JPS594918B2 - Recording and reproducing method of PAL color television signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recording and reproducing PAL color television signals.

When comparing the PAL color television system with the NTSC system, as shown in Figure 1, the phase of the color subcarrier for one color signal component, for example, the color difference signal (R-Y) signal 5, is one horizontal scan. 1800 per period
In contrast, the phase of the color subcarrier for the color difference signal (B-Y) signal is the common phase for each horizontal scan period.

Therefore, the color difference signal (R-Y) signal is characterized in that it is symmetrically inverted with respect to the phase of the 10 color subcarriers regarding the (B-Y) signal every horizontal synchronization. and (R
A burst signal is used to identify the phase of the color subcarrier for the (B-Y) signal, and the burst signal phase is, as shown in FIG.
Burst signal B+ (SBn) with phase advanced by 1350 and 1
The burst signal B-(SB(n+1)) delayed by 350 is transmitted alternately every horizontal period.Here, the horizontal scanning frequency fH of the PAL system is 15.625KH2, the vertical scanning frequency fv is 05OH2, and the color subcarrier frequency. fs is about 4.4
It is 3MH2. Generally speaking, when a color television signal is recorded and played back using a recording/playback device, time axis fluctuations (hereinafter referred to as "5"
(abbreviated as lower jitter) occurs.

This jitter appears in the luminance signal as shaking of the screen, and in the color signal, it causes phenomena such as color unevenness or no color at all. Therefore, even in simple recording/playback devices, it is customary to perform jitter correction in color signal processing. An automatic phase control circuit (APC) is normally used for this jitter correction circuit, and the phase pull range of this APC circuit is
n) is the maximum fH from the sampling definition 15.75KH
2 (NTSC) experimental value is 12-13 KHz. However, in the above-mentioned PAL5 color television signal, the burst phase differs by 900 relative to each line, so the theoretical maximum phase pull-in range of APC is 7 in fH/2.
．． The frequency is 8KHz, and the experimental value is 5 to 6K1Iz.
Here, in a simple recording/playback device, the frequency fluctuation due to jitter is about several kHz, so if there is a change in the center frequency of the variable frequency oscillator of the APC circuit, the APC similar to NTSC
When recording and reproducing PAL color television signals, circuits sometimes have problems such as color unevenness or no color at all.
In view of these points, the present invention proposes a recording and reproducing method that can obtain stable and normal hues in recording and reproducing PAL color television signals.

An embodiment of the present invention will be described below with reference to the drawings, taking a low frequency conversion recording and reproducing method as an example.

Here, the low-frequency conversion recording and reproducing method separates the luminance signal and carrier color signal from the PAL color television signal, and the luminance signal is subjected to angle modulation, such as frequency modulation, on the high frequency side (Fig. 3 Y-
FM), and the carrier color signal is converted to a lower frequency of about several hundred KHz (Cc in FIG. 3), and is recorded on a recording medium with a spectrum as shown in FIG. 3. When playing back, it becomes the spectrum shown in Figure 3. It is assumed that the switch circuit 7 alternately switches terminals A and b for each horizontal synchronizing signal. Therefore, the output of the switch circuit 7 becomes ≦≦2 in FIG. Ha is N
Similar to TSC, the burst phase is the same for all lines. This means that from equations (1) to (4), take B+ for line n and B-1 for line n+1,
σN,. n+2, n+
On the 4th line: *From the first line, a high-pass filter and a low-pass filter separate the frequency modulated wave and the low-pass converted carrier color signal.

