JPS61161095A - Transmission system for pal type carrier chrominance signals - Google Patents

Abstract

PURPOSE:To prevent deterioration in picture quality such as bleeding by outputting carrier chrominance signals to be sampled every period of tau1/2 alter nately and outputting the resulting time-divided multiplexed signals as carrier chrominance signals for the current line. CONSTITUTION:Carrier chrominance signals separated by a Y/C separation circuit 2 from the input PAL system color video signals are supplied to a switching circuit 7. The circuit 7 is turned on for a period TAU2 corresponding to the high level of a symmetrical rectangular output wave fS of a 1/4 frequency divider 6 for outputting the input carrier chrominance signal, and turned off for the period tau1-tau2 corresponding to its low level, so as to inhibit signal transmission. Consequently, the carrier chrominance signals are gate outputted at a BPF8 as sampled signals during the periods tau1 for each period tau2. After passage through the BPF8, the carrier chrominance signals to be sampled are supplied to a record signal processing circuit 9 and thereby frequency converted into a low range. They are then frequency divided and multiplexed to frequency signals to be modulated obtained by frequency modulation of the carrier waves by brightness signals taken out from the circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a PAL carrier chrominance signal transmission system, and is particularly applicable to a PAL carrier chrominance signal transmission system with a limited band such as a VTR, which has a wider band than the transmission band. The present invention relates to a transmission method for transmitting a carrier color signal.

Conventional technology and problems Video signal recording and reproducing devices, especially home VTRs,
Due to the demand for lower prices and smaller size, the mechanical and electrical systems are simpler than those of broadcast VTRs, so the relative linear velocity between the tape and the head is lower, and the entire color video signal is frequency-modulated and recorded. , does not have a sufficient transmission band for playback, and has large time axis fluctuations. For this reason, most of the current home VTRs separate the standard color video signal into a luminance signal and a carrier color signal, and use the luminance signal to frequency modulate (FM) the low frequency carrier wave, as shown in Figure 5 (■). A frequency-modulated luminance signal with a frequency spectrum as shown in Figure 5 is used, and the carrier color signal is frequency-converted to a low frequency range to make it less susceptible to reproduction time axis fluctuations. A low-frequency conversion recording/playback method is adopted in which both signals are frequency-division multiplexed and recorded on a magnetic tape as carrier color signals, and during playback, the signal processing operation is performed in the opposite manner to that during recording to obtain a playback color video signal. It is well known that

However, in order to prevent interference between the luminance signal and the carrier chrominance signal, this method cannot widen the band of the carrier chrominance signal sufficiently; for example, the band of the baseband is only about 300kHz, so This caused deterioration in image quality such as color bleeding.

Therefore, the present invention samples a carrier color signal of the PAL system at a period τl that satisfies a predetermined inequality and sends it to a transmission line, and generates a sampled carrier color signal that has passed through the transmission line with a delay time of two horizontal scanning periods. It is an object of the present invention to provide a transmission system for a PAL carrier color signal that solves the above-mentioned problems by alternately switching and outputting two types of sampled carrier color signals having .tau.1/2.

Means for Solving the Problems The present invention provides a PAL carrier color signal having a band of rsc±'C (where fsc is the color subcarrier frequency).
A gate is output only during a fixed period τ2 for each cycle τ tube, and a sampled carrier color signal is transmitted in which sampling points on two adjacent lines are shifted from each other by τ1/4 in the horizontal scanning direction. do. here,
The above τl and τ2 are selected to values that satisfy the following inequality.

The transmitted sampled carrier color signal is on the current line and 2
After the two types of sampled conveyance color signals of the line before the horizontal scanning period are made, they are alternately switched and output every blind/2 period.

On the other side of the above-mentioned sampled carrier color signal that is transmitted, if the two-wave sampled carrier color signals of the current line and the line two horizontal scanning periods earlier are alternately switched and output every τ+/2, the result is obtained. The division multiplexed signal becomes a carrier color signal sampled at a sampling frequency substantially twice the sampling frequency fs (=1/τ1) in the transmission system (recording system). Therefore, fSC±(1/2
) Even if the transmission line can only transmit signals in the rs band,
A PAL carrier color signal of a band fsc±[C, which is wider than the transmission band, can be obtained by the receiving system (reproducing system). An embodiment of the present invention will be described below with reference to the drawings.

