JPH0113269B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a burst detection synchronization method used to synchronize signals such as high-definition television (TV) signals where burst signals are synchronization signals. be.

Configuration of conventional example and its problems FIG. 1 shows a conventional burst detection synchronization circuit. The configuration of this conventional example will be explained below with reference to FIG. 1. In FIG. 1, 1 is a band filter, and this band filter 1 has an input signal 7.
is input. Further, the output of the bandpass filter 1 is input to subtraction circuits 2 and 4. The output of the attenuation circuit 6 is input to the other input of the subtraction circuit 2. The output of the subtraction circuit 2 is input to a delay circuit 3, and the output of the delay circuit 3 is input to the other input of the subtraction circuit 4. The output of the subtraction circuit 4 is the window comparator 5
is input to the attenuation circuit 6, and a synchronization pulse 8 is output from the window comparator 5.

Next, the operation of the above conventional example will be explained. In FIG. 1, a signal as shown in FIG. 2 is added as the input signal 7. This is a video signal in which a burst is added as a synchronizing signal, and the polarity of the burst is inverted every time. Further, the burst period is assumed to be time τ _D , which corresponds to one line of video. Assuming that the subtraction circuit 1 does not receive an input from the attenuation circuit 6, the input signal 7 is input to the delay circuit 3 as is after frequency components other than those near the burst frequency are attenuated by the bandpass filter 1. The subtraction circuit 4 takes the difference between the input and output of the delay circuit 3, but since the delay time of the delay circuit 3 is τ _D , it takes the difference from the signal just one line before. As is clear from Fig. 2, the signal from one line before the burst has opposite polarity, and the video signals have a strong correlation between lines and are almost the same signal, so in the end, the output of the subtraction circuit 4 is the video signal. It is suppressed and becomes only a burst. Further, by applying the output to the subtraction circuit 2 through the attenuation circuit 6, positive feedback is applied, and the degree of suppression of the video signal increases. The burst thus extracted has a waveform that rises slowly as shown in FIG. 3, and the polarity is reversed every time. The output of the window comparator 5 is inverted when the absolute value of the input voltage exceeds a certain value, so as shown in Figure 4c, the output of the window comparator 5 is independent of the polarity of the input (Figure 4a, b). It's a certain timing. Therefore, by using this output as the synchronization pulse 8 as a time reference, images can be synchronized. It is also possible to create a clock that is in phase with the extracted burst. However, in the first half of the conventional example, as shown in Fig. 4, there is little margin in the threshold value of the window comparator 5, so when the waveform of the input signal 7 changes due to band restriction etc., the synchronization pulse 8 is output at the peak next to the burst. There was a problem that synchronization accuracy could not be achieved.
Additionally, large and expensive components such as delay elements must be used, resulting in a high cost.

OBJECT OF THE INVENTION The present invention eliminates the problems of the conventional method described above, and aims to inexpensively realize a burst detection synchronization method that is less susceptible to changes in burst waveforms due to band limitations of transmission lines, etc. It is.

Composition of the Invention In order to achieve the above object, the present invention utilizes the fact that the number of zero-crossing points of a burst is constant, counts the zero-crossing points of a signal, detects that the number is constant, and synchronizes. This has the effect of making the time position of the zero-crossing point less susceptible to the influence of signal amplitude.

DESCRIPTION OF EMBODIMENTS The configuration of an embodiment of the present invention will be described below with reference to the drawings.

In FIG. 5, 9 is an input signal, and this input signal 9 is transmitted to a clock generator 12, a zero cross detector 10, and a peak holder 11 with both positive and negative polarities.
added to. This positive/negative peak holder 11 provides a threshold voltage to the zero cross detector 10. The output of clock generator 12 is counter 1
3 and the synchronous pulse generator 14. The output of zero-crossing detector 10 is applied to counter 13, and the output of counter 13 is applied to synchronous pulse generator 14. Synchronous pulse generator 14
The output of is the synchronization pulse 15.

Next, the operation of the above embodiment will be explained. Fifth
A signal including a burst signal as shown in FIG. 2 is added as the input signal 9 in the figure. Positive/negative peak holder 11
By holding the (+) and (-) peaks of the signal, a constant threshold value is set to the zero cross detector 10 with respect to the center level of the burst, regardless of the magnitude of the DC potential contained in the input signal 9. give. The zero-crossing detector 10 outputs a pulse when the input signal 9 crosses the center value of the burst signal of the input signal. However, as shown in FIG. 6, a pulse is output only when the input signal 9 crosses the burst center level within a certain time after exceeding the threshold value. The clock generator 12 is composed of, for example, a PLL or the like, and generates a clock having a constant phase in response to the burst of the input signal 9. The counter 13 counts the output pulses of the zero-crossing detector 10, but uses the clock from the clock generator 12 to count only the pulses that come at regular intervals. If the burst has N periods, the zero-cross detector 10 output pulses are (2N-1),
After counting (2N-1) pulses, the synchronous pulse generator 14 detects that the 2Nth pulse does not come and outputs the synchronous pulse 15. Since the clock from the clock generator 12 is output continuously, the absence of the 2Nth pulse can be detected. Since the synchronization pulse 15 is output at the end of the burst as shown in FIG. 7, synchronization can be achieved by using this pulse as the time reference for synchronization. In addition, synchronization protection can be applied using the characteristic that bursts are continuous at regular intervals, and the probability of erroneous synchronization due to video signals can be reduced.

In this example, the number of zero-crossing points is detected as a characteristic of a burst, and the time position of the zero-crossing point does not change easily even if the signal changes in waveform due to band limitation. It has the advantage of being able to output high synchronization pulses.

Effects of the Invention The present invention has the above-described configuration, and provides the following effects.

(a) Since the number of zero-crossing points, which are not easily affected by waveform changes due to band limitation, is extracted as a burst characteristic, a burst detection synchronization circuit with high accuracy against waveform changes can be realized.

(b) Large and expensive components and circuits such as delay circuits are not needed, and the realized circuit can be made smaller, lighter, and cheaper.

[Brief explanation of drawings]

Fig. 1 is a circuit block diagram implementing the conventional burst detection synchronization method, Fig. 2 is an input signal waveform diagram of the same circuit, Fig. 3 is an input waveform diagram of the window comparator of the same circuit, and Fig. 4 is a diagram of the input signal waveform of the same circuit. FIG. 5 is a block diagram of a circuit implementing the burst detection synchronization method in one embodiment of the present invention, FIG. 6 is an explanatory diagram of the operation of the zero-cross detector of the same circuit, and FIG. FIG. 3 is a timing chart for outputting synchronizing pulses of the circuit. 9...Input signal, 10...Zero cross detector,
11... Positive/negative peak holder, 12... Clock generator, 13... Counter, 14... Synchronous pulse generator, 15... Synchronous pulse.

Claims (1)

[Claims] 1. A burst detection synchronization method characterized in that when synchronizing a composite video signal using a burst signal as a synchronization signal, video synchronization is achieved by detecting that a certain number of consecutive zero-crossing points of the burst waveform occur at a certain interval. .