JP2676805B2 - Sampling clock phase control system - Google Patents

Description

The present invention relates to an apparatus for sampling and encoding and transmitting a color television signal, and more particularly to a color burst of a transmitting section and a color burst of a color television signal reproduced by a receiving section. The present invention relates to a sampling clock phase control system that keeps the relative phase of the constant.

[Prior Art] When encoding and transmitting a color television signal, when sampling is performed with a sampling clock that is synchronized with the input television signal without being synchronized with the transmission path clock, as a method of reproducing the sampling clock in the receiving section There is one that synchronizes the frequency so that the number of sampling clocks in a fixed cycle is the same in the transmitter and the receiver (Japanese Patent Application No. 52-117613 "Sampling Frequency Synchronizer").

[Problems to be solved by the invention]

In the conventional system described above, the sampling clock of the transmitter and the sampling clock of the receiver are synchronized only in frequency, and the phase relationship cannot be synchronized. Therefore, the color television signal is coded and transmitted. In this case, it is said that the phase of the color burst of the television signal reproduced by the receiver fluctuates temporally with respect to the phase of the color burst of the input color television signal of the transmitter due to the phase shift of the sampling clock. There are drawbacks. Therefore, when the color television signal is edited using the encoded and transmitted signal, it is necessary to perform the phase synchronization of the color burst.
A separate device for phase synchronization such as a frame synchronizer was needed.

[Means for solving the problem]

The sampling clock phase control system of the present invention comprises a transmitter and a receiver, wherein the transmitter has means for generating a first phase reference signal phase-synchronized with a color burst of an input color television signal, and a transmission line. Means for sampling the first phase reference signal into a PCM signal at fixed intervals obtained by dividing the clock;
Means for sampling the input color television signal with a sampling clock, the sampled first phase reference signal, and the encoded information of the input color television signal sampled with the sampling clock are multiplexed and transmitted. And a means for obtaining the color television signal by decoding the encoded information of the color television signal using the regenerated sampling clock, and the color burst of the decoded color television signal. Means for generating a second phase reference signal that is phase-synchronized with, and means for sampling the second phase reference signal for each period in which the first phase reference signal is transmitted to obtain a PCM signal. Means for obtaining the cross-correlation between the second phase reference signal and the first phase reference signal, and the first phase reference signal and the second phase reference signal for changing the oscillation frequency according to the value of the cross correlation. Constant phase And a means for generating a sampling clock while performing feedback control so as to maintain the relationship.

[Action]

Therefore, the color television signal synchronized with the color burst phase of the color television signal of the transmitter can be decoded by the receiver.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a sampling clock phase control system of the present invention. FIG. 1 (a) is a block diagram of a transmitter and FIG. 1 (b) is a block diagram of a receiver. .

In the present embodiment, the NTSC color television signal is A / D converted at a frequency of m / n times the horizontal synchronizing frequency _H , for example, a frequency of m / n = 682.5, band-compressed and encoded, and 45 Mb / s together with phase information of the color burst. At the bit rate of, and the receiver feeds back the phase difference so that the phase of the color burst of the decoded color television signal and the phase of the color burst of the transmitted transmitter have a constant phase relationship. To generate a sampling clock.

As shown in FIG. 1 (a), the transmitter has an input terminal 1
, A / D converter 2, clock generation circuits 3 and 9, and encoder 4
, Color subcarrier generation circuit 5, and sampling circuit 6
, A frequency dividing circuit 7, a multiplexing circuit 8 and an output terminal 10. The receiving unit, as shown in FIG.
Input terminal 11, separation circuit 12, clock recovery circuit 13, 18
, A cross-correlation calculation circuit 14, a sampling circuit 15, and a decoder 16
And a D / A converter 17 and a color subcarrier generation circuit 19.

NTSC color TV signal input to input terminal 1 is A / D
It is supplied to the converter 2, the clock generation circuit 3, and the color subcarrier generation circuit 5. The clock generation circuit 3 generates a sampling clock of m / n times the horizontal synchronizing frequency _H. This sampling clock is supplied to the A / D converter 2, the encoder 4 and other necessary places. The color television signal is digitized by the A / 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 5 generates a color subcarrier signal which is phase-synchronized with the color burst of the input color television signal and supplies it to the sampling circuit 6 as a first phase reference signal. Clock generation circuit 9 is 44.736MHz
, And the frequency dividing circuit 7 divides the frequency by 1/4760, which corresponds to the cycle of the multiframe of the third group DS3 of the multiplexed hierarchies in North America. The sampling circuit 6 multi-values the first phase reference signal for each head of the multi-frame, for example, 6
Bit, sample. The multiplexing circuit 8 multiplexes the sampled PCM signal into a predetermined time slot of a DS3 multiframe, and multiplexes band compression coded coded information control signals and the like into the other time slots. The multiplexed signal is U / B converted and output to the output terminal 10 as a 44.736 Mb / s bipolar signal.