The frequency modulated wave is frequency demodulated and becomes a luminance signal output. On the other hand, the low frequency converted carrier color signal is frequency converted and jitter corrected to become a carrier color signal output. Now, reproduction carrier color signal processing related to the present invention will be explained with reference to a block diagram. FIG. 4 is a basic block diagram including the APC circuit of the present invention. A signal reproduced from a video head (FIG. 3) is connected to an input terminal 1, and a low-pass filter 2 separates a low-pass converted carrier color signal Cc. This frequency is Fc. This low frequency converted carrier color signal Cc is sent to the first frequency converter 3.
This first frequency converter outputs a bandpass filter 16, which will be described later. Frequency conversion is performed with a carrier wave having a frequency of FO+F8 to create 2f0+F8, F8, and a carrier color signal (frequency F8) is obtained by a bandpass filter 4, which is connected to a carrier color signal output terminal 5. The burst phase of this carrier color signal output is the phase shown in FIG. 5A from FIG. This can be expressed numerically as follows.

This carrier color signal A is directly connected to the a terminal of the switch circuit 7, and is passed through the phase shifter 6 of the switch circuit 7
Connect to the terminal. The burst phase of the b terminal is as shown in Figure 5. In this case, the 90 phase shifters 6 are shown with a 900 lag phase (the present invention can also be achieved with a 900 lag phase). Expressing this numerically, the burst phase difference for each line is 1800 from equations (6) and (7).

In this way, in the case of FIG.
There is no problem with the circuit, but in the case of Figure 5 2, one line per line.
There is a phase difference of 80 degrees, and the synchronization pull-in range of a normal APC circuit is 7.8 KHz in FH/2. The present invention is based on NTS
The synchronization pull-in range is the same as in C. Next, the main parts of the present invention will be explained in detail.

The output of the switch circuit T shown in FIG. 4 is doubled by a doubling circuit 8. Since the carrier chrominance signal is a signal with a band, it is difficult to simultaneously transmit the phase and amplitude of the actual chrominance signal portion, but this is not a problem because only bursts are caused by the present invention. A burst gate circuit 9 extracts a burst from the output of the doubler 8 and connects it to a phase comparator 10.

The phase comparator 10 detects the 2fs frequency burst and F
A reference fixed frequency oscillator 11 with a frequency of s is passed through a phase shifter 12, and the phase is compared with a reference signal of a 2fs frequency which is doubled by a doubler circuit 13, and the error signal is used to control the variable frequency oscillator 1.
Control 4. The variable frequency oscillator 14 is, for example, 2fc (
(low-pass conversion carrier color signal frequency). The frequency of this variable frequency oscillator 14 is divided by two by a frequency divider 11, and the output of the frequency divider 2 circuit IT and the reference fixed frequency oscillator 11 are transferred to a second frequency converter 1.
5, the band pass filter 16 converts the frequency to Fc
+Fs and connect it to the first frequency converter. Then the fourth
8 to 16 in the figure will be explained together with mathematical formulas.

For convenience of explanation, the phase of the doubler circuit 8 is assumed to be ψ,=o.

Moreover, for C, if we change the phase to a phase 135 degrees ahead of the B-Y axis, the burst phase of C can be determined from equation (5), and for 2, if we change the phase to a phase 135 degrees behind the B-Y axis, we get: According to equations (7) and (6), the output of the doubler circuit 8 is from equation (8), from equation (9), from the QE equation. Since there is continuity of phase in each case, the result is shown in Fig. 5 (E).

As for the second one, they are in the same phase according to the formula A2xl3). This is because a phase difference of 180 becomes a phase difference of 3600 by doubling, but 360° means that the phase is compared at the same position in the APC circuit, and the phase difference is equivalent to 00. Therefore, the burst phase of the output of the burst gate circuit 9 has continuity for each line. If the output of the doubler circuit 13 from the constant fixed frequency oscillator 11 is also set to Sin2ωSt, there is no error, and the output of the variable frequency oscillator 14 becomes Sin2ωCt. When this output is frequency-divided by 2 and frequency-converted using this Sin(t)Ct and SinωSt of the reference fixed frequency oscillator 11, when the second term on the right side is extracted by the band-pass filter 16, COs
(ωs+ωc)t, and its frequency becomes Fs+Fc. As described above, according to the present invention, the synchronization pull-in range can be expanded by making the burst signals, which have relatively different phases by 900 lines for each line of a PAL color television signal, continuous (same phase) for each line.

