JPH0417505B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a horizontal synchronization detection device for a receiver in color TV signal transmission. It is detected from the composite video signal.

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 in broadcasting etc. converts color signals into high-frequency luminance signals. Frequency multiplexing into bands creates some transmission problems. In order to solve these problems, studies are being conducted on color TV signal transmission in which the color signal is compressed in the time axis and multiplexed in the horizontal blanking period of the luminance signal.

Traditionally, the horizontal synchronization signal in these transmissions is
This is a method in which pulses of a constant width are superimposed within the blanking section of the video signal, and the transmission form described below was used.

FIG. 1 is a composite video signal waveform diagram showing a conventional transmission form. H is a horizontal synchronizing signal whose polarity differs every scanning period (1H line). R-Y and B-Y compress the 1H line color difference signal and are inserted alternately into the horizontal blanking portion every one scanning period, and have different polarities every two scanning periods.

Y is a luminance signal, and this luminance signal is a signal whose polarity is inverted for each line. This composite video signal is transmitted to a receiver.

Therefore, since the horizontal synchronization signal H is bipolar, the horizontal synchronization detection method of the receiver is ±V shown in the figure.
, the composite video signal is sliced to obtain positive and negative polarity synchronization signals, respectively, and then an ordinary synchronization signal (Fig. 1,
synchronization detection output).

According to the conventional transmission form, in synchronization detection,
Slight jitter occurs in the time axis direction due to transmission distortion in the transmission line, level fluctuations, etc., making it difficult to obtain a synchronized signal with accurate and reliable precision, and being susceptible to transmission line noise.These problems have been solved. This had the disadvantage that the circuit became complicated.

In order to eliminate the above-mentioned drawbacks, the present invention
A new transmission form that inserts the highest brightness image frequency (burst signal) within a fixed interval that indicates the horizontal synchronization signal position, detects only this burst signal, is stable, highly accurate, resistant to transmission noise, and has a simple circuit configuration. The present invention provides a horizontal synchronization detection device.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a composite video signal waveform diagram of the new transmission form, where a is a waveform diagram spanning several H lines, and b is an enlarged diagram of 1H line. Figure 3 shows
FIG. 4 is a block diagram of a horizontal synchronization detection device which is an embodiment of the present invention, and is a timing chart for explaining the operation of the embodiment. The format of the transmitted color TV signal, as shown in Figure 2a, is a burst signal with the same phase for every H line indicating a horizontal synchronization signal, and a luminance signal -Y/Y that is inverted for every 1H line. , compressed color difference signals R-Y, B-
Y is made up of signals whose polarity is inverted alternately every 1H line and whose polarity is inverted every 2H lines. Second
Figure b is an enlarged view of 1H of the horizontal scanning period of a.
No-signal areas (guards) are provided between the burst signal and the luminance signal -Y, between the luminance signal -Y and the color difference signal RY, and between the color difference signal RY and the next burst signal.

In Fig. 3, 1 is a band pass filter (hereinafter abbreviated as BPF), 2 is an automatic gain control circuit (hereinafter abbreviated as AGC circuit), 3 is a comb filter with a 1H delay, 4 is a peak detector, and 5 is an AGC circuit 2 DC amplifier that controls and drives the gain of
6 is a phase comparator, 7 is a VCO, 8 and 9 are frequency dividers, 10 is a logarithmic amplifier circuit, 11 is a comparator, 12 is a set/reset type flip-flop, 1
3 is a gate circuit, 14 is a matrix circuit for extracting arbitrary position pulses from each divided output of the frequency divider 9, 15 is a set/reset type flip-flop, 16 is an input terminal for the composite video signal shown in FIG. 17 is a clock output terminal, and 18 is a horizontal synchronization signal output terminal.

Here, the frequency divider 9 is composed of a counter, and this frequency divider 9 and a gate circuit 13 that decodes the output of this frequency divider 9 create a pulse having a division period slightly shorter than the horizontal synchronization period. It constitutes frequency dividing means.

