JPS62154878A - Synchronizing signal separating circuit - Google Patents

Abstract

PURPOSE:To remove the influence of external noise and to obtain a highly accurate horizontally synchronizing signal by providing two monostable multivibrators for separating a horizontally synchronizing signal from a composite synchronizing signal and an AND circuit. CONSTITUTION:The outputs of the 1st and 2nd monostable multivibrators 2, 3 are supplied to the AND circuit 4 and a pulse with the same width as that of a horizontally synchronizing signal is generated from an output terminal 5. When external noise is included in a composite synchronizing signal, the 1st vibrator 2 generates a pulse by the noise, but the 2nd vibrator 3 generates an output with almost the same period as a horizontally synchronizing pulse, the outputs of the vibrators 2, 3 are supplied to the AND circuit 4 and the AND operation of both the inputs is executed to cancel the noise, so that the noise generated in the horizontally synchronizing pulse period is not outputted.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is based on NTSC (National Te1
The present invention relates to a synchronization signal separation circuit that separates only a horizontal synchronization signal from a composite synchronization signal of a television based on the system.

[Conventional technology]

FIG. 3 is a circuit diagram showing a conventional synchronization signal separation circuit that performs frequency separation of a composite synchronization signal, that is, separates a horizontal synchronization signal with a high frequency component and a vertical synchronization signal with a relatively low frequency component. be. In the figure, 1 is an input terminal into which a composite synchronization signal is input, 6 is a differentiating circuit that obtains a horizontal synchronization signal by differentiating the input composite synchronization signal, and 7 is an integration circuit that obtains a vertical synchronization signal from the composite synchronization signal. , 8 and 9 are the differentiating circuits 6., 9, and 9, respectively. The output terminal of the integrating circuit 7, 10 is an AFC (Automatic Freq
11 is a comparator.

In the conventional synchronization signal separation circuit having the above configuration, input terminals 1. Output terminal 5a.

The waveforms of 5b are as shown in FIG. A horizontal synchronizing signal as shown in FIG. 4 (bl) appears at the output terminal 5b, and a vertical synchronizing signal as shown in FIG. 4 (C1) appears at the output terminal 5b. The differentiating circuit that separates the horizontal synchronization signal from the composite synchronization signal has a property of easily passing high-frequency alternating current, so if pulse noise is superimposed on the composite synchronization signal, it will easily pass through. Differential circuit 6
This causes serious interference with horizontal scanning.

Therefore, in the conventional synchronization signal separation circuit shown in Fig. 3, in order to escape from this interference, a noise prevention circuit called a noise killer circuit is added to the synchronization separation circuit (amplitude separation circuit) that extracts the synchronization signal from the video signal. It removed pulse noise.

Furthermore, the conventional synchronization signal separation circuit is affected by the cutting pulse and equalization pulse for stably maintaining the horizontal synchronization of the receiver. That is, the period of time TI shown in FIG. ), the frequency is twice that in other sections.When this signal is sent to the AFC circuit 10, if the AFC circuit 10 is poorly adjusted, the output frequency will fluctuate, causing the television screen to change. This causes the upper part of the AF to bend, etc.
The damping factor of the C circuit is set large to slow down the response of the system, and the lock range of the AFC circuit 10 is set to several hundred H.
It is configured to take an extremely narrow range of about z. This means that when designing the AFC circuit 10, considerable accuracy is required for component constants and the like.

[Problem that the invention seeks to solve]

Since the conventional synchronization signal separation circuit is configured as described above, it is necessary to provide a noise prevention circuit to remove pulse noise, and the circuit becomes complicated in order to make the AFC circuit highly accurate. There were problems such as:

This invention was made to solve these problems, and has improved noise resistance, and can separate the horizontal synchronization signal from the composite synchronization signal with a small number of parts without the need for a special additional circuit. The purpose is to obtain a synchronization signal separation circuit.

[Means for solving problems]

The synchronizing signal separation circuit according to the present invention includes a first monostable multivibrator that is triggered by the leading edge of a pulse of an input composite synchronizing signal and outputs a pulse, and a first monostable multivibrator that is triggered by the trailing edge of the first monostable multivibrator. and a second monostable multivibrator that outputs pulses, and an AND circuit that performs an AND of output pulses output from the first and second monostable multivibrators.