Embodiment FIG. 1 shows a block system diagram of an embodiment of the system of the present invention. First, to explain the operation during recording, the PAL color video signal input to the terminal 1 is supplied to the Y/C separation circuit 2, and is passed through the switch circuit 3 connected to the terminal R side to the sync separation circuit 4. is supplied to A phase-locked loop (PLL) 5 is supplied with the horizontal synchronization signal taken out from the synchronization separation circuit 4, and is synchronized in phase with this horizontal synchronization signal at a horizontal scanning frequency "a frequency that is an odd multiple of H".
2n-1) - generates and outputs a symmetrical square wave of fH (where n is a natural number, for example, n=101).

This symmetrical square wave is fed to a 1/4 frequency divider 6, where 1
/4 divided by repetition frequency (2n-1)・b+/
4, which is a symmetrical square wave, is applied to the switch circuit 7 as a switching signal.

Here, if the repetition frequency of the output symmetrical square wave of the 1/4 frequency divider 6 is fs, and the period is τ+ (=1/fs), then the repetition frequency [S is an odd multiple of < b+/4 as described above. Therefore, the phase differs by 90°, that is, τ1/4 between the beginning and end of one horizontal scanning period (1H). That is, the phases of the output symmetrical square waves of the 1/4 frequency divider 6 are shifted by 1/4 in two adjacent lines.

On the other hand, the carrier color signal in the band fSC±rc is separated from the input PAL color video signal by the Y/C separation circuit 2 (where fSC is the color subcarrier frequency of 4.43 MH).
7, and fc is a frequency of, for example, about 500 kHz) is supplied to the switch circuit 7. Switch circuit 7 is 177
High-level period τ2 of the output symmetrical square wave of the 4-frequency divider 6
(Here, τ2=τ/2) is turned on to selectively output the input carrier color signal, and during the low level period τ1-τ2, it is turned off to prevent the input carrier color signal from passing. Therefore,
The input carrier color signal is gate-outputted to the bandpass filter 8 as a sampled signal (sampled carrier color signal) only during a period τ2 of each period τ1.

Here, the above period τi is 1/(2fc)<τ1<1/"
The value is selected to satisfy both the first inequality c, and the second inequality 17/fsc≦τ2<τ1. Therefore, in the above period, 1 is, for example, 4/201 of the horizontal scanning period.
Selected for twice the period.

In this case, the repetition frequency [S] of the symmetric square wave applied as a switching signal to the switch circuit 7 is 785.156 kHz, which is 201/4 times the horizontal scanning frequency of 15.625 kHz.

In this way, the sampled carrier signal taken out from the switch circuit 7 can be -2
, -1, k, and +1 lines have waveforms and phase relationships as shown in FIG. 2(A). As can be seen from FIG. 2(A), the sampled carrier color signal has a sampling frequency fs (=1/τI).
As mentioned above, < odd number multiple of fH/4 (in the above example, 201
・Since the sampling point (f+/4) is selected as
Two adjacent lines (signal portion of period τ2) are signals that are shifted from each other by τ1/4 in the horizontal scanning direction. Also,
As shown in FIG. 2A, this sampled carrier color signal is a burst wave with a duration τ21 and a period τ1, and is converted into a continuous wave by the bandpass filter 8.

As shown in FIG.
The frequency characteristics are selected such that the frequency component in the fsc+fs band becomes a P wave. The sampled carrier color signal that has passed through the bandpass filter 8 is supplied to the recording signal processing circuit 9, where it is frequency-converted to a low frequency band, and then the carrier wave is frequency-modulated with the luminance signal taken out from the Y/C separation circuit 2. The obtained frequency modulated wave signal is frequency division multiplexed.

A frequency division multiplexed signal having a frequency spectrum as shown in FIG. 5 taken out from the recording signal processing circuit 9 is supplied to the recording rotary head 11 through the recording amplifier 10, thereby forming a video track on the running magnetic tape 12a. recorded.

Here, in the recording signal processing circuit 9, when frequency-converting the sampled carrier color signal to a low frequency band, the sampled carrier color signal and the frequency fsc+f (where rL is the color subcarrier frequency of the low frequency converted carrier color signal) , for example 40
Frequency conversion is performed on the difference between the oscillation signal of fH+ (1/8) fH), but since the frequency components above the frequency fsc+ are substantially suppressed by the bandpass filter 8, the aliasing spectrum that occurs during frequency conversion is In addition, the edge frequency division multiplexed signal on the magnetic tape 12a can be substantially suppressed in existing VTs that do not have the reproduction system of the present invention.
Even when the image is reproduced in R, it is possible to add colors to the reproduced image with a certain degree of practicality.