The clock regenerating circuit 13 of the receiving unit regenerates the 44.736 MHz transmission line clock from the bipolar signal input to the input terminal 11 and supplies it to the separating circuit 12. The separation circuit 12 B / U-converts the bipolar input signal, demultiplexes it from the DS3 frame, encodes information / control signals, etc., and outputs a pulse indicating the first phase reference signal X _i and the beginning of the DS3 frame. The signal is separated and supplied to each part. The clock recovery circuit 18 generates a sampling clock having an oscillation frequency according to the control signal from the cross-correlation calculating circuit 14, and the sampling clock is decoded by the decoder.
16 and D / A converter 17. The decoder 16 decodes the coded information to obtain a digital color television signal.
This digital color television signal is converted into an analog signal by the D / A converter 17 and supplied to the output terminal 20 and the color subcarrier generation circuit 19. The color subcarrier generation circuit 19 generates a color subcarrier signal that is phase-synchronized with the color burst of the decoded color television signal,
The second phase reference signal Y _i is supplied to the sampling circuit 15.
The sampling circuit 15 samples the second phase reference signal Y _i for each head of the DS3 frame obtained by the separation circuit 12 and supplies the PCM signal to the cross-correlation calculation circuit 14. Cross-correlation calculation circuit
Reference numeral 14 detects a phase shift by obtaining the cross-correlation between the first phase reference signal and the second phase shift reference signal for each DS3 frame period. The cross-correlation coefficient of X _i and Y _i is obtained for the previous K samples, for example, 64 samples. The obtained cross-correlation coefficient is digitally integrated for each frame period of DS3, sufficiently smoothed by integration, and then the integrated value is D / A converted and supplied to the clock recovery circuit 18.
The calculation of the cross-correlation coefficient may be simplified and a value obtained by appropriately normalizing the variance of X _i and Y _i may be used instead. Clock recovery circuit
18 supplies the integrated cross-correlation coefficient signal to a 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 subjected to cross-correlation calculation via the D / A converter 17, the color subcarrier generation circuit 19, and the sampling circuit 15 with the phase fluctuation of the sampling clock. It is fed back to the circuit 14. Then, the cross-correlation between the fed-back second phase reference signal and the first phase reference signal is calculated, and the integrated cross-correlation coefficient signal is sent to the clock recovery circuit 18.

In this way, feedback control is performed, and finally the phase difference between the two becomes 90 ° and the cross-correlation coefficient becomes zero.
The feedback becomes balanced where 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 phase of the color burst of the reproduced color television signal can be synchronized with the phase of the color burst of the input color television signal of the transmitter.

If the transmission path has a frame structure, the present invention can be applied to not only DS frames but also optical transmission paths.

〔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 the drawings]

1 (a) and 1 (b) are block diagrams showing an embodiment of the sampling clock phase control system of the present invention. 1,11 …… Input terminal, 2 …… A / D converter, 3,9 …… Clock generator, 5,19 …… Color subcarrier generator, 4 …… Encoder, 6,15 …… Sampling Circuit, 7 ... Divider circuit, 8 ... Multiplexer circuit, 10,20 ... Output terminal, 12 ... Separation circuit, 13,18 ... Clock recovery circuit, 14 ... Cross-correlation calculation circuit, 16 ... Decoder, 17 ... D / A converter.

Claims (1)

(57) [Claims] 1. A transmission unit and a reception unit, wherein the transmission unit generates a first phase reference signal phase-synchronized with a color burst of an input color television signal,
Means for sampling the first phase reference signal into a PCM signal at fixed intervals obtained by dividing the transmission line clock, means for sampling the input color television signal with a sampling clock, and And a means for multiplexing and transmitting the first phase reference signal and the coded information of the input color television signal sampled by the sampling clock, wherein the receiving unit receives the reproduced sampling clock. Means for decoding the coded information of the color television signal to obtain a color television signal, means for generating a second phase reference signal phase-synchronized with the color burst of the decoded color television signal; Means for sampling the second phase reference signal into a PCM signal for each cycle in which the phase reference signal is transmitted, and a cross-correlation between the sampled second phase reference signal and the first phase reference signal Means to ask, Means for generating a sampling clock while performing feedback control so that the oscillation frequency is changed according to the value of the cross-correlation so that the first phase reference signal and the second phase reference signal are maintained in a constant phase relationship; Sampling clock phase control system with.