JPH0632471B2 - Sampling clock phase control system - Google Patents

Description

The present invention relates to the reproduction of a sampling clock of a device for sampling and encoding and transmitting a color television signal, and more particularly to reproduction of a color burst of a transmitter and a receiver. The present invention relates to a sampling clock phase control system for keeping a relative phase of a color television signal with a color burst constant.

[Conventional technology]

When encoding and transmitting a color television signal, if sampling is performed with a sampling clock that is synchronized with the input television signal without being synchronized with the transmission path clock, a method for regenerating the sampling clock at the receiving unit is at a fixed cycle. There is a method in which the frequencies are synchronized so that the number of sampling clocks in the same in the transmitter and the receiver. This is, for example,
No. 2-117613, Sampling Frequency Synchronizer.

[Problems to be solved by the invention]

However, in the above-described conventional system, the sampling clock of the transmission unit and the sampling clock of the reception unit are synchronized only in frequency, and the phase relationship cannot be synchronized. For this reason, when a color television signal is coded and transmitted, the phase of the color burst of the television signal reproduced by the receiver is out of phase with the sampling clock with respect to the phase of the color burst of the input color television signal of the transmitter. Therefore, there is a drawback that the relative phase fluctuates with time. Therefore, when a color television signal is edited using the encoded and transmitted signal, it is necessary to perform phase synchronization of the color burst, and a separate device for phase synchronization such as a frame synchronizer is required. .

[Means for solving problems]

In order to solve such a problem, the sampling clock phase control system according to the present invention comprises a transmitter and a receiver, and the transmitter has a first phase reference phase-synchronized with a color burst of an input color television signal. Means for generating a signal, means for sampling the first phase reference signal at fixed intervals obtained by dividing the transmission path clock, and sampling with the sampled first phase reference signal and sampling clock And a means for multiplexing and transmitting the encoded information of the input color television signal, and the receiving portion decodes the encoded information of the color television signal by using the reproduced sampling clock and outputs the color television. A means for obtaining a signal, a means for generating a second phase reference signal phase-synchronized with the color burst of the decoded color television signal, and a second phase reference signal for each cycle in which the first phase reference signal is transmitted. Means for sampling the phase reference signal, and means for performing phase comparison between the sampled second phase reference signal and the first phase reference signal to obtain a phase difference signal and then smoothing and outputting the phase difference signal. , The sampling frequency is changed while changing the oscillation frequency according to the smoothed phase difference signal and performing feedback control so that the first phase reference signal and the second phase reference signal are maintained in a constant phase relationship. And means for generating it.

[Operation] In the sampling clock phase control system according to the present invention, the color television signal synchronized with the color burst phase of the color television signal of the transmitting portion can be decoded by the receiving portion.

〔Example〕

1 is a block system diagram showing an embodiment of a sampling clock phase control system according to the present invention.
(a) is a transmitter, and FIG. 1 (b) is a receiver. In the block system of FIG. 1, an NTSC color television signal is A / D converted at a frequency three times the subcarrier frequency _sc , band-compressed and coded, and 45 Mb together with color burst phase information.
/ S bit rate is transmitted, and the phase difference between the phase of the color burst of the decoded color television signal and the phase of the color burst of the transmitted transmitter is fixed at the receiver. The case where the sampling clock is generated by feedback is shown.

In FIG. 1, 1 and 11 are input terminals, 2 is an A / D converter, 3 and 9 are clock generation circuits, 3a and 21 are color subcarrier generation circuits, 4 is an encoder, and 5, 7 and 18 are divisions. Circuit, 6, 15 is a sampling circuit, 8 is a multiplexing circuit, 10,
22 is an output terminal, 12 is a separation circuit, 13 and 20 are clock recovery circuits, 14 is a phase comparison circuit, 16 is a decoding circuit, 1
Reference numeral 7 is a smoothing circuit, and 19 is a D / A converter.

