JPH0456479A - Horizontal synchronization detector - Google Patents

Abstract

PURPOSE:To detect a right horizontal synchronizing signal even when the cycle of the horizontal synchronizing signal is disturbed by providing a rising signal generating means which generates a first rising signal, and a horizontal synchronizing signal generating means which generates the horizontal synchronizing signal after generating a second rising signal generated for the period of repetition just before the first rising signal is shifted. CONSTITUTION:When the cycle of the horizontal synchronization of an inputted television signal is disturbed largely, a selective circuit 6 selects the output of a delay circuit 10, and outputs the horizontal synchronizing signal which is delayed only in a standard cycle from the horizontal synchronizing signal just before it. However, a counting circuit 14 counts how many times the output pulses of a differentiation circuit 4 and of a differentiation circuit 9 are not continuously superimposed. Then, when the counted result is more than 3, an output signal 1 at a 'high' level is outputted from the circuit 14, and a signal from a holding circuit 12 is inhibited by an OR circuit 13, and the output of a delay circuit 5 is forcibly selected by the selective circuit 6. Thus, the horizontal synchronizing signal corrected at a right position can be detected, even when the cycle of the horizontal synchronization of the inputted television signal is disturbed largely.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a horizontal synchronization detection device for detecting a horizontal synchronization signal from a television signal.

[Conventional technology]

A conventional horizontal synchronization detection device will be described with reference to the drawings.

FIG. 5 is a block diagram showing an example of a conventional horizontal synchronization detection bag and arrangement, and FIG. 6 is a time chart of signals of various parts of the conventional example shown in FIG.

The operation of the conventional example shown in FIG. 5 will be explained with reference to FIG.

First, the synchronization separation circuit 15 separates the composite synchronization signal n from the television signal input from the input terminal l, and the differentiation circuit 16 differentiates the falling edge of the composite synchronization signal to output a differential pulse 0. Normally, the differential pulse is inputted as it is to one holding circuit through the OR circuit 17, expanded to a predetermined pulse width of the horizontal synchronization signal, reversed in polarity, and outputted from the output terminal 2 as the horizontal synchronization signal r. Output. The holding circuit 18 holds the differential pulse output from the OR circuit 17 for a period slightly shorter than the standard period of horizontal synchronization of the television signal and outputs it to the OR circuit 17 as an output signal p, so that the horizontal synchronization in the vertical synchronization period is Even if the equivalent pulse between
7, and is not output from output terminal 2 as a horizontal synchronizing signal.

FIG. 7 shows a time chart of signals of various parts when the period of horizontal synchronization of the input television signal is greatly disturbed in the conventional example shown in FIG. In FIG. 7, H indicates the standard period of horizontal synchronization of the television signal.

In FIGS. 5 and 7, the horizontal synchronizing signal B input at a shorter period than H with respect to the immediately preceding horizontal synchronizing signal is inhibited by the OR circuit 17 by the output signal p of the holding circuit 18, so the output terminal No output from 2. If the holding time of the holding circuit 18 is set short, inhibition will not occur, but if the holding time is shortened, if there is noise in the composite synchronization signal, it will be erroneously detected as a horizontal synchronization signal. For example, if there is noise instead of a horizontal synchronizing signal at the position B in FIG. 7, the noise will not be inhibited and will be erroneously detected as a horizontal synchronizing signal.

In addition, detection is performed for horizontal synchronization signal C input with a period longer than H with respect to the previous horizontal synchronization signal, but when the next horizontal synchronization signal comes to the normal position, the horizontal synchronization signal Since the interval with C is shorter than H, it is not detected in the same way as in the case of B.6 [Problem to be solved by the invention] As mentioned above, in the conventional horizontal synchronization detection device, the horizontal synchronization of the input television signal is not detected. The disadvantage is that the horizontal synchronization signal cannot be detected if the period of the signal is greatly disturbed. For example, in the case of a VTR signal, skew distortion occurs near the end of each field of the television signal due to switching of the rotating head, which may disrupt the period of the horizontal synchronizing signal as shown in B and C in Figure 7. In this case, the conventional horizontal synchronization signal detection device cannot correctly detect the horizontal synchronization signal.

[Means to solve the problem]

