JPH0431236B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a PAL color carrier color signal transmission system, and is particularly useful in a carrier color signal transmission system with a limited band such as a VTR.
This invention relates to a transmission method for transmitting a PAL carrier color signal.

Conventional technology and problems Video signal recording and reproducing devices, especially home VTRs, are not used for broadcasting due to demands for lower prices and smaller size.
Compared to a VTR, the mechanical and electrical systems are simpler, so the relative linear velocity between the tape and the head is slower, and the transmission band is sufficient to record and play back the entire color video signal by frequency modulating it. In addition, there are large fluctuations in the time axis. For this reason, current home use
Most VTRs use a standard color video signal that is separated into a luminance signal and a carrier color signal, and the luminance signal is used to frequency modulate (FM) a low frequency carrier wave, resulting in frequency modulation of the frequency spectrum as shown in Figure 5. The carrier chrominance signal is frequency-converted to a lower frequency range to make it less susceptible to the influence of reproduction time axis fluctuations, and these two signals are frequency-divided as a carrier chrominance signal with a frequency spectrum as shown in Fig. 5. As is well known, it uses a low-frequency conversion recording and playback method in which multiplexed signals are recorded on magnetic tape, and during playback, signal processing operations are performed in the opposite direction to those during recording to obtain reproduced color video signals. .

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

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

Means for Solving the Problems The present invention provides a PAL carrier color signal with a band of sc±c (where sc is the color subcarrier frequency).
The gate outputs only for a certain period τ ₂ every period τ ₁ ,
A sampled carrier color signal is transmitted in which sampling points on two adjacent lines are sampled such that they are shifted from each other by τ ₁ /4 in the horizontal scanning direction. Here, the above τ ₁ and τ ₂ are selected to values that satisfy the following inequality.

1/(2c)<τ ₁ <1/c 1/sc≦τ ₂ <τ ₁ The transmitted sampled carrier color signals are two types of sampled carrier color signals: the current line and the line two horizontal scanning periods ago. After that, the signals are alternately switched and output every period τ ₁ /2.

Effect Among the transmitted sampled carrier color signals, if both the sampled carrier color signals of the current line and the line two horizontal scanning periods earlier than the current line are switched and outputted alternately every τ ₁ /2, the obtained result is obtained. The time-division multiplexed signal obtained is a carrier color signal sampled at a sampling frequency substantially twice the sampling frequency s (=1/τ ₁ ) in the transmission system (recording system). Therefore, even if a transmission path can only transmit signals in a band of about sc±(1/2)s, the signal in a band of sc±c, which is wider than the transmission band, can be transmitted.
The PAL carrier color signal 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 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 the synchronization separation circuit 4 passes through the switch circuit 3 connected to the terminal R side. 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 frequency (2n-1) _.H which is an odd multiple of the horizontal scanning frequency _H. (However, n is a natural number, for example, n=101) and generates and outputs a symmetrical square wave. This symmetrical square wave is fed to the 1/4 frequency divider 6, where the 1/4
After being frequency-divided into a symmetrical square wave with a repetition frequency of (2n-1)· _H /4, it is applied to the switch circuit 7 as a switching signal.

Here, if the repetition frequency of the output symmetric square wave of the 1/4 frequency divider 6 is s and the period is τ ₁ (=1/s),
Since the repetition frequency s is an odd multiple of _H /4 as described above, the phase differs by 90°, that is, τ ₁ /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 from each other by τ ₁ /4 in two adjacent lines.

On the other hand, the carrier color signal in the band sc±c is separated from the input PAL color video signal by the Y/C separation circuit 2 (where sc is the color subcarrier frequency).
4.43MHz, and c is a frequency of about 500kHz, for example)
is supplied to the switch circuit 7. switch circuit 7
is turned on during the high level period τ ₂ (here, τ ₂ = τ ₁ /2) of the output symmetrical square wave of the 1/4 frequency divider 6, selects and outputs the input carrier color signal, and outputs the input carrier color signal during the low level period τ ₁ −τ ₂ is turned off to prevent passage of the input carrier color signal. Therefore, the input carrier chrominance signal is gated out to the bandpass filter 8 as a sampled signal (sampled carrier chrominance signal) only during period τ ₂ of every period τ ₁ .

Here, the above period τ ₁ is 1/(2c)<τ ₁ <1/c
The first inequality holds that 1/sc≦τ ₂ <τ ₁ , and the second inequality holds that 1/sc≦τ 2 <τ 1
A value that satisfies both of the inequalities is selected. Therefore, the above period τ ₁ is, for example, 4/20 of the horizontal scanning period.
Selected for 1x period. In this case, the repetition frequency s of the symmetrical square wave applied as a switching signal to the switch circuit 7 is the horizontal scanning frequency.
The frequency is 785.156kHz, which is 201/4 times the frequency of 15.625kHz.