The NTSC color TV signal input to the input terminal 1 is A
It is supplied to the / D converter 2, the clock generation circuit 3, and the color subcarrier generation circuit 3a. The clock generation circuit 3 generates a sampling clock synchronized with the frequency of 3 _sc .
This sampling clock is supplied to the A / D converter 2, the encoder 4 and other necessary places. Color TV signal is A /
It is digitized by the D converter 2, band-compressed by the encoder 4, and supplied from the encoder 4 to the multiplexing circuit 8 as encoded information. The color subcarrier generation circuit 3a generates a color subcarrier signal that is phase-synchronized with the color burst of the input color television signal. The frequency dividing circuit 5 quantizes the color subcarrier signal into a binary value and then divides it in half to supply it to the sampling circuit 6 as a first phase reference signal.

The clock generation circuit 9 generates a transmission line clock of 44.736 MHz, the frequency division circuit 7 divides the frequency by 1/4760 corresponding to the cycle of the DS3 multiframe, and outputs the first phase reference signal for each head of the multiframe. Sampling and the sample value is DS
Multiplexing into predetermined time slots of 3 multiframes. In other time slots, band compression coded coded information, control signals, etc. are multiplexed. The multiplexing circuit 8 multiplexes the DS3 frame and U / B-converts the multiplexed signal, and outputs it to the output terminal 10 as a 44.736 MHz bipolar signal.

The bipolar signal input to the input terminal 11 of the receiver is
The clock recovery circuit 13 recovers the 44.736 MHz transmission line clock and supplies it to the separation circuit 12. After the B / U conversion of the bipolar input signal, the separation circuit 12 performs DMPX from the DS3 frame to separate the encoded information / control signal, the first phase reference signal and the pulse signal indicating the beginning of the DS3 frame. Supply to each part.

The clock reproduction circuit 20 generates a sampling clock having an oscillation frequency according to the control signal from the smoothing circuit 17, and the sampling clock is supplied to the decoder 16 and the D / A converter 19. The coded information is decoded by the decoder 16 into a digital color television signal, converted into an analog signal by the D / A converter 19 and supplied to the output terminal 22 and the color subcarrier generation circuit 21. The color subcarrier generation circuit 21 generates a color subcarrier signal phase-synchronized with the color burst of the decoded color television signal and supplies it to the frequency dividing circuit 18. The frequency dividing circuit 18 quantizes the color subcarrier signal into a binary value and then divides it in half to supply it to the sampling circuit 15 as a second phase reference signal. The sampling circuit 15 uses the D obtained by the separation circuit 12.
The second phase reference signal is sampled for each head of the frame of S3 and then supplied to the phase comparison circuit 14.

The phase comparison circuit 14 is the first circuit supplied from the separation circuit 12.
Phase comparison between the second phase reference signal and the phase reference signal of D
It is performed every frame period of S3. The phase comparison is performed by an exclusive OR of the two phase reference signals that have been binarized, and the phase comparison circuit 14 outputs a phase comparison signal represented by a binary value of 0 or 1 and supplies it to the smoothing circuit 17. Smoothing circuit 17
Is digitally integrated with a value of +1 when the phase comparison signal is 1 and with a value of -1 when the phase comparison signal is 0, and after performing sufficient smoothing by the integration, the integrated value is D An analog phase comparison signal that has been A / A converted and smoothed is supplied to the clock recovery circuit 20. The clock recovery circuit supplies the smoothed phase comparison signal to the voltage controlled oscillator to generate a sampling clock having a frequency corresponding to the control voltage. That is, the signal of the color burst phase of the decoded color television signal is accompanied by the fluctuation of the phase of the sampling clock, the D / A converter 19, the color subcarrier generating circuit 21, the frequency dividing circuit 18, the sampling circuit. It is fed back to the phase comparison circuit 14 via 15. Then, the fed-back second phase reference signal and the first phase reference signal are compared in phase, and the phase comparison signal is sent to the clock recovery circuit 20 through the smoothing circuit 17.