Moreover, in conventional simple recording/playback devices, the APC time constant cannot be made large due to the large amount of jitter, and furthermore, since the L-C type is used as the variable frequency oscillator, the error signal has a 7.
There have been problems such as the 8 KHz rectangular wave signal becoming dull and hue unevenness occurring within the line, but these problems can be solved by the present invention. Furthermore, a horizontal synchronization signal is used as the control signal for switching the switch circuit 7 in Fig. 4, but if the horizontal synchronization signal increases or decreases due to dropout,
To make the present invention more effective, the buffer oscillator is controlled by a horizontal synchronizing signal, and the switch circuit 7 is switched by the buffer oscillator output, thereby ensuring reliable switching.
If there is a large amount of jitter (large frequency fluctuation) in a simple recording/playback device, it is often not possible to keep up with the APC circuit alone, so an automatic frequency control circuit (hereinafter abbreviated as AFC) is added. A block diagram for making the present invention effective is shown in FIG.

The same numbers as in FIG. 4 indicate the same circuits. Reference numeral 1 denotes an input terminal for a reproduced RF signal, 2 a low-pass filter that extracts a low-pass converted carrier color signal, and a first frequency converter 3 that outputs an F from the band-pass filter 16.

Frequency conversion is performed using a carrier wave having a frequency of +F8, Fs is extracted by a bandpass filter 4, and connected to a carrier color signal output terminal 5. The carrier color signal output is directly connected to the (a) terminal of the switch circuit 7 and via the 900 phase shifter 6 to the switch circuit 7.
Connect to terminal (b) of This switch circuit 7 output is 2
A burst is obtained by a burst gate circuit 9 through a multiplier circuit 8 and connected to a phase comparator 10. The phase comparator 10 compares the phase of the burst with a signal obtained by doubling the output of the reference fixed frequency oscillator 11 in a doubling circuit 13 (the phase shifter in FIG. 4 12 is omitted because it may or may not be provided). , and controls the variable frequency oscillator 18 with the error signal. The frequency of this variable frequency oscillator 18 is the low conversion frequency F. AFC and APC
It is now divided into 2f1. The 2 frequency divider circuit 19
Divide 1 by 2 to obtain f1.

On the other hand, the AFC section receives the reproduction horizontal synchronization signal from the reproduction horizontal synchronization signal input terminal 20;
The phase comparator 23 compares the phase with a signal obtained by dividing the oscillation frequency F2 by n by the n frequency dividing circuit 22, and controls the variable frequency oscillator 21 using this error signal. At this time, the ratio of frequencies f1 and F2 is selected to be F2>f1. This means that most of the frequency fluctuations are covered by AFC and the rest by APC. However, the frequency converter 24 divides the frequency by 2 into the frequency divider 1.
9 output F and the variable frequency oscillator 21 output F2 are subjected to frequency conversion, and the band pass filter 25 obtains f1+F2. Here, f1 and F2 are selected so that f1+F2-FC. Then, the frequency converter 26 generates the reference fixed frequency oscillator 11.
Output Fs and bandpass filter 25 output F. F by a bandpass filter 16. +F, is extracted and used as the carrier wave of the frequency converter 3. Let us show an example of the setting values of f1 and F2.

For example, if the frequency division ratio of the AFC circuit (n in Figure 5 22) is N
If 3O, F2-FHX3O=15.625X30
=468.75KHz. fc is the standard recommended by EIAJ and is Fc-685.574KHz, so f1-FO
-F2-216.824KHz. That is, the APC is responsible for about 30% of the jitter, and the AFC is responsible for about 70%. Taking into account residual errors in APC, and performing compatibility and damping, the ratio of AFC to APC is approximately 2:1.
is good both experimentally and theoretically. If the present invention is applied to the system shown in Fig. 6, for example, assuming that the frequency fluctuation (jitter) is 2%, the result will be 685.574 x 0.02-14K.
The frequency fluctuation is Hz, and the jitter response of the APC is about 30% of that, so it is several kHz.

