JPH08317415A - Crosstalk reduction circuit - Google Patents

Abstract

PURPOSE: To prevent a crosstalk due to a synchronous noise from being prominent by synchronizing the synchronizing signal of a self-exciting synchronizing signal generation circuit with a video signal being processed. CONSTITUTION: NTSC processing is performed by switching switches S1, S2 and S4 to ((1) sides, demodulating a Y/C video signal to an RGB signal by a color demodulation/synchronizing separating part 1, separating the synchronizing signal, and outputting it from the switch S2. When RGB signal processing is performed, the switches S1, S2 are switched to (2) sides, and the RGB signal and the synchronizing signal are outputted via the switches S1, S2, and simultaneously, the synchronizing signal is separated to horizontal and vertical synchronizing signals, and the horizontal synchronizing signal is applied to the terminal (1) of the switch S3 and a 1/2-frequency divider 3, and the switch S3 is switched to (1) side when a horizontal frequency shows nearly 15kHz, and to (2) side when it shows 31kHz, and a signal of nearly 15kHz is synthesized with the vertical synchronizing signal from an H/V separating part by an H/V synthesis part 4, and the switch S4 is switched to (2) side when the horizontal frequency shows nearly 31kHz, and the signal is applied to the color demodulation/ synchronizing separator part, then, the synchronizing signal is synchronized with the signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video crosstalk reduction circuit, and a self-excited sync signal generation circuit for synchronizing a sync signal generated by a self-excited sync signal generation circuit with a sync signal of a video signal being processed. To reduce crosstalk caused by the synchronization signal.

[0002]

[Prior Art] Horizontal frequency is approximately 15KHz, 24KHz or
An input section of two or more systems for the video signal separated into three primary colors of R (red), G (green) and B (blue) such as 31KHz and the NTSC signal (video signal) is provided. The input NTSC signal is separated into a luminance signal and a color signal (or separated into a luminance signal and a color signal and input),
An apparatus for converting color signals into R-Y and BY color difference signals, demodulating the color difference signals and the luminance signal into RGB three primary color signals, and switching and outputting the RGB signals input in the three primary colors is provided. is there. In such an apparatus, when the NTSC signal is switched to the NTSC signal side in the absence of the input of the NTSC signal, the synchronous circuit becomes an asynchronous state and the screen is disturbed. For this reason, a self-excited sync signal generation circuit (which synchronizes with an NTSC signal when it is input) is provided at the input part of the NTSC signal, and the color demodulation circuit and the sync circuit are generated by the sync signal generated by this circuit. It is synchronized so that the screen is not disturbed due to asynchronization. However, since this synchronizing signal generation circuit is a self-exciting type that generates a synchronizing signal by itself, the frequencies are very close to the RGB synchronizing signals, but the phases do not match, or there is a slight difference in frequency. R
When the horizontal frequency of the GB signal is approximately 15KHz, which is the same as the horizontal frequency of the NTSC signal, or approximately 31KHz, which is double the horizontal frequency of the NTSC signal, noise resulting from the operation of the synchronization circuit, etc. is mixed into the RGB signal system and appears as crosstalk on the screen. There's a problem.

[0003]

SUMMARY OF THE INVENTION In view of the above, the present invention takes the above-mentioned point into consideration. When processing an RGB signal, the horizontal frequency of the RGB signal is substantially the same as the horizontal frequency of the NTSC signal, approximately 15 KHz or 2 kHz.
If the frequency is doubled to approximately 31 KHz, the input of the NTSC signal to the self-excited sync signal generation circuit is cut, and the RGB sync signal (when the horizontal frequency is approximately 15 KHz) or the horizontal sync signal is separated and halved. Frequency divided by (when approximately 31KHz)
Then, the self-excited synchronizing signal generating circuit is synchronized again with the signal synthesized with the vertical synchronizing signal so that the synchronous noise generated in the processing circuit of the NTSC signal enters within the blanking period of the RGB signal and crosses the screen. It is to prevent talk interference from appearing.

[0004]

In order to solve the above-mentioned problems, the present invention has at least two systems of video signal input sections, and switches the video signals from these video signal input sections to perform the required processing. In the output video signal processing device,
A self-excited sync signal generation circuit for synchronizing a video signal input from the first video signal input unit with a sync signal input to the signal processing unit from the second video signal input unit. Provided is a crosstalk reduction circuit adapted to synchronize with a synchronization signal of a first video signal.

[0005]

Since the crosstalk reducing circuit according to the present invention is configured as described above, the self-excited synchronous signal generating circuit provided in the NTSC signal processing circuit is provided in the processing of the RGB signal having the horizontal frequency of about 15 KHz or about 31 KHz. The sync signal of the RGB signal or the horizontal sync signal is separated and divided in half (in the case of approximately 31 KHz), and synchronized with the signal that is combined with the vertical sync signal. Prevent crosstalk interference from appearing on the screen when noise enters the RGB signal processing circuit.