Next, the reproduction system will be described. During reproduction, the switch circuit 3 is switched and connected so as to selectively output the input signal of the terminal P. Signals are recorded on the magnetic tape 12b in the same manner as the signals recorded on the magnetic tape 12a, and the frequency division multiplexed signal is reproduced by the reproducing rotary head 13. This reproduced frequency division multiplexed signal is sent to the preamplifier 14.
The low-frequency converted carrier color signal is returned to the original band reproduced carrier color signal, and the frequency-variable RAM degree signal is supplied to the reproduction signal processing circuit 15 via The signal is FM demodulated and becomes a reproduced luminance signal. The reproduced carrier color signal is directly supplied to the terminal 16a of the switch circuit 16, and is supplied to the terminal 16b of the switch circuit 16 after passing through the two-day delay circuit 17 and the phase inversion circuit 18 in sequence. Here, the reason why the phase inversion circuit 18 is used is to set such a phase relationship since the phase of the color subcarrier in the carrier color signal of the PAL system is inverted every two lines.

On the other hand, the reproduced brightness signal is transmitted to the switch circuit 3. Synchronous separation circuit 4
After the reproduced horizontal peripheral signal is taken out through the PLL 5, it is supplied to the PLL 5. The output signal of the PLL 5 is frequency-divided by 1/4 by the 1/4 frequency divider 6, so that the period τ+(
=1/f3) into a symmetric square wave. The switching circuit 16 is controlled to switch every half cycle τ+/2 of this square wave. Therefore, a reproduced carrier color signal such as 1 schematically shown in FIG. 2(B), which is -2 on the line two days (two lines) before the current reproduced line, enters the terminal 16tl of the switch circuit 16. In addition, the terminal 16a is shown in the same figure (B).
When a reproduced carrier color signal is input to the line schematically shown in FIG.
As schematically shown in C), the line (k
-2) the sampled carrier color signal and the line sampled carrier color signal are alternately synthesized in time series;
This becomes a time division multiplexed signal on the current line. line (k+1)
The same applies as shown schematically in FIG. 2(C).

The reproduced carrier color signal output from this switch circuit 16 is divided into two lines (k-
2) Since the sampling information in 2) and 2) are close to each other, they are substantially equivalent to the sampled carrier color signal obtained by sampling the carrier color signal at a sampling frequency of 2 fs. Therefore, in this case, the Nyquist frequency [N is fS
/2<=392.578 kHz), but fsc
Even through the transmission system in the '+'rN culmability band, fSC±
A band close to 2fN can be substantially obtained, making it possible to widen the band of the reproduced carrier color signal.

The reproduced carrier color signal output from the switch circuit 16 is filtered by a bandpass filter 19 to remove the switching noise in the switch circuit 16 (attenuated to such an extent that this noise does not become a problem at a frequency of fsc±2fN), and then sent to the mixer circuit 20. After being supplied and mixed with the reproduced luminance signal here,
The signal is outputted to the output terminal 21 as a reproduced color video signal.

Note that even if the sampling frequency rs is not selected to be an odd multiple of b+/4, the sampling points are 1/4 of each other every 1H.
It is possible to shift by fs. For example, if the sampling frequency [S is an integral multiple of fH, the phase of the sampling pulse may be shifted by 90' every 111 times.