[Effect]

In this invention, 1. The second monostable multivibrator outputs constant pulses based on the pulses of the composite synchronization signal, and these output pulses are ANDed in an OR circuit to produce the output of the first monostable multivibrator. Based on this, a pulse with the same width as the horizontal synchronization signal is obtained, and a noise pulse is removed based on the output of the second monostable multivibrator.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, 1 is an input terminal into which a composite synchronization signal is input, and 2 is a leading edge of the input composite synchronization signal (in this embodiment, the falling edge of the signal). ) to output a pulse with the same width as the horizontal synchronization.
3 is a second iE'L which outputs a pulse of a predetermined width by the trailing edge (falling edge of the signal in this embodiment) of the first monostable multivibrator 2.
A stable multivibrator, 4 is an AND circuit, and 5 is an output terminal from which a horizontal synchronizing signal is output.

The operation of the synchronization signal separation circuit of the present invention configured as described above will now be described. Here, FIG. 4 is a time chart showing waveforms at each part in FIG.
l is a pulse waveform indicating a decoupled synchronization signal input to input terminal 1, (b) is a pulse waveform output from the first monostable multivibrator 2, and (C) is a pulse waveform output from the second monostable multivibrator. (d) shows the output waveform of the AND circuit 4, respectively.

First, when a composite synchronizing signal, which is an NTSC signal, is supplied to the input terminal 1, this signal is supplied to the first monostable multivibrator 2, and the rising edge (leading edge) of the pulse shown in FIG. ), a pulse with the same width (approximately 4.76 μS) as the horizontal synchronizing pulse is generated from the output Q (Fig. 2 (b)).The output of the first monostable multivibrator 2 is then A pulse is supplied to the monostable multivibrator 3, and a pulse of one horizontal period (63.5 μs) is output from the monostable multivibrator 2 based on the trailing edge of the pulse shown in FIG. width, i.e. the width minus the width of the horizontal sync pulse (58
, 7 μs) is generated from the output Q (FIG. 2(C)).

Furthermore, the output of the first monostable multivibrator 2 shown in FIG. 2 (bl) and the output of the second monostable multivibrator 3 shown in FIG. Then, a pulse having the same width as the horizontal synchronization shown in FIG. 2 Fdl is generated from the output terminal 5.

Here, if the above-mentioned composite synchronization signal contains external noise, the first monostable multivibrator 2 generates a pulse due to the noise, but the second monostable multivibrator 3 generates a horizontal synchronization pulse. The outputs of almost the same period are generated, and the outputs of the monostable multivibrators 2 and 3 are supplied to the AND circuit 4, and the noise is canceled by taking the AND, so the noise generated between the horizontal synchronizing pulse periods is No output.

〔Effect of the invention〕

As described above, according to the present invention, two monostable multivibrators and an AND circuit are provided to separate the horizontal synchronization signal from the composite synchronization signal, and the structure is digitally processed, thereby eliminating the influence of external noise. At the same time, it is possible to obtain a highly accurate horizontal synchronization signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a synchronization signal separation circuit according to an embodiment of the present invention, FIG. 2 is a time chart showing the operation of its main parts, and FIG. 3 is a block diagram showing a conventional synchronization signal separation circuit.
FIG. 4 is a time chart showing the operation of the main parts. In the figure, 2.3 is a monostable multivibrator, and 4 is an AND circuit. Note that the same reference numerals in each figure indicate the same or equivalent parts. Agent Masu Oiwa! ij I<2 idiots) Fig. 1 1 Input terminal) 2 A to Imahito Maru I now have high 1 - Ku 3, R 5 Maru to Bay Converter 4 衾 G cho V type times T) 5 To the furnace Figure 2 (d) L Figure 3 Figure 4 (C) Procedural correction sound (spontaneous June 118, 1988)

Claims (1)

[Claims] (1) A composite synchronization signal containing a horizontal synchronization signal and a vertical synchronization signal in a television is input, and the composite synchronization signal is input to a synchronization signal separation circuit that separates only the horizontal synchronization signal from the composite synchronization signal. , a first monostable multivibrator that is triggered by a leading edge of each pulse of the composite synchronization signal and outputs an output pulse with a pulse width that matches a predetermined horizontal synchronization signal; and an output pulse of the first monostable multivibrator. and is triggered by the trailing edge of each output pulse, and outputs an output pulse having a pulse width equal to the width of one cycle of the predetermined horizontal synchronization signal minus the output pulse width. A synchronous signal separation circuit comprising: a vibrator; and an AND circuit which receives output pulses from the first and second monostable multivibrators and calculates an AND.