JPH0417516B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is transmitted by inserting a burst signal into a regular television signal within a certain interval indicating the horizontal synchronizing signal position and at the beginning of a frame indicating the duplex synchronizing signal. From the composite video signal, in the receiving section,
This invention relates to a clock signal generator that generates continuous clock pulses synchronized with this burst signal.

Conventional configurations and their problems In recent years, with the spread of image transmission services such as ITV, there has been an increasing demand for color images, but the color transmission system (NTSC system) used for broadcasting uses color signals. Since the luminance signal is frequency multiplexed into the high frequency band of the luminance signal, some problems occur in transmission. In order to solve these problems, color TV signal transmission has been considered in which the color signal is compressed in the time axis and multiplexed in the horizontal blanking period of the luminance signal. 1st
The figure is an explanatory diagram of the transmission form of this color TV signal transmission system. A is a waveform diagram of a certain portion of the video signal, and b is a signal waveform diagram of a vertical blanking portion.
In FIG. 1A, in the composite video signal, a burst signal indicating horizontal synchronization is inserted within a certain section of each horizontal scanning period, and is superimposed with the same phase in each horizontal scanning period. The luminance signal is inverted (Y/-Y) every 1H line. 1H line color difference signal R-Y
and B-Y are compressed and inserted alternately into the horizontal blanking portion every one scanning period, and have different polarities every two scanning periods. (C _W , C _N , −C _W , −C _N ,
_CW ……. ) Also, the audio signal is a burst signal,
Immediately afterwards, it is AMI encoded at a bit rate twice the burst signal frequency and superimposed.

In b, the vertical synchronization burst signal (which has the same frequency and phase as the burst signal indicating the horizontal synchronization position) is superimposed for each frame.

In order to generate a continuous master clock in synchronization with the transmitter's clock in the receiver, a burst signal indicating the horizontal synchronization signal position is extracted from the composite video signal, and this burst signal is combined with the internal oscillator. can be obtained by phase locking. To extract a burst signal, from the viewpoint that there is a correlation between images in lines before and after one scan, a comb filter that takes line correlation with a 1H delay line is used to extract image components (frequencies other than burst signal components) within one scan period. The frequency components of the burst signal can be emphasized and extracted. In other words, when delaying the previous line signal and performing correlation comparison with the next line, the phase of the previous line signal is adjusted by 180°.
When inverted and correlated, the luminance signal Y becomes -Y after a delay of 1H, and in comparison with the luminance signal Y of the next line, Y+(-Y)=0. FIG. 2 shows a conventional configuration block diagram.

1 is a band pass filter (BPF), 2 is an automatic gain control circuit (AGC), 3 is a comb filter,
4 is a peak detector, 5 is a DC amplifier, 6 is a phase comparator, 7 is an oscillator, 8 is a frequency divider, 9 is an input terminal,
10 is an output terminal. The composite video signal explained in FIG. 1 is input to the input terminal 9. From the input composite video signal, a frequency component of a burst signal is extracted by a BPF 1, and a comb filter 3 via an AGC 2 extracts a burst frequency signal component from which a luminance signal component has been removed. The peak detector 4 detects the peak value of the output signal of the comb filter 3 and controls the AGC 2 via the DC amplifier 5 to keep the amplitude of the output of the comb filter 3 constant.

The output of this comb filter 3 is sent to a phase comparator 6.
A frequency divider 8 which divides the signal of the oscillator 7 by n
The frequency of the oscillator 7 is controlled by the output of the comparison difference, and a continuous clock pulse signal synchronized with the burst frequency signal is obtained as the output of the frequency divider 8.

However, with such a simple configuration, the audio signal can be transmitted at twice the frequency of the burst signal.
Because the audio signal is AMI encoded and superimposed within the horizontal scanning period, and the audio signal has no correlation with the previous line, the output of the comb filter 3 is as follows:
The signal components are superimposed to form a signal waveform as shown in Fig. 3, and when this signal is input to the phase comparator 6, the phase comparison difference output will cause slight level fluctuations due to these effects, and Jitter occurs in the output signal of frequency generator 8. Therefore, it was not possible to obtain a stable master clock signal.