Next, the operation of this device will be explained using the timing chart of FIG. FIG. 4A is the same signal as in FIG. 2 that is input to the input terminal 16 of the present invention. The input signal A is input to the BPF 1 which passes the burst signal frequency band, and this burst signal is detected to obtain a signal B from which the luminance signal component and the color difference signal component are substantially removed.

The output of the BPF 1 is inputted via the AGC circuit 2 to a comb filter 3 having a 1H delay configuration.

From the viewpoint that there is a correlation between images in the lines before and after one scan, by taking the line correlation with this 1H delay, the image components (frequency other than the burst component) within one scan period become -Y+Y=0. Since the burst frequency signal is attenuated and has the same phase, only this signal is emphasized, and a burst frequency signal C with a good S/N ratio can be obtained. D is an enlarged waveform diagram of one scanning period of C. The output of the comb filter 3 is input to a phase comparator 6, a peak detector 4, and a logarithmic amplifier circuit 10, respectively.

The peak detector 4 detects the peak point of the burst frequency signal and holds the voltage value (indicated by a dotted line in waveform 2).
Driven by DC amplifier 5, AGC circuit 2
Controls the output gain of

From the above, the amplitude is always kept constant at point A in FIG. 3 despite the amplitude fluctuation of the input signal.

On the other hand, the output of the comb filter 3 is output to the phase comparator 6.
, the output of comb filter 3 and the oscillator
The phase is compared with the output obtained from the VCO 7 (which oscillates at a frequency n times the burst frequency) through the frequency divider 8 which divides it by 1/n, and the comparison difference output is used to generate the oscillator 7.
The continuous burst signal frequency locked to the burst frequency is obtained at the output of the frequency divider 8. Further, the output of the frequency divider 8 is inputted to the clock output terminal 17 and the frequency divider 9.

The output of the frequency divider 8 operates the frequency divider 9, and the matrix circuit 14 and the set/reset flip-flop circuit 15 generate horizontal synchronizing signals from each binary output of the frequency divider 9.
In this case, the frequency divider 9 performs free-running counting, so the composite video signal sent from the transmitting side (Fig. 4 A)
does not match the horizontal synchronization signal (burst signal position).

Therefore, it is necessary to extract the burst signal position of the composite video signal and control the phase of the frequency divider 9.

To extract the burst signal position, the amplitude is made constant by the AGC circuit, and the output signal of the comb filter 3 from which only this burst frequency signal is extracted is converted into a binary value. If the output of the comb-shaped filter 3 is directly converted into a binary value, as shown in Fig. 4D, the potential difference β between one cycle is small, so it is converted into a binary value at different cycle positions depending on power supply voltage fluctuations, etc. is,
This causes jitter in the time axis direction.

Therefore, the logarithmic amplifier circuit 10, which converts the input voltage into a logarithmic output voltage, converts the input voltage into a signal voltage at which the maximum potential difference a occurs for a certain input level, as shown in FIG. In this case, although linear amplification that maximizes the potential difference a is possible, non-linear amplification can reduce malfunctions. Thereafter, the comparator 11 binarizes at a slice level set at the center within the potential difference a. This output waveform is shown in G.
That is, the logarithmic amplifier circuit 10 and the comparator 11 constitute a waveform shaper.

The binary output of the comparator 11 is input to a set/reset flip-flop 12. The set/reset flip-flop 12 is operated by the output of the gate circuit 13 which generates a pulse from the frequency divider 9 at a timing shorter than the horizontal synchronization period, and the output of the comparator 11. 9
input to the reset terminal.