[0006]

Embodiments of the crosstalk reducing circuit according to the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of essential parts of an embodiment of a crosstalk reducing circuit according to the present invention. In the figure, reference numeral 1 denotes a color demodulation / synchronization separation unit that outputs a luminance (Y) signal and a color (C) signal to RY and BY.
Demodulated into the color difference signal of R, G and B
Color demodulation circuit that converts to color signals, and self-excited sync signal generation circuit that synchronizes with this sync signal when a sync signal is input (horizontal frequency of approximately 15 KHz when no sync signal is input)
When the Y / C signal of NTSC (switch S4: side) is input, the color demodulation circuit demodulates it into three color signals of R, G and B, and switches S1
, And at the same time, separates the synchronization signal and outputs it to the terminal of switch S2, and when the signal from H / V combiner 4 (switch S4: side) is input, H / V combiner The synchronizing signal synchronized with the signal from No. 4 is output to the terminal of the switch S2 (in this case, there is no RGB signal output). A H / V separation unit 2 separates the RGB sync signal into a horizontal (H) sync signal and a vertical (V) sync signal. 3 is 1/2
The frequency divider divides the horizontal synchronizing signal of approximately 31 KHz from the H / V separation unit 2 into a frequency of 1/2. An H / V synthesizer 4 synthesizes the horizontal sync signal from the switch S3 or the signal from the 1/2 frequency divider and the vertical sync signal from the H / V separator 2 into a composite sync signal.

FIG. 2 is a block diagram of an essential part of another embodiment of the crosstalk reducing circuit according to the present invention. Reference numeral 11 denotes a mode discriminating portion which discriminates the mode of the RGB signal on the basis of the synchronizing signal of the RGB signal and switches. Switch S3 or switch S4. The other parts are the same as those in FIG.

Next, the operation of the crosstalk reducing circuit according to the present invention will be described with reference to the case of FIG. Interlocking switch S1
As shown in FIG. 3, S2 and S2 are switched to the side when the NTSC signal is processed, and to the side when the RGB signal is processed. Then, in the case of processing the NTSC signal, the switch S4 is turned to the side. The Y signal and C signal separated from the composite video signal by a comb filter or the like, or the signal previously separated into the Y signal and the C signal is input to the terminal of the switch S4, and both the Y signal and the C signal are input to the switch S4. Input to the color demodulation / synchronization separation unit 1 via.
The color demodulation / synchronization separation unit 1 converts the Y / C signal into RY and B signals.
After demodulating to a -Y color difference signal, the Y signal is converted into an RGB signal, which is output to the terminal of the switch S1 and the synchronization signal separated from the Y signal is output to the terminal of the switch S2. Then, the RGB signal from the switch S1 and the synchronization signal from the switch S2 are input to the subsequent processing circuits, respectively, subjected to required processing, and displayed on the display screen.

Further, in the case of processing RGB signals, the interlocking switches S1 and S2 are switched to the respective sides, and the switch S4 is switched to the side. As a result, the RGB signal from the RGB signal input section is input from the terminal of the switch S1 to the subsequent processing circuit via the switch S1, and the synchronous signal input simultaneously with the RGB signal is input from the terminal of the switch S2 via the switch S2. Input to each subsequent processing circuit, and after the required processing, displayed on the display screen. At this time, the switch S4 is switched to the side when the horizontal frequency of the RGB signal is approximately 15 KHz or approximately 31 KHz, and to the side when the horizontal frequency of the RGB signal is approximately 24 KHz, as shown in FIG.
If the horizontal frequency of the B signal is approximately 15KHz, it is approximately 31KH to the side.
For z, switch to the side. The sync signal that is input together with the RGB signal is also input to the H / V separation unit 2,
The / V separation unit 2 separates the horizontal sync signal and the vertical sync signal, and the horizontal sync signal is applied to the terminal of the switch S3 and 1/2.
It is input to the frequency divider 3, frequency-divided to 1/2, and output to the terminal of the switch S3. The horizontal synchronizing signal switched by the switch S3 is input to the H / V synthesizing unit 4 together with the vertical synchronizing signal from the H / V separating unit 2 and is generated as a composite synchronizing signal. This composite sync signal is output as it is when the horizontal frequency of the RGB signal is approximately 15 KHz, as shown in FIG.
In the case of approximately 31 KHz, the frequency is divided into two and is output as approximately 15 KHz, so that the composite sync signal is approximately the same.

As a result, in the RGB signal processing mode,
If the horizontal frequency is about 15 KHz or about 31 KHz, the color demodulation / sync separation unit 1 has a horizontal frequency of about 15 KHz as described above.
The horizontal frequency of the sync signal generated by the built-in self-excited sync signal generation circuit is synchronized with this approximately 15 KHz, and therefore the synchronous noise generated in the color demodulation / sync separation unit 1 etc. Even if the signal is mixed in the RGB signal processing circuit, noise is synchronized with the RGB signal and is located within the blanking period, so that crosstalk interference does not appear on the screen. The horizontal frequency of the RGB signal is approximately 24KH.
In the case of z, the frequency of synchronous noise is far from the frequency of the screen, so it is not visible to the human eye.