By the way, in a so-called azimuth recording/playback system VTR in which two heads for recording and playing back adjacent video tracks are set at different azimuth angles to record and form video tracks without guard bands, the azimuth loss effect occurs at low frequencies. Since this is not sufficient, the low frequency converted carrier color signal of the adjacent track is mixed into the playback signal as a crosstalk component, so crosstalk countermeasure processing is applied to the PAL carrier color signal during recording and playback. It is well known that this is necessary. As this crosstalk countermeasure processing, for example, the present applicant has previously proposed
As disclosed in Publication No. 3, only the low frequency conversion carrier color signal of one of two adjacent video tracks is recorded by shifting the phase of the color static 1 carrier wave in a fixed direction by 90' every 1H, During reproduction, the phase of the color subcarrier is substantially shifted in the opposite direction by 90° every 1H only during the reproduction period of the recorded low-pass converted carrier color signal with a phase shift, and the phase is returned to the original state.
Furthermore, by obtaining a reproduced carrier color signal with no phase shift and in the original band, and passing this reproduced carrier color signal through a comb-shaped filter using a 2-day delay circuit, a reproduced carrier from which R0 stoke has been removed is obtained. Recording and reproducing methods for obtaining color signals are known. That is, according to the recording and reproducing method proposed by the present applicant, when reproducing a track of a low-frequency converted carrier color signal recorded with a phase shift, the adjacent The low frequency conversion carrier color signal recorded without phase shift processing of the track is reproduced as a crosstalk whose phase is reversed every two days by this phase shift processing during playback, while the low frequency conversion carrier color signal recorded without phase shift processing is When the carrier color signal is reproduced, the phase shift processing described above is not performed, so the low frequency converted carrier color signal of the adjacent track is reproduced as crosstalk in the signal form with the phase shift, so the phase of the crosstalk is changed every 2H. is reversed. Therefore, by passing the signal through the above-mentioned comb filter, crosstalk is canceled out and a PAL reproduced carrier color signal having line correlation is extracted every 2H.

Therefore, in the present invention, when the PAL carrier color signal is recorded and reproduced by performing the phase shift processing described above every other track (every other field), the output reproduced carrier color at line k of the switch circuit 16 is Crosstalk in the signal is caused by switching between the two lines previous and current carrier color signals every period τ1/2 in such a way that the phase of the color subcarrier continues in a uniform color pattern. As shown by the arrows in FIG. 2(C), the phase should be inverted every +/2, and the frequency is fS. Therefore, the frequency characteristics of the bandpass filter 19 are as shown in FIG.
Crosstalk can be suppressed by selecting a characteristic that sufficiently attenuates the frequency component of fSC±[S. One bandpass filter having such frequency characteristics can also serve to suppress switching noise caused by the switch circuit 16.

Effects of the Invention As described above, according to the present invention, the band hi! fsc± [Sampling the PAL carrier color signal of C, and selecting the sampling period τ1 to be a value larger than 1/(2・fc) and smaller than 1/fc, and 1/fsc≦ Since the gate output is made to transmit the sampled carrier color signal only during the period τ2 that satisfies the inequality τ2 × τ1, fsc
It is possible to pass through a narrowband transmission system that allows signals in a band of ±(rs/2) to pass through, and the sampled carrier color signals of the two previous lines and the current line are alternately switched and output every τ1/2. Therefore, the sampling frequency [S of 2
A carrier color signal equivalent to the carrier color signal sampled at twice the frequency can be obtained, and thus fsc±(fs/2>
Even if a narrowband transmission system with a band of It has a number of features, such as being able to suppress crosstalk from adjacent tracks whose phases differ by 180° by selecting the frequency characteristics of the filter circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the method of the present invention;
FIG. 2 is a diagram showing signal waveforms etc. for explaining the operation of the block system shown in FIG. 1, and FIGS. 3 and 4 are diagrams showing examples of frequency characteristics of each main part in the block system shown in FIG. 1, respectively. , FIG. 5 is a diagram showing an example of the frequency spectrum of a recording signal of a current home VTR. 1...PAL color video signal human power switch terminal...
Y/C separation circuit, 3, 7.16... switch circuit, 4
... Synchronous separation circuit, 5... Phase locked loop (PLL), 6... 1/4 frequency divider, 8... Bandpass filter, 12a, 12b... Magnetic tape, 17...
・2H delay circuit, 18...phase inversion circuit. Figure 2

Claims (1)

[Claims] A PAL carrier color signal having a band of fsc±fc (where fsc is a color subcarrier frequency) is supplied, and {1/(2fc)<τ_1<1/fc, 1/fsc≦ Sampling is performed by gate-outputting the carrier color signal only during the period τ_2 of each period τ_1 that satisfies the inequality τ_2<τ_1}, and the sampling points on two adjacent lines are horizontally scanned by each other. Sampling is performed so that the sampled carrier color signal is shifted by τ_1/4 in the direction, and the sampled carrier color signal obtained thereby is transmitted, and the sampled carrier color signal of the current line and the sampled carrier color signal of the current line are The sampled conveyed color signal of the line two horizontal scanning periods before the line is transferred for a period τ_
A PAL carrier color signal transmission system characterized in that the time division multiplexed signal obtained by this is outputted by switching alternately every 1/2 and outputting as the carrier color signal of the current line.