JPH0113268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a burst detection synchronization circuit used for synchronizing signals that use burst signals as synchronization signals, such as high-definition television (TV). It is.

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 an input signal 7 is input to this band filter 1. 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 the delay circuit 3.
The output of is input to the other input of the subtraction circuit 4.
The output of the subtraction circuit 4 is input to a window comparator 5 and an attenuation circuit 6, and the window comparator 5 outputs a synchronization pulse 8.

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 input signal 7 is a video signal to which a burst is added as a synchronization signal, and the polarity of the burst is inverted every time. Also,
It is assumed that the burst period is time τ _D , which corresponds to one line of video. Now, let's say subtraction circuit 2
Assuming that there is no input from the subtraction circuit 6, the input signal 7 is input to the delay circuit 3 as it is after having frequency components other than those near the burst frequency attenuated by the bandpass filter 1. The subtraction circuit 4 is the delay circuit 3
However, since the delay time of the delay circuit 3 is τ _D , the difference with the signal just one line before is calculated. As is clear from Figure 2, the signal from one line before the burst has the opposite polarity, and the video signal has a strong correlation between lines and is almost the same signal, so in the end, the output of the subtraction circuit 4 is suppressed by the video signal. and burst only. Furthermore,
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. Since the output of the window comparator 5 is inverted when the absolute value of the input voltage exceeds a certain value, the output of the window comparator 5 is independent of the polarity of the input signal (a, b in Fig. 4), as shown in Fig. 4c. It becomes 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 above-mentioned conventional example, all of the blocks constituting the circuit are analog circuits, and there is a problem in that level fluctuations, delay time fluctuations, etc. occur due to temperature changes and changes over time, and the timing of the synchronization pulse changes. Additionally, large and expensive components such as delay elements must be used, resulting in high costs.

OBJECTS OF THE INVENTION The present invention eliminates the problems and drawbacks of the conventional example, and aims to provide an inexpensive burst detection synchronization circuit that is stable against changes in temperature and over time.

Composition of the Invention In order to achieve the above object, the present invention digitizes most of the circuit, detects a unique pattern when a burst signal is digitized, and generates a synchronization pulse. This has the effect of increasing temperature stability and stability over time, and lowering costs.

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 input to a window comparator 10, a (+) peak hold circuit 14, and a (-) peak hold circuit 15. Further, the outputs of the (+) peak hold circuit 14 and the (-) peak hold circuit 15 are inputted to the window comparator 10 to provide a reference voltage. The output of the window comparator 10 is input to a shift register 11, the outputs of the shift register 11 and pattern generator 13 are input to a digital comparator 12, and the digital comparator 12 outputs a synchronizing pulse 16. The shift register 11 also has a clock 1 generated from the burst and in phase with the burst.
7 is input.

Next, the operation of the above embodiment will be explained. In FIG. 5, a waveform as shown in FIG. 2 is added as an input signal 9. The (+) peak hold circuit 14 and the (-) peak hold circuit 15 hold the (+) peak and (-) peak of the burst, respectively, and apply the voltages to the window comparator 10. The window comparator 10 obtains positive and negative threshold values as shown in FIG. 6a by dividing this peak voltage. This operation allows the threshold value of the window comparator 10 to be maintained at a constant level with respect to bursts even if the DC value of the video signal varies. The output of the window comparator 10 at that time is shown in FIG. 6b. Furthermore, if this output is added to the serial input of the shift register 11 and a clock 17 with a phase as shown in FIG. An alternating pattern of . This is a burst-specific pattern, so this pattern created in advance by the pattern generator 13 and the shift register 1
1 parallel output and digital comparator 1
2, the burst position can be detected using the coincidence signal as the synchronization pulse 16. Although the probability of a video signal containing the same signal as a burst is low, it is not impossible, so protection can be applied using the periodicity of the synchronization pulse to prevent false synchronization.

In this embodiment, the number of analog circuit parts is small, and there is no need to use expensive and large components such as delay elements, so that it is stable with respect to temperature and can be made inexpensive.

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

(a) Since the analog circuit part consists of only a window comparator and peak hold, temperature,
Stable against changes over time.

(b) Since large and expensive special parts such as delay elements are not used, the circuit can be made smaller and cheaper.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional burst detection synchronization circuit, Fig. 2 is a waveform diagram of a composite video signal input to the burst detection synchronization circuit, and Fig. 3 is a waveform diagram input to the window comparator in Fig. 1. FIG. 4 is an explanatory diagram of the operation of the window comparator, FIG. 5 is a block diagram of the burst detection synchronization circuit according to an embodiment of the present invention, and FIGS. 6a to 6c are diagrams explanatory of the operation of the burst detection synchronization circuit. 9...Input signal, 10...Window comparator, 11...Shift register, 12...Digital comparator, 13...Pattern generator,
14...(+) peak hold circuit, 15...
(-) Peak hold circuit, 16...Synchronization pulse,
17...Clock.

Claims (1)

[Claims] 1. A window comparator that binarizes an input signal including a burst signal, a shift register that converts the time-series signal output from the window comparator into parallel, a pattern generator that generates a parallel digital signal, and a It consists of a digital comparator that compares the parallel pattern with the parallel pattern output from the above pattern generator, and detects the match between the binarized pattern of the burst signal in the input signal and the pattern created by the above pattern generator, and A burst detection synchronization circuit characterized by synchronization.