JPH03283890A - Color separation circuit - Google Patents

Abstract

PURPOSE:To stably and accurately detect the phase shift of a color demodulation axis by correcting the reduction of the amplitude of an input analog color television signal by an AGC circuit. CONSTITUTION:The size of quantization errors e1 and e2 are inversely proportional to color burst amplitude A1 and A2, and assuming the color burst amplitude A1 as the amplitude of a color burst signal in a color television signal with the maximum amplitude, the color burst amplitude is reduced from A1 to A2 and the quantization error is increased from e1 to e2 when an input signal is decreased. Therefore, a function to correct the amplitude when the amplitude of the color burst of the input signal is decreased by the AGC circuit 4 is attached. Thereby, it is possible to detect the phase shift of the demodulation axis with high accuracy from the color burst.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color separation circuit, and more particularly to a color separation circuit that digitally separates color signals from a color television signal.

[Conventional technology]

Color separation circuits that digitally separate color signals from color television signals are well known.

FIG. 2 is a block diagram of a conventional color separation circuit. Input terminal 1
The analog power signal a is sent to the A-D converter 7.
The digital color television signal g is output to the color separator 8. The color separator 8 inputs a digital color television signal g and a phase shift signal r to be described later, separates color signals, sends a color difference signal i to an average value calculation circuit 13 and an output terminal 15, and outputs a color difference signal j to an average value. They are output to the calculation circuit 14 and output terminal 16, respectively. Average value calculation circuit 13゜The average value calculation circuit 14 inputs the values of the two color difference signals i and j obtained by color separation in the color burst interval to the input terminal 18.
The sample is sampled a certain number of times using the input sampling clock O, and the average value of the obtained sample values is output. As a result, the phase shift of the color burst is calculated by the phase shift calculation circuit 11 based on the average value p and average value q found for the two color difference signals i and j, respectively, and the phase shift signal r is outputted to the color separator 8. do.

[Problem to be solved by the invention]

In the NTSC color television signal, for example, R-
When performing color separation on the Y and B-Y axes, R-Y is 0 in the color burst section if color separation is performed correctly.
, B-Y take negative values.

However, when reproducing the demodulation axis of the color signal from a digitized color television signal, if the amplitude of the reference color burst is small, the quantization error becomes large and the phase shift calculation circuit contains a large quantization error. Therefore, there is a drawback that the phase shift of the demodulation axis of the color signal includes an error, and the RY signal is not 0 when demodulating the color burst section.

[Means to solve the problem]

The color separation circuit of the present invention includes a first video switch that inputs an analog color television signal and switches between outputting a color burst section and other sections of the analog color television signal; a color burst amplitude detection circuit that inputs an output and outputs a color burst amplitude; an AGC circuit that inputs an output of the color burst section and always outputs a constant amplitude regardless of fluctuations in the amplitude of the color burst signal; a second video switch that switches between an output other than the color burst section and an output of the AGC circuit; a first A-D converter that digitizes the output of the second video switch; and a first A-D converter that digitizes the output of the second video switch; a second A-D converter that digitizes the output of the detection circuit; and the first A-D converter.
a color separator that separates the output of the converter into two color signals, a C1 signal and a 02 signal, and outputs the two color signals; and a first level converter that converts the level of the C1 signal according to the output value of the second A-D converter. a second converter for converting the level of the C2 signal according to the output value of the second A-D converter;
a level converter, and a third video switch that switches between the output of the first level converter and the C1 signal;
a fourth video switch that switches between the output of the second level converter and the C2 signal; a first average value calculation circuit that calculates the average value of the values of the C1 signal in the color burst section; and the C21 signal. A second average value calculation circuit that calculates the average value of the values in the color burst section of the signal, and a phase shift between the color burst and the color demodulation axis based on the output values of the first and second average value calculation circuits. and a phase shift calculation circuit that calculates and outputs it to the color separator.

〔Example〕

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

FIG. 1 is a block diagram of an embodiment of the color separation circuit of the present invention.