Feedback control is performed in this manner, and finally, when the first phase reference signal and the second phase reference signal are in the "H" level or "L" level section, the average is about 50%. Where there is a phase difference, the feedback loop becomes balanced. That is, by performing feedback control so that the relative phase between the first phase reference signal and the second phase reference signal is constant and reproducing the sampling clock, the color burst of the reproduced color television signal is reproduced. The phase can be synchronized with the phase of the color burst of the input color television signal of the transmitter.

FIG. 2 shows a block system for explaining another embodiment of the clock generation circuit 3 and the method of generating the phase reference signal. FIG. 2 (a) shows a transmitting section, and FIG. 2 (b) shows a receiving section. In the figure, the same or corresponding parts as those in FIG. 1 are designated by the same reference numerals.

In FIG. 2, the phase of the sampling point of the color burst of the color television signal digitized by the A / D converter 2 is digitally detected, and the phase difference is fed back to the voltage controlled oscillator to keep a constant value. The clock generation circuit 20 is configured to generate a sampling clock that is phase-synchronized with the color burst of the input television signal by performing the sampling in phase. In this case, even if the color subcarrier generating circuit 3a shown in FIG. 1 is not used, the frequency dividing circuit 5 divides the sampling clock in synchronization with the color burst to generate the first phase reference signal. be able to. In the receiving unit, the sampling clock reproduced in synchronization with the phase of the color burst of the digital color television signal decoded by the decoder is frequency-divided by the frequency dividing circuit 18 to generate the second phase reference signal. Can occur.

〔The invention's effect〕

As described above, according to the present invention, in the transmitting unit, the phase reference signal synchronized with the color burst of the input color television signal is sampled and transmitted for each constant sample of the transmission path clock, and in the receiving unit, the decoded color signal is sampled. Phase synchronization of the color burst can be performed by reproducing the sampling clock while performing feedback control so that the phase of the color burst of the television signal and the phase reference signal sent thereto have a constant phase relationship. Therefore, there is an effect that the color television signal synchronized with the color burst phase of the color television signal of the transmitter can be decoded by the receiver.

[Brief description of drawings]

FIG. 1 is a block system diagram showing an embodiment of a sampling clock phase control system according to the present invention, and FIG. 2 is a block system diagram showing another embodiment. 1, 11 ... Input terminal, 2 ... A / D converter, 3, 9 ...
... Clock generation circuit, 3a, 21 ... Color subcarrier generation circuit, 4 ... Encoder, 5, 7, 18 ... Frequency division circuit, 6, 15 ... Sampling circuit, 8 ... Multiplexing circuit, 1
0,22 ... Output terminal, 12 ... Separation circuit, 13, 20
...... Clock regeneration circuit, 14 …… Phase comparison circuit, 16 ・ ・ ・
... Decoding circuit, 17 ... Smoothing circuit, 19 ... D / A converter.

Claims (1)

[Claims] 1. A sampling clock phase control system which synchronizes sampling clocks on a transmitting side and a receiving side in the case of encoding and transmitting a digital signal obtained by sampling a color television signal, comprising a transmitter and a receiver, The transmitter includes means for generating a first phase reference signal phase-synchronized with the color burst of the input color television signal;
Means for sampling the first phase reference signal at fixed intervals obtained by dividing the transmission path clock, and an input color television sampled by the sampled first phase reference signal and sampling clock. And a means for multiplexing and transmitting the coded information of the signal, wherein the receiving section obtains a color television signal by decoding the coded information of the color television signal using the reproduced sampling clock. Means for generating a second phase reference signal that is phase-synchronized with the color burst of the decoded color television signal, and means for sampling the second phase reference signal in each cycle in which the first phase reference signal is transmitted. And means for performing phase comparison between the sampled second phase reference signal and the first phase reference signal to obtain a phase difference signal and then smoothing and outputting the phase difference signal, and the smoothed phase difference signal According to the transmission frequency And a means for generating a sampling clock while performing feedback control so that the first phase reference signal and the second phase reference signal are kept in a constant phase relationship by changing Clock phase control system.