Purpose of the Invention In view of these points, the present invention completely eliminates the influence of signal components such as luminance signals, color difference signals, and audio signals from a composite video signal in which a burst signal is superimposed on a fixed interval indicating a horizontal synchronization position. It is an object of the present invention to provide a clock signal generation device which generates a master clock signal synchronized with a stable horizontal synchronization burst signal without jitter.

Structure of the Invention The present invention removes signal parts such as a luminance signal, a color difference signal, and an audio signal included in one line from a composite video signal in which a burst signal is superimposed in one fixed interval indicating a horizontal synchronization position, and horizontal synchronization is performed. By supplying a signal obtained by gating only the burst signal portion to the phase comparator, the influence of these components is eliminated and a stable clock signal can be obtained.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. FIG. 4 is a block diagram of a clock signal generator according to an embodiment of the present invention, and FIG. 5 is a timing chart illustrating the operation of the embodiment. In Fig. 4, 1 is a bandpass filter (BPF) that passes a signal in the burst signal frequency band from a composite video signal in which a burst signal is superimposed in one fixed interval indicating the horizontal synchronization position, and 2 is a band pass filter (BPF) that passes a signal in the burst signal frequency band. 3 is an automatic gain control circuit (AGC) that keeps the amplitude of the signal constant; 3 is a comb filter with a 1H delay configuration that extracts the burst frequency signal component from which the luminance signal component and color difference signal component have been removed from the signal detected by BPF1; 4 5 is a peak detector that detects the peak of the burst frequency signal obtained by the comb filter 3 and holds the voltage value; 5 is a DC amplifier that controls the output gain of the AGC 2 based on the voltage held by the peak detector 4; 6 is a DC amplifier that controls the output gain of the AGC 2 using the voltage held by the peak detector 4; Oscillator 7
The phase comparator and oscillator 7 compare the frequency-divided signal from the burst frequency signal obtained through the BPF 1, AGC 2, comb filter 3, and gate circuit (1) 18, and output the frequency difference as a voltage. It oscillates continuously around a frequency n times the burst frequency, and is slightly controlled by the output of the phase comparator 6. 8 is a frequency divider that divides the signal of the oscillator 7 (1/n); 9 is an input terminal for a composite video signal; 10 is an output terminal for a clock signal; A binarizing waveform shaper 12 outputs the required horizontal synchronization frequency from each frequency dividing terminal of the horizontal synchronization period frequency divider 14 to the continuous pulse frequency synchronized with the burst frequency signal obtained by the frequency divider 8. The gate circuit (2), 13 which takes out the divided pulses less than the frequency division ratio is a set-up circuit that operates with the frequency of the gate circuit (2) 12 and the output of the waveform shaper 11.
Reset type flip-flop, 14 is frequency divider 8
This is a horizontal synchronization period frequency divider which divides the frequency from the output pulse of 1 to the horizontal synchronization period, and its counting operation is controlled by a signal from the flip-flop 13. 15 is a matrix circuit that generates pulses from each frequency dividing terminal of the horizontal synchronization cycle frequency divider 14 at the leading edge position and the trailing edge position of the horizontal synchronization burst frequency signal obtained by the comb filter 3; 16 is a matrix circuit; A set/reset type flip-flop operates on each output of the circuit 15; 17 denotes a pulse generation circuit consisting of the matrix circuit 15 and the flip-flop 16; Generates a pulse that turns on at the trailing edge position and turns off at the trailing edge position. 1
8 is the output of the comb filter 3, and the pulse generation circuit 1
This is a gate circuit (1) which gates by the output of 7 and supplies it to the phase comparator 6.

Next, the operation of this device will be explained using the timing chart shown in FIG.

A is a composite video signal input to the input terminal 9, which is the same signal as in FIG.

The input composite video signal (a) is BPF1, AGC
The comb filter 3 outputs a signal in which the audio signal component is superimposed on the horizontal synchronization burst signal (b) from which the luminance signal component and color difference signal component are removed through the comb filter 2 and the comb filter 3. From the output of comb filter 3,
The peak value of the horizontal synchronous burst frequency signal is held by the peak detector 4, and the AGC 2 is controlled via the DC amplifier 5, so that the output of the comb filter 3 always maintains a constant amplitude despite amplitude fluctuations of the input signal. Make it.

