JPS592230B2 - Color TV signal converter - Google Patents

Description

[Detailed description of the invention] The present invention relates to a color television signal conversion device.

NTSC, PAL known as broadcast television signals
, SECAM, etc. are all signals in which a subcarrier fsc is modulated by a color signal and frequency multiplexed with a luminance signal. The transmission lines and transmission equipment for transmitting such frequency-multiplexed color television signals (hereinafter abbreviated as FDM signals) are controlled so that the amplitude and phase characteristics are flat over a wide frequency band. This requires transmission paths and equipment with stricter standards than in the case of black-and-white television. On the other hand, in a time-division multiplexed color television signal (hereinafter abbreviated as TDM signal) in which the color signal is time-compressed and time-division multiplexed with the luminance signal, both the color signal and the luminance signal are baseband signals. , its properties are essentially the same as those of black-and-white television signals, and it has the advantage that the standards of the transmission path and transmission equipment may be the same as those for black-and-white television signals. Therefore, when transmitting a color television signal through a transmission line whose quality is for black and white television, it is effective to convert the FDM signal into a TDM signal and transmit the signal. However, in conventional TDM signals, only the color signal is time-compressed and time-division multiplexed with the luminance signal, so the frequency bandwidth of the color signal is extremely narrow, resulting in the disadvantage that the color signal cannot be reproduced sufficiently. It was hot. The present invention provides a TDM without the above-mentioned drawbacks.
A signal conversion device for obtaining a signal is provided.
That is, in the present invention, the FDM signal is demodulated to obtain a baseband luminance signal and a chrominance signal, time compression is performed on both the luminance signal and chrominance signal, and these are time-division multiplexed together with a synchronization signal to produce a baseband luminance signal and a chrominance signal. In this embodiment, a TDM color television signal having a reproduction frequency bandwidth equivalent to that of an FDM signal can be obtained even for color signals. Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 compares and shows signal waveforms of an NTSC signal, a conventional TDM signal, and a TDM signal of the present invention during one horizontal scanning period. In the NTSC signal (waveform A in the figure), one horizontal scanning period TH is the synchronization period Ts) burst period TB
, , FDM signal period TY. The conventional TDM signal (waveform B in the figure) consists of a narrow synchronization period Ts', a color signal period Tc, and a luminance signal period TY, where Tc is TY
During this period, time-compressed color signals are inserted line-sequentially. The TDM signal of the present invention (waveform C in the figure) is composed of a synchronization period Ts', a color signal period Tc', and a luminance signal period TY', and Tc'>TOTY'
<TY. Now, Ts'=T85=ATs'Td=B
If Tc, TV=CTY.

It is.

When TY//Tc-8, b-1.8 at C-0.9
, C=0.8 and b=2.6. In other words, if the luminance signal is time-compressed to 90% to 80%, it is possible to provide a color signal band that is 1.8 to 2.6 times that of the conventional TDM signal.
I) The bandwidth is equivalent to the color signal of the M signal. The time compression rate of the color signal is ``Tc7TY=BTc/TY, so T
When Y/Tc-8, b/8, that is, C-0.9 is 0
．． 225, C-0.8 becomes 0.325. in this case,
The reproduction bandwidth of the luminance signal is 90 to 80% of that of black-and-white television, or the frequency bandwidth of the reproduction luminance signal of the FDM signal is substantially narrower than that of black-and-white television due to the insertion of a subcarrier removal filter. The quality of the luminance signal is not compromised. Figure 2 shows Tsl when C-0.9.
, Td, TY'' and the transmission line bandwidth to 4M.
This shows the reproduced signal band in Hz. In this numerical example, the time compression rate of the color signal is Td/TY-(
Td/TV) Because it is XC (10.6/4.72)×
It is 0.9÷0.20. The time width of the synchronization signal is the same as the conventional T.
In the case of DM system, T8'=TH-TY-TC, so when TY/Tc-8, Ts'=TH-1,125T
Y=63.5-1.125×47.2/0.9÷4.5
The time was 1 μ seconds, but in this numerical example, it has been increased to 5.7 μ seconds. Correspondingly, the time compression rate of the color signal is set to be slightly larger than the above-mentioned time compression rate of 0.225 at C-0.9. Note that a specific method for reducing the color time compression rate to 1/5 will be described later. That is, the reproduction bandwidth of the color signal is 0.81 MHz, and even if losses in the time compression process are taken into account, the color signal band of 0.6 MHz of the NTSC signal can be sufficiently reproduced. On the other hand, in the conventional TDM signal, the reproduction bandwidth of the color signal is 0.5 MHz, and the effective bandwidth is at most 0.5 MHz, considering the loss in the time compression process.
Since the frequency is 4 MHz, the reproduced color signal bandwidth is expanded by 50% according to the present invention. FIG. 3 is a block diagram of a color television signal converter according to the present invention.

