JPH05219522A - Yc separator circuit - Google Patents

Abstract

PURPOSE:To attain accurate YC separation even when a nonstandard signal is inputted. CONSTITUTION:A Y signal and a C signal separated by a 1st YC separator circuit 1 employing a low pass filter and a high pass filter to separate the Y signal and the C signal and a 2nd YC separator circuit 2 employing a comb- line filter for separating a luminance signal and a chrominance signal are selected by 1st and 2nd switching circuits selected interlockingly and outputted to 1st and 2nd output terminals. The 1st and 2nd switching circuits 3, 4 are controlled by a switching signal generating circuit to select the output of the 1st YC separator circuit 3 when the relation between the frequency of a synchronous signal in the Y signal and the frequency of a color subcarrier in the C signal is deviated from the substantial relation, that is, when a nonstandard signal is inputted. Thus, even when the nonstandard signal is inputted, accurate YC separation is implemented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a YC separation circuit for a composite color video signal, and more particularly to a YC separation circuit capable of performing accurate YC separation even when a non-standard signal is input.

[0002]

2. Description of the Related Art In a television receiver or VTR, it is necessary to separate a luminance signal (hereinafter referred to as Y signal) and a carrier color signal (hereinafter referred to as C signal) from a composite color video signal. As the separating method, there are a method of extracting a Y signal with a low pass filter and a C signal with a high pass filter, and a method of extracting a Y signal and a C signal with a comb filter.

However, in the former method, since the high frequency component of the Y signal is attenuated by the low pass filter, the horizontal resolution of the reproduced image is lowered. Moreover, since the Y signal component in the same band as the C signal remains in the high-pass filter, cross color is generated on the reproduction screen. on the other hand,
In the latter method, the Y signal is extracted by adding the color video signal at the present time and the composite color video signal delayed by one horizontal scanning period (hereinafter referred to as 1H), so that the vertical resolution can be obtained in the portion where the vertical correlation of the image is small. Will decrease.

Therefore, a technique for switching between the two types of YC separation methods according to the magnitude of the vertical correlation of the image is, for example,
It is disclosed in JP-A-55-150687 and the like.
This YC separation circuit includes a low-pass filter, a first YC separation circuit that separates the Y signal and the C signal by the low-pass filter, a second YC separation circuit that separates the Y signal and the C signal by a comb filter, A switching circuit for selecting the output of the second YC separation circuit and a circuit for detecting the vertical correlation of the input composite color video signal are provided. When the vertical correlation is large, the switching circuit outputs the output of the first YC separation circuit. When the vertical correlation is small, the switching circuit selects the output of the second YC separation circuit.

[0005]

However, in the conventional YC separation circuit disclosed in the above publication, the second YC separation circuit utilizes the fact that the phase of the color subcarrier is inverted every 1H. Since the signal and the C signal are separated, a signal (hereinafter referred to as a non-standard signal) in which the frequency relationship between the burst signal of the color subcarrier such as a VTR reproduction signal and the horizontal synchronization signal is deviated from the original relationship is input terminal. When input, there was a problem that YC separation was not performed accurately.

It is an object of the present invention to solve the above-mentioned problems and to provide a YC separation circuit capable of performing accurate YC separation even when a non-standard signal is input.

[0007]

In order to solve the above problems, the present invention provides a YC separation circuit for separating a Y signal and a C signal of a composite color video signal by using a low pass filter and a high pass filter. First to separate signals
YC separation circuit, a second YC separation circuit that separates the Y signal and the C signal by a comb filter, and first and second YC separation circuits.
A switching circuit that selects the output of the separation circuit, a frequency comparison circuit that detects the frequency relationship between the sync signal in the Y signal and the color subcarrier in the C signal selected by the switching circuit, and switching based on the output of the frequency comparison circuit. A switching control circuit for controlling the circuit is provided, and the output of the first YC separation circuit is selected when the frequency comparison circuit detects that the frequency relationship deviates from the original relationship.