The output of this comb filter 3 is processed by a waveform shaper 11.
is input to the waveform shaper 11 and sliced at a constant level (broken line shown in waveform (b)) to obtain a binarized signal c. This binary signal C is input to the set terminal of the flip-flop 13 of the set/reset type, and the required horizontal synchronous frequency is inputted to the other reset terminal from each frequency dividing terminal of the horizontal synchronous period frequency divider 14. Divided pulse less than the division ratio (d)
is input via the gate circuit (2) 12. The output (E) of the flip-flop 13 is input to the reset terminal of the horizontal synchronization frequency divider 14, and the divided pulse position is set to a value smaller than the division ratio of the required horizontal synchronization frequency.
By stopping the count at (D) and then starting the count at the first pulse position of the binarized signal (C) obtained by the waveform shaper 11, the horizontal The phase relationship with the synchronization signal (burst signal position) is matched.

In addition, each frequency dividing terminal of the frequency divider 14 for horizontal synchronization period is inputted to the matrix circuit 15, and the start position (f) and end position of the horizontal synchronization burst frequency signal of the output signal (b) obtained from the comb filter 3 are input. Pulses are generated at positions (Y), and their respective outputs are input to a set/reset type flip-flop 16 to generate gate pulses (H).

This gate pulse (H) is supplied to the gate circuit (1) 18 and is a horizontal synchronization burst frequency obtained by gating the output signal from the comb filter 3 to remove components such as a luminance signal component, a color difference signal component, and an audio signal component. Gate circuit (1)1
We get an output of 8.

The output of the gate circuit (1) 18 is input to one side of the phase comparator 6, and is compared with the pulse frequency from the frequency divider 8. The output of the phase comparator 6 controls the oscillator 7, and the frequency is divided. At the output of the circuit 8, a stable and continuous clock pulse signal without jitter can be obtained.

Effects of the Invention As described above, according to the present invention, luminance signal components, color difference signal components, audio signal components, etc. included in one line are extracted from a composite video signal in which a burst signal is superimposed on one fixed interval indicating a horizontal synchronization position. To provide a clock signal generation device which generates a stable continuous clock signal without jitter by eliminating the influence of those components and inputting a signal obtained by gated only horizontal synchronization burst signals to a phase comparator. The practical effect is great.

[Brief explanation of drawings]

Fig. 1 is a waveform diagram of a composite video signal in a color television transmission format, Fig. 2 is a block diagram of a conventional device that generates a clock signal from the composite video signal of Fig. 1, and Fig. 3 is a problem that occurs in the same device. FIG. 4 is a block diagram of a clock signal generator according to an embodiment of the present invention, and FIG. 5 is a waveform diagram for explaining the points.
This figure is a timing chart for explaining the operation of the clock signal generator shown in FIG. 4. 1... Filter, 2... Automatic gain control circuit, 3
... Comb filter, 6 ... Phase comparator, 7 ... Oscillator, 8 ... Frequency divider, 11 ... Waveform shaper, 12
...Gate circuit (2), 13...Flip-flop,
14...Horizontal synchronization cycle frequency divider, 17...Pulse generation circuit, 18...Gate circuit (1).

Claims (1)

[Claims] 1. A system that generates a continuous wave clock signal synchronized with the burst signal from a composite video signal in which a burst signal is superimposed on a certain section indicating a horizontal synchronization position, and a filter that detects only the frequency component of the burst signal. an automatic gain control circuit that keeps the amplitude of the detected burst signal constant; a waveform shaper that binarizes the burst signal; a gate circuit that gates the detected burst signal; a phase comparator that locks the frequency of continuous pulses; an oscillator whose phase is locked by the phase comparator to generate continuous pulses and whose output is used as a clock signal; and a horizontal synchronization period that divides the frequency of the continuous pulses of the oscillator. The horizontal synchronization cycle frequency divider is controlled in synchronization with the position of the burst signal every scanning cycle by outputs from the waveform shaper and the horizontal synchronization cycle frequency divider. and a pulse generation circuit for operating the gate circuit from the horizontal synchronization period frequency divider, the pulse generation circuit detects the horizontal synchronization period in the period of the horizontal synchronization burst signal output detected by the filter. A gate pulse having a rising edge determined by a circuit controlling the frequency divider and a pulse width determined by the pulse generating circuit is generated, and the gate pulse is generated only in the horizontal synchronization burst signal section by the gate circuit. A clock signal generation device characterized in that a gated signal is input to the phase comparator.