JPH0417506B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention inserts a burst signal into a normal television signal within a certain interval indicating the position of the horizontal synchronization signal and at the beginning of a frame indicating the vertical synchronization, and extracts the horizontal synchronization signal from the transmitted composite video signal. It is something to detect.

In recent years, with the spread of image transmission services such as ITV, there has been an increasing demand for colorization of images, but the color transmission system (NTSC system) used in broadcasting etc. transfers color signals to the high frequency band of luminance signals. Frequency multiplexing causes some transmission problems. In order to solve these problems, studies are being conducted on color TV signal transmission in which the color signal is time-base compressed and multiplexed during the horizontal blanking period of the luminance signal.

FIG. 1 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 of a vertical blanking portion. In a, in the composite video signal, a burst signal indicating horizontal synchronization is inserted within one fixed interval of each horizontal scanning period, and 0 phase and π phase are alternately superimposed in each horizontal scanning period. Y is a luminance signal of 1
The polarity becomes the same every scanning period. CW・CN
is the compressed color difference signal, CW is the RY signal,
CN is a BY signal. This color difference signal CW, CN
The R-Y and B-Y signals are alternately extracted every two horizontal scanning periods, and each is compressed and superimposed after the luminance signal Y. b shows the first and second field portions of the vertical blanking period. As shown in the figure, a vertical synchronization burst signal is transmitted every frame (same as the burst signal frequency indicating the horizontal synchronization position, and the phase is 0 phase).
are superimposed. In addition, the television signal is
Usually, one frame ends with an odd number of lines, such as 525 or 1125 lines. Therefore, since the burst signal indicating the horizontal synchronization signal position is superimposed with alternating phases in each horizontal scanning period, the burst signal at the end of the second field (1125th) as shown in Figure 1b. The horizontal burst signal phase and the horizontal burst signal phase at the beginning (first) of the first field are in phase. As a method of extracting the burst signal indicating the horizontal synchronization signal position from the composite video signal, from the viewpoint that there is a correlation between the images in the lines before and after one scan, the burst signal is extracted from the burst band using a bandpass filter (BPF). By extracting the frequency of It can be highlighted and taken out. In other words, when the signal of the previous line is delayed and the correlation is compared with the next line, if the phase of the previous line signal is inverted by 180° and the correlation is taken, 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.
However, for burst signals, on the contrary, each line
Since the phase is reversed by 180°, the burst signal component becomes in-phase after a 1H delay, and this burst signal component is emphasized and the S/N is
Only burst frequency signals with good stable amplitude can be extracted.

However, when the burst signal is extracted by the method described above, there is a burst signal in the same phase at the frame switching point explained in Figure 1b, so from the time constant of the automatic gain control voltage, as shown in Figure 2. At the output of the comb-shaped filter, the amplitude of the burst signal after the in-phase burst signal is several H.
Over time, a phenomenon occurs where the level changes and then returns to the original level. In order to obtain a horizontal synchronization signal from this signal, it is generally sliced at a certain level and binarized to obtain a horizontal synchronization signal, but since the amplitude is not constant in the above-mentioned section, detection becomes impossible. Unable to obtain constant cycle synchronization. There is also binarization using the floating method, but in this case, the vertical synchronization burst signal inserted at the beginning of the frame is detected, resulting in false detection as above, and stable horizontal synchronization with a constant period is detected. can't get it.

In view of these points, it is an object of the present invention to provide a horizontal synchronization signal generation device that generates a stable horizontal synchronization signal with a constant period using a novel synchronization generation method.