The present invention also provides a composite color video signal of Y
In the YC separation circuit that separates the degree signal and the C signal, an A / D conversion circuit that converts an analog composite color video signal into a digital composite color video signal, and a Y signal from the output of the A / D conversion circuit by a low pass filter and a high pass filter And a first YC separation circuit for separating the C signal, a second YC separation circuit for separating the Y signal and the C signal from the output of the A / D conversion circuit by a comb filter, and first and second YC separation circuits. It is controlled by a switching circuit that selects the output of the circuit, a color demodulation circuit that demodulates the C signal selected by the switching circuit, a hold circuit that holds the level of the burst signal of the output signal of the color demodulation circuit, and an output of the hold circuit. Switching control circuit that controls the switching circuit based on the output of the voltage control oscillation circuit for generating the demodulation reference signal and the hold circuit. If, Y switching circuit selects
A circuit for multiplying a synchronizing signal in the signal to generate a clock signal to be supplied to each of the circuits, and selects the output of the first YC separation circuit when the output of the hold circuit is equal to or greater than or equal to a predetermined value. As configured.

[0009]

According to the present invention, since the YC separation circuit is constructed as described above, the first and second YC separation circuits separate the Y signal and the C signal from the composite color video signal, and the switching circuit forms the first circuit. Alternatively, the output of the second YC separation circuit is selected. The switching circuit detects the frequency relationship between the frequency of the sync signal in the Y signal and the frequency of the color subcarrier in the C signal selected by the switching circuit with the frequency comparison circuit, and when the frequency relationship deviates from the original relationship, that is, It is controlled to select the output of the first YC separation circuit when a non-standard signal is input. Therefore, accurate YC separation can be performed even if a nonstandard signal is input.

Further, according to the present invention, the A / D conversion circuit converts the analog composite color video signal into a digital composite color video signal, and the first and second YC separation circuits output from the output of the A / D conversion circuit. The Y signal and the C signal are separated, and the switching circuit selects the output of the first or second YC separation circuit. Further, a clock signal obtained by multiplying the synchronizing signal in the Y signal selected by the switching circuit is supplied to all circuits including the A / D conversion circuit that process digital signals. The switching circuit demodulates the C signal selected by the switching circuit by the color demodulation circuit, holds the level of the burst period of the demodulated output by the hold circuit, and when the output level of the hold circuit is above or below a predetermined value, It is controlled to select the output of the YC separation circuit of 1.

The output of the hold circuit is supplied to the demodulation reference signal oscillator circuit, and the clock signal is supplied to each circuit. Therefore, the output of the hold circuit is the frequency of the synchronizing signal in the Y signal selected by the switching circuit. And corresponds to the deviation of the frequency of the color subcarrier in the C signal from the original frequency relationship. Therefore, when the switching circuit is controlled as in the present invention, when the frequency of the synchronizing signal in the Y signal and the frequency of the color subcarrier in the C signal deviate from the original frequency relationship, that is, a non-standard signal is input. Since the output of the first YC separation circuit is selected during the operation, accurate YC separation can be performed even if a non-standard signal is input.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing the configuration of a YC separation circuit according to the first embodiment of the present invention, and FIG. 2 is a timing chart for explaining its operation. Here, the waveforms a to h in FIG. 1 are (a) to (h) in FIG. The configuration and operation of this embodiment will be described below with reference to FIGS. 1 and 2.

The composite color video signal received by the antenna ANT and output from the tuner or the composite color video signal input from the video input terminal is a switching circuit SW.
Are supplied to the first YC separation circuit 1 composed of a low-pass filter and a high-pass filter and the second YC separation circuit 2 composed of a comb filter. Then, the Y signal and the C signal which are the outputs of the first and second YC separation circuits are selected by the first and second switching circuits 3 and 4 which are switched in conjunction with each other, and the first output terminal 5 is selected.
To the second output terminal 6 and the C signal to the second output terminal 6.

The Y signal a output from the first switching circuit 3 is separated from the horizontal synchronizing signal b by the sync separating circuit 7, and the frequency is multiplied by N (for example, 910) by the N multiplying circuit.
And is input to the first input terminal of the frequency comparison circuit 11. The burst signal of the C signal d output from the second switching circuit 4 is separated by the burst gate circuit, multiplied by the subcarrier regeneration circuit 10 (for example, 4 times), and converted into a continuous wave. It is input to the second input terminal of the frequency comparison circuit 11.