The FDM signal 1 is demodulated by a demodulation circuit 2 into a luminance signal Y and line sequential color signals C1/C2. Luminance signal Y, color signal C
The frequency bands and amplitudes of C1 and C2 are adjusted to specified values within the demodulation circuit 2. The luminance signal and the color signal are time-compressed by time compressors 3 and 4, respectively, and then enter a multiplexer 7 where they are time-division multiplexed. On the other hand, the synchronization signal of the FDM signal is extracted by the synchronization separation circuit 5, and the horizontal synchronization signal 9 is used as a control signal for the time compression devices 3 and 4. A color discrimination code is added to the composite synchronization signal 10 by a color discrimination code adding circuit 6, and the signal is input to a multiplexer 7 together with a luminance signal and a color signal, and a TDM signal 8 is synthesized therein.
The color discrimination code is used to identify a TDM color television signal and to determine the order of line-sequential color signals, and is inserted, for example, in a part of the vertical blanking period. Next, the time compression device which plays a central role in the present invention will be explained in detail.

FIG. 4 is a block diagram showing an example of a luminance signal time compression device. The luminance signal 11 is sampled by the sampling circuit 12 by firing the frequency f1 by the oscillator 171. 1
5 and 15' are analog or digital storage circuits, and a shift register or addressable memory is used.

If the storage circuit is of a digital type, the signal sample values are converted into a combination of binary codes by the encoding circuit 13 before entering the storage circuit, and the storage circuit output is converted into an analog signal by the decoding circuit 16. If the memory circuit is analog type (
For example, capacitor memory and charge-coupled devices are used)
Encoding and decoding circuits are not required. The signal is sampled by a switch circuit 14 for each scanning line by storage circuits 15 and 15.
' is written with a pulse of frequency f1. F
An oscillator 172 with a frequency of 2>f1 is used to read the contents of the memory circuit. That is, the clock pulses of the memory circuits are controlled for each scanning line by the changeover switch 18 so that the memory circuit that is not in the write state is brought into the read state by the pulse of frequency F2. The switching switch 14' on the output side is for alternately switching the memory circuit in the read state, and the output 19 has (
It can be seen that a luminance signal whose time is compressed by f1/F2) times is obtained. In FIG. 4, by synchronizing the phase of the sampling pulse of frequency f1 obtained by the oscillator 171 with the horizontal synchronization signal, it is possible to prevent image quality deterioration due to deviation of the sampling position between scanning lines. A simple method for this purpose is to use, in place of the oscillator 171, a circuit that multiplies the subcarrier F8O produced by the demodulation circuit by (m/n) times (M and n are integers). For example, if the FDM signal is NT
For SO signal, the subcarrier frequency F8C is about 3.58M
Hz, and if this is doubled and 7.16 MHz is used as the sampling frequency f1, a luminance signal in the approximately 3.5 MHz band can be reproduced.Moreover, the phase of the sampling pulse is synchronized with the horizontal synchronizing signal. Therefore, good image quality can be obtained without shifting the sampling position between scanning lines. By synchronizing the phase with the horizontal synchronization signal even when using a readout clock pulse of frequency F2, a high-quality TD with no phase jitter can be achieved.
M signal can be obtained. When f1=7.16MHz, F2 is required to time-compress the luminance signal to 90%.
is approximately 8 MHz. For example, as shown in FIG. 8, a method of obtaining a pulse of frequency F2 that is phase-synchronized with the horizontal synchronizing signal is to divide the output of the frequency oscillator 177, which is N times F2, into a counter 200 by a factor of N, There is a method of reducing the phase error of F2 to 1/N by resetting it for each scan using the horizontal synchronizing signal 9. Alternatively, as shown in FIG. 9, the output of the voltage controlled oscillator 51 is divided by a frequency divider 200', the phase is compared with the horizontal synchronizing signal by a phase comparator 50, and the output is There is a method of obtaining a pulse of frequency F2 that is phase-locked to the horizontal synchronizing signal by feeding it back to the voltage controlled oscillator. FIG. 5 is a block diagram showing another embodiment of the time compression device for luminance signals. Oscillator 172 generates clock pulses with a frequency of 1/T and 2
, gate circuits 201 and 202 respectively exchange the pulses φ1 and φ2 with pulses φ1 and φ2 as shown in FIG. 6 with the same number of pulses and different pulse intervals. That is, φ1
is a pulse that samples the signal and writes it into the memory circuit, and the interval is 2T near both ends of the luminance signal period TY, and is T near the center. φ2 is a clock pulse for reading out the contents of the memory circuit, and the interval is T over the entire period TY'. In the case of 90% time compression, φ1 is set as a pulse with an interval of 2T within a range of 10% at each end (TYO).