In the case of FIG.
RGB signal mode based on the signal synchronization signal (above-mentioned
15 KHz, about 24 KHz, and about 31 KHz), and the switch S3 or the switch S4 is switched in the same manner as above based on the signal from the mode judging section 11.

[0012]

As described above, according to the crosstalk reducing circuit of the present invention, the self-excited type built in the color demodulation / synchronization separation unit when processing the RGB signal having the horizontal frequency of about 15 KHz or about 31 KHz. Since the horizontal sync signal of the sync signal generation circuit is synchronized with the horizontal sync signal of the RGB signal or the horizontal sync signal divided by 2 (in the case of approximately 31 KHz), the synchronous noise generated in this circuit is processed by the RGB signal. Even if it is mixed in the circuit, the crosstalk interference does not appear on the screen.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts of an embodiment of a crosstalk reduction circuit according to the present invention.

FIG. 2 is a block diagram of a main part of another embodiment of the crosstalk reducing circuit according to the present invention.

FIG. 3 is a diagram illustrating a mode of each switch corresponding to a mode of an input signal.

FIG. 4 is an example of a synchronization signal applied to a synchronization signal generation circuit.

[Explanation of symbols]

 1 color demodulation / synchronization separation unit 2 H / V (horizontal / vertical synchronization signal) separation unit 3 1/2 divider 4 H / V (horizontal / vertical synchronization signal) synthesis unit 11 Mode discrimination unit S1, S2 interlocking switch S3 , S4 switch

Claims (7)

[Claims] 1. A video signal processing apparatus having at least two systems of video signal input sections, switching video signals from these video signal input sections, performing required processing, and outputting.
A self-excited sync signal generation circuit for synchronizing a video signal input from the first video signal input unit with a sync signal input to the signal processing unit from the second video signal input unit. A crosstalk reduction circuit adapted to synchronize with a synchronization signal of a first video signal. 2. The second video signal input section is used for inputting an NTSC video signal, and the frequency of the horizontal synchronizing signal of the video signal input to the first video signal input section is approximately 15 KHz.
In the case, the crosstalk reducing circuit according to claim 1, wherein the sync signal generated by the sync signal generating circuit is synchronized with the sync signal from the first video signal input section. 3. A frequency divider for dividing the frequency of the horizontal synchronizing signal from the first video signal input section into ½ by using the second video signal input section for inputting an NTSC video signal. Is provided, and when the frequency of the horizontal synchronizing signal of the video signal input to the first video signal input unit is approximately 31 KHz, the frequency divider divides the frequency of the horizontal synchronizing signal by a factor of two to perform the synchronization. 2. The crosstalk reducing circuit according to claim 1, wherein the synchronizing signal generated by the signal generating circuit is synchronized with the signal from the frequency divider. 4. A first switch for switching a horizontal synchronizing signal input via the first video signal input section and a signal from the frequency divider, and an input via the first video signal input section. And a mode discriminating unit for discriminating the mode of the signal to be generated, and the frequency of the horizontal synchronizing signal is approximately 31 KH.
When z is determined, the first switch is switched to the frequency divider side, the signal from the first switch is applied to the synchronization signal generation circuit, and the signal synchronized with the signal from the first switch is generated. The crosstalk reduction circuit according to claim 3, 5. An H / V separation unit that separates a composite sync signal input via the first video signal input unit into a horizontal sync signal and a vertical sync signal, and a composite sync of the horizontal sync signal and the vertical sync signal. An H / V synthesizing unit for synthesizing the signal, a horizontal synchronizing signal from the H / V separating unit is applied to the frequency divider, and a horizontal synchronizing signal from the H / V separating unit is applied by the first switch. Switching with the signal from the frequency divider,
Input the signal from the switch to the H / V combiner, and
5. The crosstalk reducing circuit according to claim 4, wherein the composite sync signal synthesized by the V synthesizer is applied to the sync signal generating circuit. 6. A second switch for switching between the signal from the second video signal input section and the signal from the first switch or the H / V synthesizing section is provided, and the mode discriminating section has a horizontal frequency of about 15 KHz or When it is determined that the frequency is approximately 31 KHz, the second switch is set to the first switch or the H / V.
6. The crosstalk reduction circuit according to claim 4, wherein the signal is output from the second switch to the synchronizing signal generation circuit so that the switching is switched to the synthesizing unit side. 7. The first video signal input section is set so as to input signals separated into three primary colors of red, green and blue, and the second video signal input section is provided with a luminance signal and a color signal. Is set to input the separated signal, a color demodulation circuit is provided in the synchronizing signal generation circuit, and when the video signal separated into the luminance signal and the color signal is input, red, green and blue The crosstalk reduction circuit according to claim 1, claim 2, claim 3, claim 4, claim 5, or claim 6, which is configured to demodulate and output signals of three primary colors.