In this way, the sampled carrier signal taken out from the switch circuit 7 can be any of the k-2, k-1, k, and k+1th 4 in one field.
Each of the book lines has a waveform and phase relationship as shown in FIG. 2A. As can be seen from FIG. 2A, the sampled carrier color signal has a sampling frequency s (=1/τ ₁ ) of _H /τ as described above.
Since the sampling point (signal portion of period τ ₂ ) is selected as an odd multiple of 4 (201· _H /4 in the above example), two adjacent lines are separated by τ ₁ /4 from each other in the horizontal scanning direction. The signal is shifted to Further, as shown in FIG. 2A, this sampled carrier color signal is a burst wave with a duration τ ₂ and a period τ ₁ , and is converted into a continuous wave by the bandpass filter 8.

As shown in FIG.
The frequency characteristics are selected to wave frequency components in the sc±s band. This band filter 8
The sampled carrier color signal that has passed through 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. Frequency division multiplexing is performed on the frequency modulated wave signal. 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.
As a result, a video track is formed and recorded on the running magnetic tape 12a.

Here, in the recording signal processing circuit 9, when converting the frequency of the sampled carrier color signal to a lower frequency band, the sampled carrier color signal and the frequency sc+ _L
(However, _L is the color subcarrier frequency of the low-pass conversion carrier color signal, and the difference frequency is converted between it and the oscillation signal of, for example, 40 _H + (1/8) ( _H ). Since frequency components higher than the frequency sc+ _L are substantially suppressed, it is possible to substantially suppress the aliasing spectrum that occurs during frequency conversion. not existing
Even when reproduced on a VTR, it is possible to add colors that have some practicality to the reproduced image.

Next, the reproduction system will be described. During reproduction, the switch circuit 3 is connected 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 supplied to the reproduced signal processing circuit 15 via the preamplifier 14, where the existing
Similar to the reproduction system of a VTR, the low frequency converted carrier color signal is returned to the reproduced carrier color signal of the original band, and the frequency modulated luminance signal is FM demodulated to become the reproduced luminance signal. The reproduced carrier color signal is connected to terminal 1 of the switch circuit 16.
6a directly, while the 2H delay circuit 17
and the switch circuit 1 through the phase inversion circuit 18.
6 is supplied to terminal 16b of No. 6. 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 is inverted every two lines in the carrier color signal of the PAL system.

On the other hand, the reproduced luminance signal passes through the switch circuit 3 and the synchronization separation circuit 4, and after the reproduced horizontal synchronization signal is extracted, it is supplied to the PLL 5. The output signal of PLL5 is 1/4
By dividing the frequency by 1/4 by the frequency divider 6, it is converted into a symmetrical square wave with a period τ ₁ (=1/s) as described above. The switch circuit 16 is controlled to switch every half cycle τ ₁ /2 of this square wave. Therefore, the line k-2 which is 2H (two lines) before the current reproduction line k is connected to the terminal 16b of the switch circuit 16.
When a reproduced carrier color signal as schematically shown in FIG. 2B is received, and a reproduced carrier color signal of line k schematically shown in FIG. 2B is input to the terminal 16a, the switch circuit As schematically shown in FIG. 2C, the output reproduced carrier color signal of No. 16 alternates between the sampled carrier color signal of line (k-2) and the sampled carrier color signal of line k every period τ ₁ /2. The time-division multiplexed signal of the current line k is synthesized in time series. The same applies to line (k+1) as schematically shown in FIG. 2C.

As can be seen from FIG. 2B and C, the output reproduced carrier color signal of this switch circuit 16 is sampled because the sampling information of the two lines (k-2) and k are similar to each other. This is substantially equivalent to the sampled carrier color signal obtained by sampling at a frequency of 2s. Therefore, in this case, the Nyquist frequency _N is s/2 (=392.578kHz)
However, even through a transmission system with a band on the order of sc± _N , a band close to sc± _2N 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 switching noise in the switch circuit 16 (attenuated to such an extent that this noise does not become a problem at a frequency of sc±2 _N ), and then further filtered by a mixing circuit. 20, where it is mixed with a reproduced luminance signal and then outputted to an output terminal 21 as a reproduced color video signal.

Note that even if the sampling frequency s is not selected to be an odd multiple of _H /4, the sampling points can be shifted from each other by 1/4 s every 1H.
For example, if the sampling frequency s is an integral multiple of _H , the phase of the sampling pulse may be shifted by 90 degrees every 1H.

