals as in FIG. 1 represent the same things.

Head switching signal 8 when switching tracks during recording (Figure 6a)
), a delay device 22 such as a monostable multipipulator that operates on the rising edge and a delay device 23 that operates on the falling edge (each number of delay time lines) are used to generate the delay time shown in Fig. Sb.
and c, and drive the RS flip-flop 24 which is set at the falling edge of the output 22 (FIG. 6b) and reset at the falling edge of the output 23 (FIG. 6c), As shown in FIG. 6d, a signal delayed by several lines from the head switching signal 8 is obtained. The output signal d of the flip-flop 24 causes the 900
The phase rotation circuit 9 is controlled, and when this signal is at a high level, the continuous signal A has a phase advance of 90 degrees per line, and when this signal is at a low level, it has a phase delay of 90 degrees. In this way, the phase switching position between the tracks of the recorded color signal can be set several lines later than the head switching position. When reproducing a signal recorded in this way, the head switching signal 8 directly passes through the recording/reproducing switch 25, controls 9 and the phase rotation circuit 9, and generates a continuous signal in the same manner as in the case of FIG. A
is obtained, and a reproduced color signal is obtained at the terminal 17.

At this time, the m circuit and the field start inhibit operate as described above. In this way, even when recording with self-mirror reproduction and immediately reproducing, the phase relationship between the tracks of the recorded and reproduced color signals will be in the front during reproduction, as shown in Figure 3c. In addition, even if the following method results in the result as shown in Fig. 4, since the color signal phase rotation switching position between tracks during recording is set in advance several lines later than the head sliding position, as shown in Fig. 4. As shown in the figure, the color signal phase rotation effective position during reproduction is not later than that during recording, and the color signal can be reproduced stably by the m circuit and the field start inhibit. In FIG. 5, a method has been described in which the color signal phase rotation switching signal between tracks during recording is created using the delay circuits 22, 23 and the RS flip-flop 24 from the head switching signal, but any other method can be used as shown in FIG. You can also create a signal like this.

For example, it can also be obtained by driving a flip-flop whose polarity is controlled by the head switching signal using a vertical synchronization signal separated from the input signal. At this time, the color signal phase rotation switching position during recording depends on the timing of the vertical synchronization signal. By the way, the head switching position is usually 5 to 8 from the vertical synchronization signal.
It is set in front of the line, so 5 to 8 points from the head switching position.
A switching signal after the line can be obtained. In the above explanation, an example of the present invention has been 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 and C
In h2, an example is shown in which the reproducing position is three lines after the recording in the case of a method of reversing every line. 7th
As can be seen from the figure, in this method, the same phenomenon as in the method shown in Fig. 1 occurs before the head sliding door (the output color signal phase is the P, B signal A minus the REC color signal). .
), the present invention is effective. 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 Chi color signal phase is constant, and the Ch2 phase is delayed by 90o for each line, and during playback, the 1-line delay line 16 in Fig. 1 is replaced with There is a method using a two-line delay line. Figure 8 shows an example in which the playback switching position is three lines after the recording in this method (the output color signal phase is
It is obtained by subtracting the REC color signal from the P, B signal A. )
. In this case, m in the PAL system is a method of detecting 900 or 1800 discontinuities in the output color signal and shifting the phase of signal A by 900. The 900 discontinuities are absorbed by APC, and continuous signal A is only inverted. There are several ways to do this, but in any case, the phase of the oscillator 11 is adjusted so that the color signal is oo
It is undeniable that the phase will deviate from when it is stable. This degree is greater than in the case of NTSC, where the ID operates with only a change of 00, 1800. Therefore,
Since m after the head transition becomes more unstable, it is very effective to set the rotary transition position of the color signal phase at the time of recording later than that at the time of reproduction as in the present invention. P.A.
Even when using the L method, where the Chi color signal phase is constant, Ch2 is inverted every two lines, and adjacent interference is removed using a two-line delay line, the result will be exactly the same as in Figure 7 if two lines are considered one block. The invention is valid.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional jitter removal method, FIGS. 2, 3, and 4 are explanatory diagrams of the same operation, and FIG. 5 is a block diagram showing one embodiment of the present invention. 6 are explanatory diagrams of the same operation, and FIGS. 7 and 8 are diagrams illustrating the operation of other embodiments of the present invention. 1...Input terminal, 2, 15...Band filter, 3, 12, 14...
...Frequency converter, 4,13...Low pass filter, 5...Head, 7...DFC circuit,
9...90o phase rotation circuit, 10...phase inverter, 11...oscillator, 16,22,23...delay circuit,
18... Burst gate circuit, 19...
・Fixed oscillator, 20... Phase comparator, 24...
...flip flop. Figure 1 Figure 4 Figure 2 Figure 3 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1 The color signal in the color television signal to be recorded is
The frequency is converted to a low frequency band, and the phase of the color signal recorded on the recording track is changed every n lines (n: a positive integer) and recorded on at least one of the adjacent recording tracks. The low-pass conversion color signal has the sum frequency of the output signal of the oscillator whose frequency and phase are controlled by the output of the phase comparison of the reference oscillator signal and the burst signal in the output color signal, and the continuous signal synchronized with the horizontal synchronization signal. In a method that converts the frequency of a continuous signal to the original frequency and phase to remove jitter in the reproduced color signal, the phase switching position of the color signal between tracks during recording is later than that during playback. A jitter removal method characterized by setting the settings as follows.