The present invention will be explained in detail below. FIG. 3 is a block diagram of a horizontal synchronizing signal generator according to an embodiment of the present invention, and FIG. 4 is a timing chart for explaining the operation of the embodiment. In Fig. 3, 1 is a band pass filter (BPF) that passes signals in the burst signal frequency band from a composite video signal in which a burst signal is superimposed on a certain interval indicating the horizontal synchronization position, and 2 is a band pass filter (BPF) that passes the burst signal from the output of BPF 1. 3 is a comb filter with a 1H delay configuration that extracts only the burst frequency signal 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, and 5 is a DC amplifier that controls the output gain of the AGC circuit 2 using the voltage held by the peak detector 4. , 6 divides the burst frequency signal extracted by the comb filter 3 into a frequency divider 1.
A switch that converts the phase polarity of the burst frequency signal using a switching pulse from 9 that is inverted every 1H (one scanning period). A phase comparator and oscillator (VCO) 8 that compares the burst frequency signal obtained through the switch 6 and outputs the frequency difference as a voltage continuously oscillates around a frequency that is n times the burst frequency, and performs phase comparison. It is slightly controlled by the output of device 7. 9 is a frequency divider that divides the signal of the oscillator 8 (1/n); 10 is a horizontal synchronization signal generation frequency divider that divides the frequency from the output pulse of the frequency divider 9 to the horizontal synchronization period; The counting operation is controlled by a signal from the switch 21. 11 is a horizontal synchronization signal generation frequency divider 1
12 is a matrix circuit that generates pulses at the start and end positions of the horizontal synchronization signal to be generated from each frequency dividing terminal of 0; 12 decodes the output of the horizontal synchronization signal generation frequency divider 10; The gate circuits 1 and 23 extract a divided pulse smaller than the required horizontal synchronization frequency division ratio from the continuous pulse frequency synchronized with the burst frequency signal obtained in step 9, which is the output of the horizontal synchronization signal generation frequency divider 10. This is a gate circuit 2 that decodes the continuous pulse frequency synchronized with the burst frequency signal obtained by the frequency divider 9 and extracts a frequency-divided pulse consisting of a required horizontal synchronization frequency division ratio, and generates a horizontal synchronization signal. Frequency divider 1
0, gate circuits 1, 12 and gate circuits 2, 23
constitutes a frequency dividing means. 13 is a double-wave rectifier that double-wave rectifies the signal from the comb filter 3; 14 is a logarithmic amplifier that generates an output voltage having a logarithmic characteristic for the output signal of the double-wave rectifier 13; 15 is the output signal of the logarithmic amplifier 14; A comparator that binarizes at a certain level; 16 is a set-reset flip-flop operated by gate circuits 1 and 12 and a switch 21; 17 is a low-pass filter that extracts a vertical synchronization burst signal from the composite video signal of AGC 2, etc. 18 is a comparator that converts the signal detected by the vertical burst detector 17 into a binary level; 19 is a vertical burst detector 17 that detects the vertical burst signal; A frequency divider which operates with the converted vertical pulse signal and the horizontal periodic pulse signal from the matrix circuit 11 and divides this horizontal synchronization by 1/2; 21 is a signal from the pulse generator 20, which selects the signals from the flip-flop 16 and the gate circuits 2 and 13, and supplies the selected signal to the frequency divider 10 for horizontal synchronization signal generation. , 22 is a flip-flop which operates with pulses at the start and end positions of the horizontal synchronization signal obtained by the matrix circuit 11 and generates a horizontal synchronization signal, 24 is an input terminal for the composite video signal, 25 is a phase comparator 7, An output terminal 26 outputs a continuous pulse frequency synchronized with the burst frequency signal obtained by the oscillator 8 and the frequency divider 9;

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 24, which is the same signal as in FIG. The input composite video signal is BPF1
As a result, a signal B of the burst signal frequency component is extracted, and a signal C is generated in which only the burst frequency signal from which the luminance signal component and the color difference signal component have been removed is extracted by the comb filter 3 via the AGC circuit 2. From the output of the comb filter 3, a peak detector 4 holds the peak value (indicated by a broken line) of the burst frequency signal C, and controls the AGC circuit 2 via the DC amplifier 5 to compensate for amplitude fluctuations in the input signal. On the other hand, the output of the comb filter 3 always has a constant amplitude.

Further, from the output of the AGC circuit 2, a vertical burst detector 17 generates a signal D with high frequency components removed, and a comparator 18 generates a vertical pulse signal H which is sliced at a constant level at which no horizontal burst signal is detected. get. This vertical pulse signal is supplied to a frequency divider 19 and a pulse generator 20. From the falling edge of the vertical pulse signal E, the pulse generator 20
is operated, and the output of the comb filter 3 causes an amplitude change at the beginning of the frame explained in FIG.
A pulse is generated over a number H (for example, 1 to 6 pulses) as shown in FIG.

The frequency divider 19 is also operated with a pulse generated approximately at the center between the burst signals indicating the horizontal periodic signal from the matrix circuit 11, and generates a signal whose frequency is divided by 1/2. The frequency divider 19 is reset by the vertical pulse signal E from the comparator 18, so that each frame is output in the same phase. Therefore, as shown in G at the end and beginning of the frame,
High level occurs over 2 hours. The output of the frequency divider 19 operates the switch 6 to switch the polarity of the burst frequency signal for each H, so that the output of the switch 6 is in phase for each H. . A phase comparator 7 compares the output of the switch 6 and the output of a frequency divider 9 that divides the signal of the oscillator (V-CO) 8 by 1/n, and the frequency of the oscillator 8 is controlled by the output of the comparison difference. A continuous burst frequency signal chain locked to the frequency signal is obtained at the output of the frequency divider 9. The output of this frequency divider 9 is input to an output terminal 25 and a horizontal synchronization signal generation frequency divider 10. On the other hand, the output of the comb filter 3 is input to a double-wave rectifier 13, converted into an output voltage in the same direction, and input to a logarithmic amplifier 14. A logarithmic amplifier 14 converts the signal with the greatest potential difference to a certain input level, and a comparator 15 converts the signal where the potential difference occurs.
A binarized signal is obtained by slicing at a constant level set at .