By the way, in a so-called azimuth recording and reproducing type VTR in which two heads that record and reproduce adjacent video tracks are set at different azimuth angles to record and form video tracks without guard bands,
Since the azimuth loss effect is not sufficient for low frequencies, the low-frequency converted carrier color signal of the adjacent track is mixed into the playback signal as a crosstalk component, which causes the PAL carrier color signal to be mixed into the PAL carrier color signal during recording and playback. It is well known that it is necessary to take measures against crosstalk. As this crosstalk countermeasure processing, for example, as previously disclosed by the present applicant in Japanese Patent Publication No. 55-32273, two adjacent
Only one low-pass converted carrier color signal of the book's video track is recorded with the phase of its color subcarrier shifted in a fixed direction by 90 degrees every 1H, and during playback, the low-pass converted carrier color signal is recorded with a phase shift. Only during the reproduction period, the color subcarrier is shifted in phase substantially in the opposite direction by 90° every 1H and the phase is returned to the original state, and then the reproduced carrier color signal with no phase shift and the original band is generated. A recording/reproducing method is known in which a reproduced carrier color signal from which crosstalk has been removed is obtained by passing this reproduced carrier color signal through a comb filter using a 2H delay circuit. In other words, 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 crosstalk whose phase is reversed every 2H 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 its phase shifted, so the phase of the crosstalk is changed every 2H. is reversed. Therefore, by passing through the above 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 recording and reproducing the PAL carrier color signal by performing the above phase shift processing every other track (every other field), the output reproduction carrier at line k of the switch circuit 16 Crosstalk in the color signal is caused by switching between the carrier color signal two lines before and the current carrier color signal every period τ ₁ /2 in such a way that the phase of the color subcarrier continues in a uniform color pattern. Therefore, as shown by the arrow in FIG. 2C, the phase should be inverted every τ ₁ /2, and the frequency is s. Therefore, crosstalk can be suppressed by selecting the frequency characteristics of the band filter 19 to sufficiently attenuate the frequency components of sc±s, as shown in FIG. The band filter 19 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 carrier color signal of the PAL system in the band sc±c is adjusted so that the sampling points on two adjacent lines are shifted from each other by τ ₁ /4 in the horizontal scanning direction. , and the sampling period τ ₁ is larger than 1/(2・c),
Select a value smaller than 1/c, and 1/sc≦τ ₂ <
Since the sampled carrier color signal is transmitted by gate output for the period τ ₂ that satisfies the inequality τ ₁ , it passes through a narrowband transmission system that allows signals in the band of sc±(s/2) to pass. The sampled carrier color signals of the two lines before and the current line can be expressed as τ ₁ /
Since the output is switched alternately every 2, it is possible to obtain a carrier color signal equivalent to a carrier color signal sampled at a frequency that is substantially twice the sampling frequency s, and thus sc±(s/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° from each other by selecting the frequency characteristics of the filter circuit.

[Brief explanation of drawings]

FIG. 1 is a block system diagram showing an embodiment of the system 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.
Each figure shows an example of the frequency characteristics of each main part in the block system shown in Figure 1, and Figure 5 shows an example of the frequency characteristics of the main parts in the block system shown in Figure 1.
FIG. 3 is a diagram showing an example of a frequency spectrum of a recording signal of a VTR. 1...PAL color video signal input terminal, 2...
Y/C separation circuit, 3, 7, 16...switch circuit,
4... Synchronous separation circuit, 5... Phase locked loop (PLL), 6... 1/4 frequency divider, 8... Bandwidth filter, 12a, 12b... Magnetic tape, 17... 2H delay circuit, 18... Phase inversion circuit.

Claims (1)

[Claims] 1. A PAL carrier color signal having a band of sc±c (where sc is the color subcarrier frequency) is supplied, and 1/(2c)<τ ₁ <1/c 1/sc≦ Sampling is performed by gate-outputting the carrier color signal only during a period τ ₂ for each period τ ₁ that satisfies the inequality τ ₂ < τ ₁ , and the sampling points on two adjacent lines are Sampling is performed so as to be shifted from each other by τ ₁ /4 in the horizontal scanning direction, and the sampled carrier color signals obtained thereby are transmitted, and among the transmitted sampled carrier color signals, the sampled carrier color of the current line is signal and the sampled carrier color signal of the line two horizontal scanning periods before the current line for a period τ ₁ /2.
A PAL carrier color signal transmission method, which is characterized in that the time-division multiplexed signal obtained by this is outputted as the carrier color signal of the current line.