The color separation circuit of the embodiment shown in FIG. 1 includes a video switch 2 as a first video switch that inputs an analog color television signal and switches output between a color burst section and other sections; a color burst amplitude detection circuit 3 which inputs the output of the interval and outputs the color burst amplitude; and an AGC which inputs the output of the color burst interval and always outputs a constant amplitude regardless of fluctuations in the amplitude of the color burst signal. a circuit 4, a video switch 5 as a second video switch that switches between the output of the area other than the color burst and the output of the AGC circuit 4;
a first A- for digitizing the output of the video switch 5;
An A-D converter 6 as a D converter, an A-D converter 7 as a second A-D converter for digitizing the output of the color burst amplitude detection circuit 3, and an A-D converter 7 as a second A-D converter that digitizes the output of the color burst amplitude detection circuit 3.
A color separator 8 that separates the output of the converter 6 into two color signals, a C1 signal and a C2 signal, and outputs the two color signals, and a first level converter that converts the level of the 01 signal according to the output value of the A-D converter 7. a level converter 9 that converts the level of the 02 signal according to the output value of the A-D converter 7, a level converter 10 as a second level converter that converts the level of the 02 signal according to the output value of the A-D converter 7, and a level converter 10 that switches between the output of the level converter 9 and the C1 signal. 3 video switch 11 and level converter 1 as video switch
A video switch 12 as a fourth video switch that switches the output C2 signal of 0, and an average value calculation circuit 13 as a first average value calculation circuit that calculates the average value of the values in the color burst section of the C1 signal. and an average value calculation circuit 14 and an average value calculation circuit 1 as a second average value calculation circuit that calculates the average value of the values in the color burst section of the C2 signal.
A phase shift calculation circuit 17 calculates a phase shift between the color burst and the color demodulation axis based on the output value of 3.degree. 14 and outputs it to the color separator 8.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

In this embodiment, the color demodulation axis is R-Y for explanation.

This will be explained as BY.

Input analog color TV signal a from input terminal 1,
The video switch 2 switches between the color burst signal and the other partial signals C, and outputs the color burst signal to the color burst amplitude detection circuit 3 and the AGC circuit 4.

The color burst amplitude detection circuit 3 detects the amplitude of the color burst signal d and converts the color burst amplitude value d into A-
The AGC circuit 4 outputs a color burst signal e with a constant amplitude regardless of the amplitude of the color burst signal e, and the video switch 5 outputs a color burst signal e that is not separated by the video switch 2. Signal C and color burst signal e are combined, analog color television signal f is input to AD converter 6 and digitized, and digital color television signal g is output to color separator 8. The A-D converter 7 digitizes the color burst amplitude value d and outputs the color burst amplitude value to the level converter 10. The color separator 8 separates the color signal from the digital color television signal g, outputs the color difference signal (R-Y) to the level converter 9 and the average value calculation circuit 13, and outputs the color difference signal (B-Y) j. It is output to the level converter 10 and the average value calculation circuit 14.The level converter 9 outputs the input color difference signal (RY) i as a level conversion value k according to the color burst amplitude value, and outputs the level conversion value k according to the color burst amplitude value. 11, the color difference signal (RY) i is switched to the level conversion value k only in the color burst section, and the color difference signal (RY) m is outputted to the output terminal 15.The level converter 10 converts the input color difference signal (B- Y) Output the level conversion value 1 according to the output signal from j, and switch it to video switch 1.
2, only the color burst section of the color difference signal (B-Y) j is switched to the level conversion value l, and the color difference signal (B-Y)
r+ is output to the output terminal 16.

Therefore, the control voltage of the AGC circuit 4 or the color difference signal not added to the color burst signal can be extracted from the output terminal 1'5.16. In the average value calculation circuit 13, the input terminal 1
Input the sampling clock 0 from the
-Y) Sample the value in the interval of color burst t~ of i a certain number of times, calculate the average of the sample values for each line, and send the average value (RY)p to the color burst phase shift calculation circuit 17. Output. Similarly, the average value calculation circuit 14 inputs the sampling clock 0 from the input terminal 18, samples the value in the color burst section of the color difference signal (B-Y) j a certain number of times, and calculates the average of the sample values for one line. and outputs the average value (B-Y)q to the color burst phase shift calculation circuit 17. The phase shift calculation circuit 17 inputs the average value (R-Y) p and the average value (B-Y) q, and calculates R
- The phase shift of the color burst is calculated from the fact that the two color difference signals of the Y signal and the B-Y signal in the color burst interval are 0 for R-Y and negative for B-Y, and the phase shift signal r is Output to separator 8.

