JPH03224385A - Yc separator circuit - Google Patents

Abstract

PURPOSE:To improve frequency characteristic and S/N characteristic by outputting a 1st signal obtained from an NTSC composite video signal with frequency separation and a 2nd signal passing through a comb-line circuit as a C signal in response to the correlation between the 1st signals apart by 2H to each other. CONSTITUTION:An output signal of a band pass filter 1 is inverted by an inverter 4 and fed to an adder 11. A correlator 8 receives an output signal of the band pass filter 1 and a 2H preceding signal delayed by 2H at 1H delay circuits 3, 6 and takes the correlation of both signals. The correlation degree is fed to a linear gate 10 as a control signal to control the gate 10 in response to the degree of the correlation. When an output of the correlator 8 represents no correlation, a moving contact is moved to the upper end and the output of the band pass filter 1 is extracted as the C signal. As a result, no color blurring is caused in a vertical color component and cross color is improved because general comb-line configuration is ensured at the correlation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a YC separation circuit, and particularly to a dynamic YC separation circuit with improved S/N characteristics and frequency characteristics.

(Prior Art) Conventionally, a line correlation type YC separation circuit using a comb filter is used as a YC separation circuit for separating a luminance signal (Y signal) and a color signal (C signal) from a video signal.

The simplest configuration of the line correlation type YC separation circuit is a two-line comb type YC separation circuit that uses one 1H delay circuit that delays a signal by 1H (one horizontal synchronization signal period).

However, although the comb-shaped operation of this YC separation circuit is effective when there is a correlation between the signal from 1H before and the current signal, if it is operated when there is no correlation between the image signals, the vertical resolution of the chroma signal will be reduced. Deterioration and dot interference occur.

1 has been proposed to solve this problem.
This is a 3-line dynamic square YC separation circuit (J stone type YC separation circuit) as shown in FIG. 2, using two H delay circuits.

In FIG. 2, an NTSC composite video signal (input signal) is supplied to a band pass filter (BPF) 23 that passes a 3.58 MHz chroma band component and a 1H delay circuit 21. The output of the 1H delay circuit 21 is supplied to a bandpass filter 24 having similar characteristics to the bandpass filter 23, a 1H delay circuit 22, and a delay line 26.

The output of the 1H delay circuit 22 is also passed through the bandpass filter 2.
9. In the correlator 27, the current signal, 1H previous signal, and 2H signal supplied from the bandpass filters 23, 24, and 25 are
It receives the previous signal, determines the degree of correlation between these three signals, and outputs the output as a C signal only when it is determined that there is a correlation. The output of the correlator 27 is, for example, one of the three signals mentioned above.

In this way, the correlator 27 generates a Y signal by addition processing in the adder 28 only when there is a correlation, and when there is no correlation, the output of the 1H delay circuit 21 is output as a Y signal.

In the figure, a delay line 26 is a delay line for adjusting the time between the output signal of the 1H delay circuit 21 and the output signal of the correlator 27.

(Problems to be Solved by the Invention) In the conventional YC separation circuit as described above, the following problem occurs because the entire NTSC composite input signal is delayed by the 1H delay circuits 21 and 22.

That is, CCDs are currently widely used as high-precision delay means in high frequency bands, but there are limits to setting the clock frequency for CCD delay operations, and the highest frequency currently in practical use is ( 3.58 x 4 MHz). The actual frequency used at this time is (3,58X2MH
z), and if aliasing noise is considered, the limit is about 500 lines in terms of resolution.

On the other hand, current monitor devices have a resolution of 800 to 900 lines, for example, YC installed in an AV amplifier.
As a separation circuit, the above-mentioned limitations pose a problem. In other words, the conventional YC separation circuit has a problem in terms of frequency characteristics.

Furthermore, in the conventional YC separation circuit described above, noise generated by the CCD constituting the 1H delay circuit is superimposed on the signal.
There is also the problem that the /N characteristics deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a YC separation circuit with improved frequency characteristics and S/N characteristics.

In order to solve the above-mentioned problems, the YC separation circuit according to the present invention frequency-separates the chroma signal from the composite signal and
a bandpass filter that outputs a signal as a signal; a first correlation means that calculates the degree of correlation between signals that are shifted by two horizontal period signal intervals (2H) with respect to the output of the bandpass filter; the first signal; The first correlator receives a second signal obtained by a two-line comb circuit from the first signal, and when it determines that there is a correlation, it outputs the second chroma signal, and when it determines that there is no correlation, it outputs the second chroma signal. Outputting the first chroma signal, or, if the degree of correlation is intermediate, a signal obtained by linearly adjusting the first signal and the second signal according to the degree of correlation, respectively, as a C signal. C signal output means, the composite signal is delayed by the delay time of the band pass filter, and the Y signal output obtained by the difference with the output signal of the band pass filter is shifted by 1H with respect to the first signal. a second correlator that determines the correlation between the signals; and a second correlator that determines the correlation between the first signal and the signal that is 1H apart from the Y signal output when the second correlator determines that there is a correlation. and Y signal output means for outputting the added signal as a Y signal when it is determined that there is no correlation, and outputting the Y signal output as a Y signal.

(Function) The YC separation circuit according to the present invention separates the first signal obtained by frequency-separating the NTSC composite video signal and the second signal that has passed through the comb-shaped circuit by 2H. The signals are distributed in a predetermined manner according to the degree of correlation between the first signals and are output as C signals. Further, the amount of addition of the 3.58 MHz band of the Y signal is changed depending on the degree of correlation between the first signals shifted by 1H. As a result, when uncorrelated, the first
Since the chroma signal is used as the C signal, no vertical color bleeding occurs, and when correlation occurs, a general comb-shaped configuration is used, so cross color is improved. Furthermore, the horizontal resolution of the Y signal during correlation does not deteriorate, and dot interference in the non-correlation area is also improved.