The frequency comparison circuit 11 outputs a DC voltage ferr according to the frequency difference between the input signals at the first and second input terminals. Then, the DC voltage ferr is the reference voltage V
It is compared with ref, and when it becomes Vref or more, the comparator 12 outputs a high-level voltage g. The output of the comparator 12 is supplied to the switching timing determination circuit 13, where the logical operation is performed with the output of the sync separation circuit 7 to generate the switching timing signal h generated during the horizontal blanking period to generate the first and the first timing signals. Two
To the switching circuits 3 and 4.

The above frequency comparison circuit 11, comparator 12 and switching timing determination circuit 13 constitute a switching signal generation circuit. The operation will be described in detail below. When the composite color video signal is an NTSC standard signal, the horizontal sync signal frequency f _H and the color subcarrier frequency fsc have a frequency relationship of 910 f _H = 4 fsc (1). However, in the case of a non-standard signal, it deviates from the frequency relationship shown in equation (1).

When the frequency of the horizontal synchronizing signal b output from the sync separation circuit 7 is f1 and the frequency of the color subcarrier output from the subcarrier reproducing circuit 10 is f2, the first frequency comparing circuit 11 outputs Input terminal of frequency 9
A signal of 10f1 and a signal of frequency f2 are supplied to the second input terminal. Therefore, the output signal of the frequency comparison circuit 11 becomes a DC voltage corresponding to ferr = 910f1-f2 (2).

Here, as shown in FIG. 2, the operation of switching the input composite color video signal from the standard signal to the non-standard signal and again to the standard signal will be considered. First, if the standard signal is input, ferr
Since = 0, the output g of the comparator 12 is at low level, and the switching timing signal h is also at low level.
As a result, the output of the second YC separation circuit 2 is selected by the first and second switching circuits 3 and 4.

Next, when a non-standard signal is input,
r ≠ 0. When this ferr becomes Vref or more,
Since the output g of the comparator 12 becomes high level, the switching timing signal h changes to high level during the horizontal retrace line period.
As a result, the first and second switching circuits 3 and 4 are switched so as to select the output of the first YC separation circuit 1 during the horizontal blanking period. Here, the reason why the first and second switching circuits 3 and 4 are switched to the horizontal retrace line period is to prevent the switching from affecting the image.

When the standard signal is input again, ferr
= 0, the output g of the comparator 12 becomes low level, and the switching timing signal h changes to low level during the horizontal blanking period. As a result, the first and second switching circuits 3 and 4 are switched so as to select the output of the second YC separation circuit 2 again in the horizontal blanking period. The vertical separation signal may be separated by the synchronization separation circuit 7. In that case, it is necessary to set the multiplication number of the N multiplication circuit 8 to 455 × 525. In addition, the frequency of the signal input to the frequency comparison circuit 11 is set to 2 instead of 4 times the color subcarrier.
It may be doubled.

(Second Embodiment) FIG. 3 is a block diagram showing the configuration of a YC separation circuit according to the second embodiment of the present invention, and FIG. 4 is a timing chart for explaining its operation. Here, the waveforms of i to n in FIG. 3 are from (i) to FIG.
(N). Note that, in FIG. 4, the waveform of a digital signal is illustrated in an analog manner for convenience of description.

The input composite color video signal is YC separated, and based on the frequency relationship between the horizontal sync signal or vertical sync signal in the Y signal and the color subcarrier signal in the C signal,
The basic idea of switching is the same as in the first embodiment.
The difference between this embodiment and the first embodiment is that (1) the first embodiment may be analog processing or digital processing, whereas this embodiment is digital processing. (2) In this embodiment, the C signal is demodulated and the burst level thereof is held to obtain a signal corresponding to ferr.

In FIG. 3, the input analog composite color video signal is converted into a digital composite color video signal by the A / D conversion circuit 21, and the first YC separation circuit 22 and the comb which are composed of a low-pass filter and a high-pass filter. Type YC separation circuit 23 composed of a mold filter
Is supplied to. Then, the digital Y signal and the digital C signal, which are the outputs of the first and second YC separation circuits, are switched in interlock with each other.
4, 25, and D / is applied to the first output terminal 27.
The Y signal converted into the analog signal by the A conversion circuit 26 and the C signal converted into the analog signal by the D / A conversion circuit 28 are output to the second output terminal 29, respectively.