FIG. 3 shows the relationship between color burst amplitude and quantization error. The magnitude of the quantization error e 1 +e2 is inversely proportional to the color burst amplitudes A I and A 2 . Therefore, if the color burst amplitude Al is the amplitude of the color burst signal in the maximum amplitude color television signal, if the level of the input signal decreases for some reason, the color burst amplitude will also decrease from A1 to A2, and as a result, the quantum The conversion error will increase from el to e2. As a result, in the conventional circuit, the color burst phase shift calculation circuit 17 cannot calculate the phase shift of the demodulation axis from the normal color burst with high accuracy when the level of the input signal is low. Therefore, in the present invention, by providing the AGC circuit 4 with a function to correct the decrease in the amplitude of the color burst of the input signal, it is possible to accurately calculate the phase shift of the demodulation axis from the color burst. And so. In this embodiment, the color demodulation axes are R-Y and B-Y, but it is clear that the effects of the present invention can be applied to any demodulation axis, even if the demodulation value of the color burst is different. It is.

〔Effect of the invention〕

As explained above, the present invention corrects the amplitude reduction of an input analog color television signal using an AGC circuit, thereby converting two color difference signals obtained by color separation from a color burst of a color television signal, for example, R-Y, B. This has the effect that it is possible to stably and accurately detect the phase shift of the color demodulation axis based on the average values found for -Y, without being affected by fluctuations in the level of the input signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the color separation circuit of the present invention, FIG. 2 is a block diagram of a conventional color separation circuit, and FIG. 3 is an explanatory diagram showing the relationship between quantization errors in the amplitude of color bursts. It is. 1...Input terminal, 2...Video switch, 3...
Color burst amplitude detection circuit, 4...AGC circuit, 5
...Video switch, 6...A-D converter, 7
...A-D converter, 8...color separator, 9...
Level converter, 10... Level converter, 11... Video switch, 12... Video switch, 13...
Average value calculation circuit, 14... Average value calculation circuit, 15...
- Output terminal, 16... Output terminal, 17... Phase shift calculation circuit, 18... Input terminal, a... Analog color television signal, b... Color burst signal, C...
Partial signal, d... Color burst amplitude value, e... Color burst signal, f... Analog color television signal, g... Digital color television signal, h... Color burst amplitude value, i...・Color difference signal, j...Color difference signal, k...Level exchange value, l...Level conversion value, m
...Color difference signal, n...Color difference signal, 0...Sampling clock, p...Average value, q...Average value, r.
...Phase shift signal.

Claims (1)

[Claims] a first video switch that inputs an analog color television signal and switches output between a color burst section and other sections of the analog color television signal; and a first video switch that inputs an output of the color burst section and outputs a color burst amplitude; A color burst amplitude detection circuit that outputs a color burst amplitude, and A that inputs the output of the color burst section and always outputs a constant amplitude regardless of fluctuations in the amplitude of the color burst signal.
a GC circuit, a second video switch that switches between an output other than the color burst section and an output of the AGC circuit, and a first A-D converter that digitizes the output of the second video switch; A second A-D converter that digitizes the output of the color burst amplitude detection circuit, and a C_D converter that digitizes the output of the first A-D converter.
a color separator that separates and outputs two color signals, a C_1 signal and a C_2 signal; a first level converter that converts the level of the C_1 signal according to an output value of the second A-D converter; a second level converter that converts the level of the C_2 signal according to an output value of a second A-D converter; and a third video switch that switches between the output of the first level converter and the C_1 signal. a fourth video switch that switches between the output of the second level converter and the C_2 signal; and a first average value calculation circuit that calculates an average value of the values of the C_1 signal in a color burst section. a second average value calculation circuit that calculates the average value of the values in the color burst section of the C_2 signal; and a color burst and color demodulation axis based on the output values of the first and second average value calculation circuits. and a phase shift calculating circuit that calculates a phase shift between the color separator and the color separator.