That is, this device compresses the time of the luminance signal non-uniformly, so that the time is compressed to 1/2 at the periphery of the screen, and no time is compressed near the center. like this. When time compression is performed, the phase relationship between φ1 and φ2 is constant, so
There is an advantage that time compression can be achieved using one addressable memory 15. 11, 12, 1 in Figure 5
3, 15, 16, 19 have the same functions as in Figure 4, and memory 1
At address No. 5, the outputs of the write address generation circuit 213 and the read address generation circuit 214 are switched and applied by the switch circuit 215, and time compression is performed by one memory. In this case, as in the above case, by synchronizing the phases of the clock pulses φ1 and φ2 with the horizontal synchronizing signal, deterioration in quality due to jitter can be prevented. FIG. 7 is a block diagram showing a color signal time compression device.

The configuration is almost the same as that in FIG. 4, and parts with the same functions are designated with the same numbers. In the case of Tc'〈(TH-TY), the writing and reading times of the memory circuit can be distributed within the same horizontal period, so only one memory circuit (shift register or addressable memory) is required as shown in the figure. It can be composed of The pulse of frequency FA generated by the oscillator 271 is used as a clock pulse for sampling the signal and writing to the memory circuit, and the pulse of frequency F generated by the oscillator 272
The pulse B (FA<FB) is used as a clock pulse for reading the memory circuit. Further, in the figure, numeral 21 is a color signal, and 25 is a delay circuit for obtaining a time-compressed color signal 29 having a predetermined time relationship with the synchronization pulse. Instead of the oscillators 271 and 272 in the chrominance signal time compression device as described in the luminance signal time compression device,
The subcarrier frequency Fsc already created by the demodulation circuit is (m/
n) The device can be simplified by using a circuit that multiplies by a factor of two.
It becomes 2 singles.

For example, if a multiplier circuit with FA=100 Fsc and fB=2 fsc is used, pulses of frequencies FA and fB are both phase synchronized with the horizontal synchronizing signal, and no jitter occurs in the color signal. In this case, the color signal is time-compressed to 1/5, and Fsc=3
．． In the case of 58 MHz, color signals in the approximately 0.71 VF-1z band can be reproduced. Incidentally, FA and fB can also be generated from the readout clock pulse in a luminance signal time compression device. Also, FA=Fsc/2, fB=2fs
Combinations such as c can be used.

[Brief explanation of the drawing]

FIG. 1 shows a comparison of waveforms of an NTSC signal, a conventional TDM signal, and a TDM signal of the present invention.

Claims (1)

[Claims] 1. A means for demodulating a color television signal obtained by frequency multiplexing a luminance signal and a chrominance signal modulated with a subcarrier into a baseband luminance signal and a chrominance signal, and a means for demodulating the demodulated luminance signal into a baseband luminance signal and a color signal, and
Means for time-compressing 0 to 90% and color signal to 20 to 33% in units of one horizontal scanning period, time-division multiplexing of the time-compressed luminance signal and color signal, and adding a synchronization signal and color discrimination code. and means for obtaining a time-division multiplexed color television signal.