The sync signal is separated by the sync separation circuit 32 from the digital Y signal output from the first switching circuit 24 (the same as in FIG. 2A if described in analog) (see FIG. 2B). The same), the clock generation circuit 33
Causes the frequency to be multiplied by M. The output l of the clock generation circuit 33 is supplied as a clock signal to each circuit that processes a digital signal. In this embodiment, the A / D conversion circuit 2
Since the sampling frequency in 1 is set to 4 times the frequency fsc of the color subcarrier, M = 9 when the digital sync separation circuit 32 separates the horizontal sync signal.
Set to 10.

The digital C signal i output from the second switching circuit 25 is demodulated by the demodulation circuit 30 and output to the third output terminal, and the burst gate circuit 34 extracts the level of the burst period. It Then, the level of the extracted burst period is held by the hold circuit 35, and the low pass filter 36
And is supplied to a VCO (voltage controlled oscillator circuit) 37 that generates a demodulation reference signal. This burst gate circuit 3
4, hold circuit 35, low-pass filter 36, VCO
37 forms a loop, and controls so that the level of the burst period of the RY demodulated signal becomes 0, for example. By this control, even if the output 1 of the clock generation circuit 33 has an incorrect phase or frequency with respect to the burst signal, it is possible to obtain a correctly demodulated color demodulation output.

The output k of the digital low pass filter 36 is supplied to the comparison circuit 38. Then, when it becomes equal to or higher than the reference voltage Vref, the output m of the comparison circuit 38 becomes high level. The output m of the comparison circuit 38 is supplied to the switching timing determination circuit 39, where the output of the sync separation circuit 32 is logically operated to create the switching timing signal n generated during the horizontal blanking period to generate the first and the first signals. It outputs to the second switching circuits 24 and 25.

The comparison circuit 38 and the switching timing determination circuit 39 described above constitute a switching signal generation circuit. Less than,
The operation will be described in detail. Since the present embodiment performs digital processing, if the frequency of the clock signal fluctuates, it affects the operation of each circuit. Demodulation circuit 3 now
Considering the demodulation output of the RY signal of 0, the phases of the RY signal and the burst signal are orthogonal to each other. Therefore, when the input composite color video signal is the NTSC standard signal, the level of the burst period of the demodulation signal is However, when the input composite color video signal is a non-standard signal, the frequency of the output of the clock generation circuit 33 deviates from 4 fsc, so that the level of the demodulated signal in the burst period does not become 0. Since the frequency of the color subcarrier is relatively stable even in the non-standard signal, the level of the burst period becomes a level corresponding to the difference between the frequency of the color subcarrier and the frequency of the synchronizing signal. That is, the burst period of the signal i obtained by demodulating the RY signal by the burst gate circuit 34 is extracted, and the output j passed through the hold circuit 35 and the low-pass filter 36 is the difference between the frequency of the sync signal and the frequency of the color subcarrier. It will be a corresponding level.

Here, as shown in FIG. 4, consider the operation when the input composite color video signal is switched from the standard signal to the non-standard signal and again to the standard signal. First, when the standard signal is input, the frequency of the clock signal l = 910f _H = 4fsc, so the level of the demodulated signal j during the burst period is 0, and the output k of the low-pass filter 36 is also 0. Therefore, the output m of the comparison circuit 38 is low level, and the output n of the switching timing determination circuit 39 is also low level. As a result, the output of the second YC separation circuit 23 is selected by the first and second switching circuits 24 and 25.

Next, when a non-standard signal is input, the frequency of the clock signal k becomes ≠ 910f _H = 4fsc.
The level of the demodulated signal j in the burst period is not 0, and the output k of the low pass filter 36 is not 0 either. And
When the level of the output k of the low-pass filter 36 becomes Vref or more, the output m of the comparison circuit 38 becomes high level, so that the output n of the switching timing determination circuit 39 changes to high level during the horizontal blanking period. As a result, during the horizontal blanking period, the first and second switching circuits 24 and 25 are operated by the first YC.
It switches to select the output of the separation circuit 22.