This is to prevent malfunctions when spike noise is mixed into the composite video signal in the transmission line.In reality, most of it is removed by the comb filter 3, etc., but the output of the comparator 11 When inputting directly to the reset terminal of the frequency divider 9, for example, if noise is mixed in as shown in the dotted circle in FIG. 4, the frequency divider 9 will be reset at that point and malfunction. Therefore, a method is adopted in which the burst signal position is detected for each line. That is, from each binary counter output of the frequency divider 9, a divided pulse that is one clock less than the division ratio between the clock frequency H and the horizontal synchronization frequency is extracted from the gate circuit 13, and the set/reset flip-flop 12 is reset. When input to the terminal,
The output of the set/reset flip-flop 12 becomes "L" level, and the frequency divider 9 stops counting.

As described above, the frequency divider 9 and the gate circuit 13 constitute a frequency dividing means for counting continuous pulses to obtain a frequency division pulse slightly shorter than the horizontal synchronization period.

Next, comparator 1 which took out the horizontal synchronization signal position
When the output of 1 is input to the set terminal of the set/reset flip-flop 12, the output of the set/reset flip-flop 12 becomes "H" level, and the frequency divider 9 starts counting.

Therefore, from the division ratio between the clock frequency and the horizontal synchronization frequency extracted by the gate circuit 13,
The frequency divider 9 operates itself during the frequency division period where the frequency is reduced by one clock, and when this period ends, the frequency divider 9 is reset once and starts counting again from the leading edge pulse of the burst signal position that occurs one clock later. Start. From the above, it is possible to completely match the phase relationship between the composite video signal sent from the transmitting side and the horizontal synchronization signal (burst signal position).

Furthermore, even if the noise indicated by the dotted circle in FIG.

As described above, a horizontal synchronization signal can be obtained from the output signal of the flip-flop 12 obtained by the signal from the frequency dividing means and the waveform shaper, but a horizontal synchronization signal can also be obtained at an arbitrary position in the horizontal synchronization period. In order to do this, the binary counter outputs of the frequency divider 9 with the same phase relationship are inputted to the matrix circuit 14, and the starting position and ending position of the horizontal synchronization signal to be generated at an arbitrary position are generated, respectively. By inputting the signals to the set and reset flip-flops 15, another horizontal synchronizing signal can be obtained.

As described above, the present invention provides horizontal synchronization that is stable, highly accurate, resistant to transmission noise, and has a simple circuit configuration in a new transmission form in which a burst signal of the highest image frequency is inserted within one fixed interval indicating the horizontal synchronization signal position. It is a detection device.

[Brief explanation of drawings]

Figure 1 is a composite video signal waveform diagram in a conventional transmission format, Figure 2 is a composite video signal waveform diagram in a new transmission format that compensates for the drawbacks of the conventional method, and Figure 3 is an embodiment of the present invention based on the transmission format shown in Figure 2. FIG. 4 is a timing chart for explaining the operation of the synchronization detection device shown in FIG. 1... Filter, 2... Automatic gain control circuit, 3
... Comb filter, 6 ... Phase comparator, 7 ... Oscillator, 9 ... Frequency divider, 10 ... Logarithmic amplifier, 11
...Comparator, 12...Flip-flop, 13...
...Gate circuit.

Claims (1)

[Claims] 1 A device for detecting a horizontal synchronization signal from a composite video signal in which a burst signal is superimposed on a certain interval indicating a horizontal synchronization position, which comprises a filter for detecting only the frequency component of the burst signal, and a filter for detecting only the frequency component of the burst signal. an automatic gain control circuit that keeps the amplitude constant; a phase comparator that locks the frequency of the burst signal from the automatic gain control circuit with the frequency of an internal oscillator; It includes an oscillator that generates pulses, a waveform shaper that binarizes the burst signal from the automatic gain control circuit, and a counter that counts the continuous pulses. A frequency dividing means for generating a frequency division pulse having a short frequency division cycle is provided, and the frequency division means is set by the output of the waveform shaper, reset by the frequency division pulse, and decodes the output of the counter. A horizontal synchronization detection device characterized by obtaining a horizontal synchronization signal.