The horizontal synchronization detection device of the present invention includes a rising signal generating means for detecting the rising edge of a composite synchronizing signal from an input television signal and generating a first rising signal; When the repetition period of the rising signal deviates by more than a predetermined tolerance value of a predetermined standard repetition period, a second rising signal is generated in the repetition period immediately before the deviation of the first rising signal. sync signal generating means for generating a horizontal sync signal; the rising signal generating means includes a sync separation circuit for separating and outputting a composite sync signal from an input television signal; a differentiating circuit, and the synchronizing signal generating means has a second differentiating circuit that differentiates the output signal of the second holding circuit, and each output signal from the first differentiating circuit and the second differentiating circuit. an AND circuit that takes a logical product of differential pulses, a first holding circuit that holds the output of the AND circuit for a predetermined period of time, and a first delay circuit that delays the output signal of the first differentiating circuit. , a second delay circuit that delays the output signal of the second differentiating circuit; and a selection control signal that selects one of the output signals output from the first delay circuit and the second delay circuit. a selection circuit to select, a counting circuit that counts the number of differential pulses output from the selection circuit and is reset by the output signal of the first holding circuit, and an output from the first holding circuit and the counting circuit. an OR circuit that logically sums each output signal and outputs it as the selection control signal of the selection circuit; and an OR circuit that holds the output signal of the selection circuit for about one predetermined horizontal synchronization period of the television signal. It has a second holding circuit and a third holding circuit that holds the differential pulse output from the selection circuit so that it has a predetermined pulse width of a horizontal synchronizing signal of the television.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, the horizontal synchronization detection device of this embodiment includes a synchronization separation circuit 3 that separates and outputs a composite synchronization signal from a television signal input from an input terminal 1, a differentiation circuit 4 that differentiates the composite synchronization signal, A differentiating circuit 9 that differentiates the output signal of the holding circuit 8, an AND circuit 11 that takes the logical product of each differential pulse output from the differentiating circuit 4 and the differentiating circuit 9, and a predetermined constant value for the output of the AND circuit 11. A holding circuit 12 that holds time, a delay circuit 5 that delays the output signal of the differentiating circuit 4, and a delay circuit 10 that delays the output signal of the differentiating circuit 9
A selection circuit 6 selects one of the output signals output from the delay circuit 5 and the delay circuit 10 using a selection control signal, and a holding circuit 12 counts the number of differential pulses output from the selection circuit 6. Counting circuit 1 reset by output signal
4, an OR circuit 13 which logically sums each output signal outputted from the holding circuit 12 and the counting circuit 14 and outputs it as a selection control signal for the selection circuit 6; The holding circuit 8 holds the differential pulse outputted from the selection circuit 6 so that it has the pulse width of the television horizontal synchronization signal. -0 FIG. 2 is a diagram showing the timing relationship of the signals of each part in the present embodiment shown in FIG. 1, FIG. This figure is an enlarged view of a portion of FIG. 3, showing the timing relationship of each signal when the input television signal is switched.

Next, the operation of this embodiment will be explained using FIG. 1, FIG. 2, FIG. 3, and FIG. 4.

The synchronization separation circuit 3 separates a composite synchronization signal from the television signal a input from the input terminal 1, and the differentiation circuit 4 differentiates the falling edge of the composite synchronization signal and outputs a differential pulse C.

Normally, this signal is delayed by a delay circuit 5, selected by a selection circuit 6, and inputted to a holding circuit 8. In the holding circuit 8, this pulse is held for a time slightly shorter than the standard period of horizontal synchronization of the television signal and is output. The retention time will be described later. A differential pulse f is outputted from the differentiating circuit 9 at the falling point of the output signal e of the holding circuit 8.

Normally, the positions of the output pulses of the differentiating circuit 4 and the differentiating circuit 9 substantially coincide in time, and the AND circuit 11 outputs an AND output. Since the signal obtained by holding the high level pulse output from the AN circuit 11 in the holding circuit 12 for a certain period of time is input to the selection circuit 6 as a selection control signal through the OR circuit 13, the selection circuit 6 is delayed. Select the signal for circuit 5.

That is, the selection circuit 6 selects the signal of the delay circuit 5 only when the differential pulses of the differentiating circuits 4 and 9 overlap near the falling edge of the horizontal synchronizing signal of the input television signal, and then selects the signal of the delay circuit 5. A signal for the delay circuit 10 is selected. The output signal j of the delay circuit 5 selected by the selection circuit 6 is widened by the holding circuit 7 to the pulse width of the horizontal synchronizing signal, has its polarity inverted, and is outputted from the output terminal 2 as a horizontal synchronizing signal.

In FIG. 3, H indicates the standard period of horizontal synchronization of television signals, and D indicates the pulse width of the differential pulses in the differentiating circuits 4 and 9. D is determined by the tolerance deviation of the horizontal synchronization period of the input television signal from H, and if it is too short, the output pulses of differentiating circuits 4 and 9 will overlap even if the period of the horizontal synchronizing signal deviates even slightly from H. As will be described later, instead of a horizontal synchronizing signal separated from the input signal, a free-running horizontal synchronizing signal with period H is output. Delay circuit 5 and delay circuit 10
The amount of delay and the holding time of the holding circuit 12 are such that the timing allows selecting one of the differential pulses output from the differentiating circuit 4 and the differentiating circuit 9 using the selection control signal of the selection circuit 6 output from the holding circuit 12. Therefore, the delay amount needs to be D or more, and the holding time needs to be twice or more. In addition, the holding circuit 8
The holding time becomes HD so that when the horizontal synchronization period of the input television signal is disturbed, the period of the replaced horizontal synchronization signal becomes H, as will be described later.

During the vertical synchronization period, only the horizontal synchronization signal is detected as shown in FIG.
Since it does not coincide in time with the differential pulse f output from the selector circuit 6, it is not selected by the selection circuit 6, and is not output from the output terminal 2 as a horizontal synchronizing signal.

Next, the operation when the period of horizontal synchronization of the input television signal is greatly disturbed will be explained with reference to FIGS. 1 and 4.