With the present invention, APC has the same synchronous pull-in range as NTSC, theoretical value FH, experimental value 12 to 13 KHz, and AP
Even considering the center frequency drift of the C variable frequency oscillator (FIG. 4 14, FIG. 6 18), it is well within the synchronous pull-in range, and the conventional problems can be solved. Here, the variable frequency oscillators 14, 18 and the frequency divider circuit 19 of the APC shown in FIGS. 4 and 6 have a structure in which the frequency of the frequency oscillator is divided by one for convenience of explanation. For example, if there is a frequency fluctuation of Δf in Fig. 4A, the APC phase comparator output will be an output of 2Δf, and the variable frequency oscillator output will be 2f1-2Δf, which is 2Δf.
The frequency divided output becomes F, -1t. Therefore, frequency fluctuations can be canceled out. Therefore, 14, 17, 18, 1 in Figures 4 and 6
9 may have any configuration as long as it has an equivalent operating principle. FIG. 7 shows another configuration example that provides the same effects as the present invention.

This is a modification of portions 5 to 10 of FIGS. 4 and 6. Figure 7 5
6 is a carrier color signal output terminal, 6 is a 90-channel phaser, 7 is a changeover switch 27 for switching between (a) and (b) terminals for each line, and the burst gate circuit 27 output is either C or 2 in FIG. It has a burst phase. This burst signal controls the ringing oscillator 28. The ringing oscillator 28 generates a continuous signal phase-locked to the burst phase. This ringing oscillator 28 output is
The multiplier circuit 29 doubles the signal, and the burst gate circuit 30 again obtains a signal equivalent to the burst signal from the double-multiplied continuous signal, which is then input to the phase comparator 10 similar to that shown in FIG. The characteristic of FIG. 7 is that the signal is multiplied not as an intermittent signal but as a continuous signal, so there is little phase change. Also, in the second burst gate circuit 30, 18
It is characterized by being able to reliably extract the transient response of the doubler circuit 29 when there is a zero phase difference. As described above, according to the present invention, even when there are frequency fluctuations in the recording and playback of PAL color television signals, the synchronization range of the APC circuit is expanded, the synchronization range is made as stable as in NTSC, and hue unevenness within the line is prevented. , , it is possible to provide a new method that does not cause problems with deviations in the center frequency of the variable frequency oscillator.

[Brief explanation of the drawing]

Figure 1 shows the PAL color television signal (R-
FIG. 2 is a phase diagram of the burst signal, FIG. 3 is a spectrum diagram of the low frequency conversion recording/reproducing method, and FIG. 4 is a phase diagram of the phase diagram of Y) and (BY). 5 is a waveform diagram thereof, FIG. 6 is a block diagram showing another embodiment, and FIG. 7 is a block diagram showing still another embodiment. 2...Low pass filter, 3...1st
frequency converter, 4...bandpass filter, 6
...90 phase converter, 7... switch circuit,
8...2 multiplier circuit, 9...burst gate circuit, 10...phase comparator, 11...
...Reference fixed frequency oscillator, 13...2 multiplier circuit, 14...Variable frequency oscillator, 15...
second frequency converter, 16... bandpass filter,
17...2 frequency divider circuit.

Claims (1)

[Claims] 1 The luminance signal of the PAL color television signal is angularly modulated on the high frequency side, the carrier color signal is converted to the low frequency side, and recorded as a low frequency converted carrier color signal, and during playback, the angle modulated wave is demodulated. In this recording/reproducing method, the phase of the carrier color signal is alternately changed to 0° or 90° in each horizontal scanning period. The signal is doubled to obtain a color burst signal with a frequency of 2f_s, the phase of this color burst signal is compared with a reference signal with a frequency of 2f_s associated with a reference oscillator, and this phase error signal is used to control a variable frequency oscillator, A method for recording and reproducing a PAL color television signal, which converts at least the frequency of an oscillator output and the frequency of the reference oscillator output, and uses the frequency-converted signal as the signal for heterodyning.