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

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

The NTSC composite video signal (input signal) is 3.
The signal is input to a bandpass filter 1 that passes a chroma band signal of 58 MHz, and a delay line 2 that delays the input signal by the processing time (passage time) in this bandpass filter 1.

The output signal of band pass filter 1 is inverted by inverter 4 and then supplied to adder 11 .

Adder 11 adds the output from inverter 4 and the output from delay line 2 and sends the result to adder 12 . The output of the bandpass filter 1 is also supplied to the 1H delay circuit 3.

For in-phase detection, the correlator 5 correlates the signal from the band-pass filter 1 (current signal) with the 1H previous signal delayed by 1H by the 1H delay circuit 3, and when it is determined that they are in-phase based on the degree of correlation. Only the output of the adder 11 and the output from the correlator 5 (for example, the bandpass filter 1
or the output of the 1H delay circuit 3)
The Y signal is obtained by adding the

Thus, in this embodiment, before adding the 1H delayed signal, the phase comparison (
Since the Y signal based on the output of the correlator 5 is output only when both signals are in phase, dot interference is improved.

The adder 13 adds the output of the bandpass filter 1 (current signal) and the output of the inverter 7<a signal obtained by inverting the previous signal by 1H), and obtains twice the chroma signal during correlation. The output of the adder 13 is halved by a 6 dB attenuator 9 and supplied to a linear gate 10.

The correlator 8 outputs the output signal (current signal) of the bandpass filter 1 and the 2H signal delayed by 2H by the 1H delay circuits 3 and 6.
It receives the signal before H and correlates both signals. For example, if we take the difference between the 2H delayed signal and the undelayed current signal, the output will be zero if both signals are in phase, and the output will be maximum if they are in inverted phase. This degree of correlation is sent to the linear gate 10 as a control signal, and the linear gate 10 is controlled according to the degree of correlation.

The linear gate 10 is configured using, for example, a variable resistor, and one end of the resistor is connected to the output of the bandpass filter 1 (a signal that does not pass through a comb-shaped circuit), and the other end is connected to the output of the attenuator 9. , the movable contact position for extracting the C signal is controlled by the correlation output (degree of correlation) from the correlator 9.

More specifically, for example, if the output value of the correlator 8 indicates that there is no correlation, the movable contact moves to the upper end, takes out the output of the bandpass filter 1 as the C signal, and outputs the color vertically. On the other hand, if the correlation value indicates that there is a sufficient correlation, the movable contact moves to the lower end and takes out the output of the attenuator 9 (comb-shaped circuit passing signal) as the C signal and crosses it. Improved colors.

In other words, with this configuration, the signal passed through the comb-shaped circuit and the signal passed only through the band-pass filter are output in a variable manner according to the degree of correlation. Deterioration is improved.

In the above configuration, since the delay line 2 is for compensating for the time delay caused by the bandpass filter 1, an LC delay circuit can be used, and the LC delay circuit is composed only of passive elements. Not only is there no noise such as that generated in a CCD, etc., but also the frequency characteristics of the Y signal basically depend on the characteristics of this delay line, so it is possible to improve the frequency characteristics.

Further, since the signals delayed by the 1H delay circuits 3 and 6 are the signals (3.58 MHz) passed through the bandpass filter 1, the influence of noise caused by the CCD operation is reduced.

(Effects of the Invention) As explained above, the YC separation circuit according to the present invention frequency-separates the first chroma signal from the NTSC composite video signal, and separates the first chroma signal from the first chroma signal. The second chroma signal that has passed through the comb-shaped circuit is output as a C signal in a predetermined distribution according to the correlation value between the signals that are shifted by 2H time with respect to the first chroma signal.

Therefore, during non-correlation, the first chroma signal is output as a C signal, which eliminates vertical color bleeding, and during correlation, the shell has a comb-shaped configuration, which improves cross color. Become.

On the other hand, in the 3.58 MHz band, the Y signal is added as a correlation output only when there is a correlation with the signal 1H before, so the horizontal resolution of the Y signal during correlation does not decrease, and dot interference during non-correlation does not occur. will also be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a YC separation circuit according to the present invention, and FIG. 2 is a block diagram of a conventional YC separation circuit. 1.23.25...Band pass filter (BPF) 2
．． 26... Delay line (DL>, 3.6, 21.22... 1H delay circuit, 4.7... Inverter, 5, 8.27 Correlator, 9 Attenuator, 1
0...Linear gate, 11.12.13.28...Adder.

Claims (1)

[Claims] The chroma signal is frequency-separated from the composite signal and the first
a bandpass filter that outputs a signal as a signal; a first correlation means for determining the degree of correlation between signals shifted by two horizontal synchronization signal intervals (2H) with respect to the output of the bandpass filter; A second signal obtained by a two-line comb circuit is received from the first signal, and when the first correlator determines that there is a correlation, it transmits the second chroma signal, and when it determines that there is no correlation, it transmits the second chroma signal. 1 chroma signal, or, when the degree of correlation is intermediate, a signal obtained by linearly adjusting the first signal and the second signal according to the degree of correlation, respectively, as a C signal. signal output means; delaying the composite signal by the delay time of the band-pass filter; a Y signal output obtained by a difference between the output signal of the band-pass filter; and a signal shifted by 1H with respect to the first signal; a second correlator that determines the correlation between the two signals; and a sum signal of a predetermined signal among the first signal and the 1H shifted signal and the Y signal output when the second correlator determines that there is a correlation; and Y signal output means for outputting the Y signal output as a Y signal when it is determined that there is no correlation.