When the horizontal synchronization period of the input television signal deviates from the standard period H by more than D, the differential pulse C output from the differential circuit 4 and the differential pulse f output from the differential circuit 9 will temporally Note that if there is no overlap, the output of the AND circuit 11 remains at the "°low" level. As a result, the selection circuit 6 selects the output of the delay circuit 10, and a horizontal synchronization signal delayed by H from the previous horizontal synchronization signal is output. However, for example, if the input TV signal is switched and the output pulses of the differentiating circuits 4 and 9 do not always overlap, a horizontal synchronizing signal that is out of phase with the input TV signal will continue to be output, so the counting circuit 14 It is counted how many times the output pulses of the circuit 4 and the differentiating circuit 9 are not in the same pattern.

In other words, when the output pulses of the differentiating circuit 4 and the differentiating circuit 9 overlap, a "high" level pulse is output from the holding circuit 12, so this pulse resets the counting circuit 14.0If the output pulses do not overlap, the counting circuit 14 will not be reset. The differential pulses of the differential circuit 9 output from the selection circuit 6 are counted. When the counting result becomes 3 or more, the counting circuit 14 outputs a "high" level output signal 1, the OR circuit 13 inhibits the signal from the holding circuit 12, and the output signal of the delay circuit 5 is forcibly selected by the selection circuit 6. to select it.

FIG. 4 shows a case where the input television signal is switched at point A.

〔Effect of the invention〕

As explained above, the present invention includes a rising signal generating means for detecting the rising edge of a composite synchronizing signal from an input television signal and generating a first rising signal, and a rising signal generating means for generating a first rising signal from the rising signal generating means. When the repetition signal of the rising signal deviates by more than a predetermined tolerance value in a predetermined standard repetition period, a second rising signal is generated in a repetition period immediately before the deviation of the first rising signal. By having a synchronization signal generating means for generating a horizontal synchronization signal,
Even if the period of horizontal synchronization of the input television signal is greatly disturbed, the horizontal synchronization signal corrected to the correct position can be detected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
4 is a diagram showing the timing relationship of each part of the present embodiment shown in FIG. 1, FIG. 5 is a block diagram showing an example of a conventional horizontal synchronization detection device, and FIGS. FIG. 3 is a diagram showing the timing relationship of each part of the conventional example shown in the figure. 1...Input terminal, 2...Output terminal, 3.15...
Synchronous separation circuit, 4, 9.16... Differential circuit, 5.10
...Delay circuit, 6...Selection circuit, 7, 8.12.1
8゜19...Holding circuit, 11...AND circuit, 13
．． 17...OR circuit, 14...counting circuit. a, m...input television signal, b...synchronization separation circuit 3
Output signal of C... Output signal of differentiation circuit 4, d...
Output signal of delay circuit 5, e...output signal of holding circuit 8, f...output signal of differentiation circuit 9, g...delay circuit 1
0 output signal, h...ANI) output signal of circuit 11,
i... Output signal of holding circuit 12, j... Selection circuit 6
Output signal of k... Output signal of holding circuit 7, l...
Output signal of the counting circuit 14, n... Output signal of the synchronous separation circuit 15, 0... Output signal of the differentiating circuit 16, p...
Output signal of holding circuit 18, q...output signal of OR circuit 17, r...output signal of one holding circuit.

Claims (1)

[Scope of Claims] 1. Rising signal generating means for detecting the rising edge of a composite synchronizing signal from an input television signal and generating a first rising signal; and the first rising edge from the rising signal generating means. When the repetition period of the signal deviates by more than a predetermined tolerance value of a predetermined standard repetition period, a second rising signal that occurs in the repetition period immediately before the deviation of the first rising signal is generated to generate a horizontal signal. 1. A horizontal synchronization detection device comprising: synchronization signal generating means for generating a synchronization signal. 2. The rising signal generating means has a synchronization separation circuit that separates and outputs a composite synchronization signal from the input television signal, and a first differentiation circuit that differentiates the composite synchronization signal, and the synchronization signal generation means a second differentiating circuit that differentiates the output signal of the second holding circuit; an AND circuit that takes the logical product of each differential pulse output from the first differentiating circuit and the second differentiating circuit; a first holding circuit that holds the output of the circuit for a predetermined period of time; a first delay circuit that delays the output signal of the first differentiating circuit; and a second holding circuit that delays the output signal of the first differentiating circuit.
a second delay circuit that delays the output signal of the differentiating circuit;
a selection circuit that selects either one of the output signals output from the first delay circuit and the second delay circuit using a selection control signal; and a selection circuit that selects the number of differential pulses output from the selection circuit. A counting circuit that counts and is reset by the output signal of the first holding circuit, and a logical sum of each output signal output from the first holding circuit and the counting circuit, and the selection control signal of the selection circuit. an OR circuit that outputs a differential pulse output from the selection circuit; a second holding circuit that holds the output signal of the selection circuit for approximately one period of predetermined horizontal synchronization of the television signal; 2. The horizontal synchronization detection device according to claim 1, further comprising a third holding circuit that maintains the pulse width of the horizontal synchronization signal of the television set to a predetermined pulse width.