This is because the phase of the input burst signal is inverted for each line, so if only one wave is binarized, a half-clock shift will occur for each line, and this will cause the horizontal synchronization signal to be generated. This is to prevent the frequency divider 10 from malfunctioning. This binary signal is input to the set terminal of the flip-flop 16 of the set/reset type, and the required horizontal A divided pulse number smaller than the synchronous frequency division ratio is input through the gate circuit 1, and the flip-flop 1
The output of 6, that is, the synchronization signal L, is supplied to a switch 21. In addition, a frequency divider 10 for generating a horizontal synchronizing signal
The gate circuit 2 generates a frequency division pulse having a required frequency division ratio of the horizontal synchronization frequency from each frequency division terminal, and supplies it to the switch 21. This switch 2
1, during the high level period of the pulse from the pulse generator 20, the output pin of the flip-flop 16 synchronized with the burst signal is connected to the reset terminal of the horizontal synchronization signal generation frequency divider 10, and during the low level period, A signal synthesized to supply the output of the gate circuit 2, that is, the horizontal synchronization signal O, extracted from the horizontal synchronization signal generation frequency divider 10 at a division ratio of the horizontal synchronization frequency to the reset terminal of the horizontal synchronization signal generation frequency divider 10. The phase relationship of the frequency divider 10 for generating the horizontal synchronizing signal is controlled by generating the frequency divider 10.

By controlling as described above, a horizontal synchronizing signal can be obtained from the output of the gate circuits 2 and 23. However, in order to obtain a horizontal synchronizing signal at any position within the horizontal synchronizing period, this horizontal synchronizing signal generation is necessary. The frequency divider terminals of the frequency divider 10 are inputted to the matrix circuit 11, and the start and end positions of the horizontal synchronization signal to be generated at an arbitrary position are generated respectively, and a set-reset type flip-flop is generated. By inputting the signal to the flop 22, it is possible to obtain a stable horizontal synchronizing signal at any position with a constant period. As mentioned above, from the transmitted composite video signal
BPF/AGC, a comb filter extracts only the burst frequency signal, and from a signal obtained by binarizing this burst frequency signal at a certain level and continuous pulses synchronized with the burst frequency signal, the frequency is divided to the horizontal synchronization period. Vertical synchronization is performed by operating a flip-flop with a signal obtained from a frequency divider that is less than the division ratio of the horizontal synchronization frequency, and a signal obtained from the frequency divider with a division ratio of the regular horizontal synchronization frequency. A signal with a width of several H (the time it takes for the amplitude disturbance of the burst frequency signal at the comb filter output that occurs when switching frames to stabilize) obtained from the burst signal. By switching to a frequency division signal consisting of the division ratio of the horizontal synchronization frequency and controlling the count of this frequency divider, jitter-free synchronization with the burst signal can be achieved.
A stable horizontal synchronization signal with a constant period can be obtained.

As described above, the present invention extracts a burst signal from a composite video signal in which a burst signal is inserted within a certain interval indicating the horizontal synchronization signal position and at the beginning of a frame indicating vertical synchronization, thereby achieving stable horizontal synchronization without jitter. It provides a signal generator,
The practical effects are significant.

[Brief explanation of drawings]

Fig. 1 is a waveform diagram of a composite video signal in a color TV transmission mode, Fig. 2 is a waveform diagram illustrating problems in comb filter extraction that occur in the vertical blanking part of the composite video signal of Fig. 1, and Fig. FIG. 4 is a block diagram of a horizontal synchronizing signal generating device according to an embodiment of the present invention, and FIG. 4 is a timing chart for explaining the operation of the horizontal synchronizing signal generating device in FIG. 3... Comb filter, 8... Oscillator, 10...
Horizontal synchronization frequency divider, 13...Double wave rectifier, 14...
...Anti-logarithmic amplifier, 17...Vertical burst detector,
18... Comparator, 20... Pulse generator.

Claims (1)

[Claims] 1. A burst signal is superimposed on one fixed interval indicating the horizontal synchronization position and the phase is inverted every fixed interval, and the phase of the horizontal burst signal at the end of the second field and the one field are further superimposed. A device for detecting a horizontal synchronizing signal from a composite video signal having the same phase as a horizontal burst signal at the beginning of an eye, the device comprising: a comb-shaped filter that detects only the frequency component of the burst signal; and a comb filter that detects only the frequency component of the burst signal; an automatic gain circuit that keeps the output constant; a switch that converts the burst signal output controlled by the automatic gain circuit into a burst signal of the same phase; and a switch that locks the frequency of the burst signal of the same phase and the frequency of the continuous pulse. an oscillator whose phase is locked by the phase comparator to generate the continuous pulse; a waveform shaper which converts the burst signal output controlled by the automatic gain circuit into a binary signal; It is equipped with a vertical pulse generator that detects a vertical synchronization burst signal from a composite video signal and generates a pulse of a certain period, and a counter that counts the continuous pulses.The output of this counter is decoded and divided into a frequency slightly shorter than the horizontal synchronization period. a frequency dividing means for generating a first frequency divided pulse having a period and a second frequency divided pulse having the same frequency division period as the horizontal synchronization period; and an output of the waveform shaper set by the first frequency divided pulse; and switching means for switching the output of the flip-flop means and the second divided pulse output by the output of the vertical pulse generator, and the frequency dividing means is configured to switch between the output of the flip-flop means and the second divided pulse output by the output of the vertical pulse generator. Set by rising and falling (or falling and rising) of
1. A horizontal synchronizing signal generating device, wherein the horizontal synchronizing signal generating device is reset and decodes the output of the counter to generate a horizontal synchronizing signal.