JPS60229590A - Timing pulse generating circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit and to improve the stability and precision by controlling the start of counting with a vertical synchronizing signal, counting a horizontal synchronizing signal and comparing the counted horizontal synchronizing signal with a horizontal line set externally, and outputting a timing pulse when they coincide with each other. CONSTITUTION:When a composite video signal (a) is inputted from a composite video signal input 2, a synchronous separating circuit 3 separates and outputs its synchronizing signal. Therefore, the synchronizing signal is inputted to a horizontal synchronizing signal generating circuit 4 and a vertical synchronizing signal generating circuit 5 to generate a horizontal synchronizing signal (e) and a vertical synchronizing signal (d). A monostable multivibrator circuit 6 expands the vertical synchronizing signal (d) like a signal (g). A counter 7 starts counting the horizontal synchronizing signal (e) after the signal (g) is outputted and supplies the result to a comparator 8. The comparator 8 compares the count signal with the horizontal line set with a line setting signal from a line setting signal input 1 and outputs the timing pulse signal (h) for the horizontal line when they coincide with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to a timing pulse generation circuit for selecting a particular horizontal line of a television signal.

[Prior art and its problems]

In general, in a television signal, various types of Ia@ may be superimposed on a specific horizontal line within a vertical erasing period. In this case, a synchronization signal that determines the vertical timing and horizontal timing is required to determine the superimposition line, but in order to eliminate the need for external synchronization for ease of external connection, we A method of separating synchronization is often used.

Here, FIGS. 1(4) to 1(g) are time charts showing signal waveforms in the conventional example. As described above, the input composite video signal a (see FIG. 1 (4)) is switched between signals having different average video levels by a switch or the like (not shown). This switching is generally performed at the switching timing M near the vertical synchronization signal d (see (c) in the same figure), so the waveform of the signal a is as shown in Fig. 1 (4). 0
3), the response could not keep up with the signal shown in Figure 1 (C
), there were cases where the separated synchronization signal C was missing. This becomes more noticeable as the difference in average video level increases.

Therefore, the horizontal synchronization signal e (first
However, if you simply calculate the horizontal synchronization, the timing pulse signal f will be as shown in Figure 1 (G), even though the solid line is the normal timing, as shown in Figure 1 (G).
There is a drawback that the timing may be shifted as shown by the signal f' indicated by the middle broken line.

One way to avoid this is to regenerate synchronization by controlling the oscillator using a separate synchronization signal, but this method has the drawbacks of complicating the circuit and causing characteristic problems such as jitter.

Another disadvantage is that the output of a mono multi-circuit that is simply triggered by a vertical synchronization signal is insufficient in terms of stability and accuracy to determine the timing of a horizontal line.

[Purpose of the invention]

The present invention generates a horizontal synchronizing signal and a vertical synchronizing signal No. 14 from a synchronizing signal separated from an input composite video signal, and extends the vertical synchronizing signal to a constant width using a mono multi-circuit. By controlling the counter to count horizontal synchronization signals from the point in time, and using a comparator to create a horizontal line timing that matches the set line,
It is an object of the present invention to provide a timing pulse generation circuit which generates a stable timing pulse of a horizontal line when switching a video signal near a vertical synchronization signal, and which eliminates the above-mentioned drawbacks.

[Structure of the invention]

To achieve this, the configuration of the present invention includes means for separating a synchronization signal from a composite video signal, means for generating a horizontal synchronization signal from the separated synchronization signal, and means for generating a vertical synchronization signal from the separated synchronization signal. monomulti means for outputting a signal using the vertical synchronization signal as a trigger; means for controlling the start of counting by the signal and dividing the horizontal synchronization signal; It is constructed with a comparison means that compares the horizontal line and outputs a timing pulse when -i.

[Embodiments of the invention]

Next, one embodiment will be described with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the timing pulse generation circuit according to the present invention, and its operation is illustrated in FIGS.
, (G), and lυ as appropriate.

In Figure 2, l is a line setting signal input, 2 is a composite video signal input, or 3 is a sync separation circuit, 4 is a horizontal sync signal generation circuit, 5 is a vertical sync signal generation circuit, and 6 is a mono multi circuit. , 7 is a counter, 8 is a comparator, and 9 is a timing pulse signal output.

Next, the operation will be explained. When a composite video signal a (see FIG. 1) is input from the composite video signal input 2, the synchronization separation circuit 3 separates and outputs a synchronization signal from it. Therefore, the horizontal synchronization signal generation circuit 4 and the vertical synchronization signal generation circuit 5 receive the synchronization signal as shown in FIG.
)>, a horizontal synchronizing signal e1 and a vertical synchronizing signal d are generated. The monomulti circuit 6 receives the vertical synchronizing signal d and stretches it as a signal g shown in FIG. 1(G). Therefore, the counter 7 starts counting the horizontal synchronizing signal e after the output of the signal g, and supplies this to the comparator 8. Therefore, the comparator 8 compares the horizontal line set by the line setting signal from the line setting signal 1 with the above count signal, and when they match, the timing pulse signal h of the corresponding horizontal line (I reference) is output.

As mentioned above, in the vicinity TA affected by switching, rough timing is output to the mono multi circuit 6, and the horizontal line is determined by counting the horizontal synchronization signal e, so that stable horizontal Line timing pulse signals can be obtained.

[Effects of the Invention] As described above, the timing pulse generation circuit according to the present invention generates a horizontal synchronization signal and a vertical synchronization signal from a synchronization signal separated from an input composite video signal, and generates a horizontal synchronization signal and a vertical synchronization signal. is extended to a certain width using a mono multi-circuit, the counter is controlled to count horizontal synchronization signals from a stable point after the vertical synchronization signal, and a comparator is used to create the timing of the horizontal line that matches the set line. Therefore, it is possible to generate a horizontal line timing pulse that matches horizontal synchronization when switching images near a vertical synchronization signal, and the circuit configuration is also simple.

[Brief explanation of drawings]

Figures 1 (4) to (2) are time charts of various signals of the conventional timing pulse generation circuit or the present invention, respectively;
The figure is a block diagram of an embodiment of the timing pulse generation circuit according to the present invention. l...Line setting signal input 2...Composite video signal input 3...Synchronization separation circuit 4...Horizontal Synchronization signal generation circuit 5...Vertical synchronization signal generation circuit 6...Monomulti circuit 7...Counter 8...Comparator 9...Timing pulse signal output Applicant: NEC Corporation

Claims (1)

[Claims] means for separating a synchronization signal from a composite video signal; means for generating a horizontal synchronization signal from the separated synchronization signal; and means for generating a vertical synchronization signal from the separated synchronization signal;
mono-multi means for outputting a signal using the vertical synchronization signal as a trigger, and the start of counting is controlled by the signal;
means for counting the horizontal synchronization signal; comparing the counted horizontal synchronization signal with an externally set horizontal line;
1. A timing pulse generation circuit comprising: comparison means that outputs a timing pulse when a match occurs.