When the standard signal is input again, the level of the demodulated signal j in the burst period becomes 0, and the output k of the low-pass filter 36 also becomes 0. Therefore, the output m of the comparison circuit 38
Becomes low level. Therefore, the output n of the switching timing determination circuit 39 changes to the low level during the horizontal blanking period. As a result, the first and second switching circuits 24 and 25 are switched so as to select the output of the second YC separation circuit 23 again during the horizontal blanking period.

Also in this embodiment, the vertical sync signal may be separated by the sync separation circuit 32. It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention. For example, each of the above embodiments is NTS
Although it is applied to the C signal, it goes without saying that the present invention can be applied to the PAL signal.

Further, in the first embodiment, the switching may be performed when the value of ferr is less than a predetermined negative value,
In the second embodiment, the switching may be performed when the output k of the low pass filter 36 is a negative predetermined value or less.

[0033]

As described above in detail, according to the present invention, the frequency of the synchronizing signal in the Y signal and the frequency of the color subcarrier in the C signal are deviated from the original frequency relationship. YC with low-pass filter and high-pass filter
Since the separation circuit and the YC separation circuit using the comb filter are selected, the following effects can be obtained. (1) Accurate YC separation is possible regardless of whether the composite color video signal is a standard signal or a non-standard signal. (2) If the composite color video signal is a standard signal, a high resolution Y signal can be obtained. (3) By configuring the YC separation circuit with a digital circuit, a clock signal based on a color burst or a clock generated from a synchronization signal can be used as a clock signal for driving a delay circuit used to realize a comb filter. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a YC separation circuit according to a first embodiment of the present invention.

FIG. 2 is a timing chart explaining the operation of the YC separation circuit according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a YC separation circuit according to a second embodiment of the present invention.

FIG. 4 is a timing chart for explaining the operation of the YC separation circuit according to the second embodiment of the present invention.

[Explanation of symbols]

 1, 22 First YC separation circuit 2,23 Second YC separation circuit 3,24 First switching circuit 4,25 Second switching circuit 7,32 Sync separation circuit 11 Frequency comparison circuit 21 A / D Conversion circuit 30 Demodulation circuit 33 Clock generation circuit 34 Burst gate circuit 35 Hold circuit 36 Low-pass filter 37 VCO 38 Comparison circuit

Claims (2)

[Claims] 1. A YC separation circuit for separating a luminance signal and a carrier color signal of a composite color video signal, comprising: (a) a first YC separation circuit for separating the luminance signal and the carrier color signal by a low pass filter and a high pass filter. (B) a second YC separation circuit that separates the luminance signal and the carrier color signal by a comb filter; (c) a switching circuit that selects the output of the first and second YC separation circuits; ) A frequency comparison circuit for detecting the frequency relationship between the sync signal in the luminance signal selected by the switching circuit and the color subcarrier in the carrier color signal; and (e) controlling the switching circuit based on the output of the frequency comparison circuit. And a switching control circuit for controlling the frequency, the first YC separation circuit when the frequency comparison circuit detects that the frequency relationship deviates from the original relationship. YC separation circuit characterized by selecting the output of. 2. A YC separation circuit for separating a luminance signal and a carrier color signal of a composite color video signal, comprising: (a) an A / D conversion circuit for converting an analog composite color video signal into a digital composite color video signal; A first YC separation circuit that separates the luminance signal and the carrier color signal from the output of the A / D conversion circuit by a low-pass filter and a high-pass filter; and (c) the luminance signal by the comb filter from the output of the A / D conversion circuit. A second YC separation circuit that separates the carrier color signal, (d) a switching circuit that selects the output of the first and second YC separation circuits, and (e) a carrier color signal that is selected by the switching circuit. A color demodulation circuit for demodulation, (f) a hold circuit for holding the level of the burst signal of the output signal of the color demodulation circuit, and (g) control by the output of the hold circuit. A demodulation reference signal generating voltage controlled oscillation circuit, (h) a switching control circuit for controlling the switching circuit based on the output of the hold circuit, and (i) a synchronization signal in the luminance signal selected by the switching circuit. And a circuit for generating a clock signal to be supplied to each of the circuits, wherein the output of the first YC separation circuit is selected when the output of the hold circuit is equal to or greater than or equal to a predetermined value. YC separation circuit.