JPH0335874B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color demodulation circuit for a video reproducing device;
In particular, the present invention relates to a color demodulation circuit for a video playback device that plays back video using a color video signal based on the PAL (Phase Alternation Line) system.

PAL corresponding to the nth (n is a natural number) scanning line
The color video signal E _M n of the system is given by the following equation.

E _M n=Y+Eusinωct +(-1) ⁿ Evcosωct...(1) ωc≒2πf _H (m-1/4)...(2) Here, Y is the luminance signal, Eu and Ev are the color difference signals B-Y , RY are shown, respectively. Note that B and R indicate blue and red signals, respectively. Further, f _H is a horizontal scanning frequency, and m is a natural number. The coefficient (-1) _o in equation (1) means phase inversion for each horizontal scanning line, and the Ev
The components are transmitted by balanced modulation of subcarrier signals of (-1) _o cos ωct having a phase difference of 180° from each other for each horizontal scanning line. Therefore, the color burst signal is required to have information for inverting the phase of the subcarrier of the Ev component line by line on the image receiving side. Therefore, the color burst signal is ±
The phase is switched to 135° for each line, and the phase-inverted version is sent out.

FIG. 1 shows a conventional color demodulation circuit in a device that reproduces video using such a PAL color video signal. In FIG. 1, a PAL color video signal is supplied to a bandpass filter 1. As shown in FIG. The bandpass filter 1 is configured such that its passband is approximately equal to the frequency band of a carrier color signal included in a PAL color video signal. The carrier color signal component is extracted by this band filter 1 and supplied to a 1H (one horizontal scanning period) delay circuit 2, addition circuit 3, and subtraction circuit 4. The signal delay time in 1H delay circuit 2 is (π/2) × 1H
The time is set to be longer or shorter by (1/ωc). Therefore, in order to prevent the occurrence of vertical stripe interference, the phase of the subcarrier is shifted by π/2 between two consecutive scanning lines in the same field, so that the phase of the carrier color signal is exactly the same as the phase 1H earlier. However, the phase of the carrier color signal outputted from the 1H delay circuit 2 about 1H earlier almost matches the phase of the input signal. The output of the 1H delay circuit 2 is supplied to an addition circuit 3 and a subtraction circuit 4. In the adder circuit 3, when the output of the 1H delay circuit 2 is added to the carrier color signal, the Ev component of the carrier color signal is canceled and only the Eu component is outputted from the adder circuit 3. Further, in the subtraction circuit 4, for example, the output component of the 1H delay circuit 2 is subtracted from the carrier color signal, so that the Eu component of the carrier color signal is canceled and only the Ev component is outputted from the subtraction circuit 4. The outputs of these adder circuits 3 and subtracter circuits 4 are outputted to a B-Y demodulator 5, respectively.
and is supplied to the RY demodulator 6. Both the BY demodulator 5 and the RY demodulator 6 are composed of, for example, a synchronous detection circuit and a low-pass filter. B-
The synchronous detection circuit in each of the Y demodulator 5 and the R-Y demodulator 6 includes a 90° phase shifter 7 and a PAL switch 8.
Detection subcarrier signals output from each are supplied. The 90° phase shifter 7 outputs a signal obtained by shifting the phase of the color subcarrier signal by 90°. In addition, PAL switch 8 outputs the color subcarrier signal and this color subcarrier signal.
The output of the 180° phase shifter 9 which outputs a signal obtained by shifting the phase by 180° is alternately outputted every 1H. The BY demodulator 5 and the RY demodulator 6 receive the detection subcarrier signal from the 90° phase shifter 7 and the PAL switch 8, respectively, and receive the BY signal and the RY signal. is demodulated and output.

However, the band filter 1 in the above configuration
Since components other than carrier color signal components near the frequency of the carrier color signal are mixed into the output of the carrier color signal, many high frequency components near the frequency of the carrier color signal, such as luminance signals generated in response to characters or kimono patterns, are mixed into the output. When the included luminance signal is present in a color video signal, so-called cross color occurs, which is a phenomenon in which a colored short horizontal line appears at the edge of a vertical line in the resulting image, giving the appearance of blurring.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color demodulation circuit that can demodulate color difference signals while reliably removing luminance signals and preventing problems such as cross color.

In the color demodulation circuit according to the present invention, one of two carrier color signals each carrying two color difference signals and a color burst signal are phase-inverted every horizontal scanning period.
For a PAL color video signal, a color demodulation circuit in a video reproducing device demodulates the carrier color signal by a subcarrier obtained based on the color burst signal, the color demodulation circuit demodulating the carrier color signal using a subcarrier obtained based on the color burst signal a signal delaying means for delaying a predetermined time; a signal synthesizing means for synthesizing a signal according to the difference between the input and output of the signal delaying means;
The present invention has two demodulation means each demodulating one color difference signal using the subcarrier without phase adjustment.

Hereinafter, the present invention will be explained in detail with reference to FIG.

In FIG. 2, a 1H delay circuit 2, an adder circuit 3,
Subtraction circuit 4, B-Y demodulator 5 and R-Y demodulator 6
are connected in the same way as in FIG. However, in this example, the PAL color video signal is 1H
The signal is supplied to a delay circuit 10 and a subtraction circuit 11.
The 1H delay circuit 10 is composed of, for example, a delay line whose signal delay time is equal to the time corresponding to 1H. The output of this 1H delay circuit 10 is the subtraction circuit 1
1. In the subtraction circuit 11, for example,
By subtracting the output of the 1H delay circuit 10 from the PAL color video signal, a signal corresponding to the difference between the PAL color video signal and this PAL color video signal 1H before is synthesized, and the 1H delay circuit 2,
The signal is supplied to an addition circuit 3 and a subtraction circuit 4. on the other hand,
A single subcarrier signal output from a subcarrier generator (not shown) is supplied to the BY demodulator 5 and the RY demodulator 6. Then, the output of the B-Y demodulator 5 becomes the B-Y signal, and the output of the R-Y demodulator 6 and the output of the inverter 12 that inverts the phase of the output of the R-Y demodulator 6 are switched to the PAL switch 13.
The signal is output alternately every 1H to become the RY signal.

In the above configuration, the output of the 1H delay circuit 10
E _M (n-1) is expressed by the following equation similarly to equation (1).

E _M (n-1) = Y + Eusinωc (t-1/f _H ) + (-1) ⁿ Evcosωc (t-1/f _H )...(3) Therefore, the output of the subtraction circuit 11 E _M n-E _M (n-
1) becomes as shown in the following equation.

E _M n−E _M (n−1)=Eusinωct +(−1) ⁿ Evcosωct−Eusinωc(t−1/f _H ) −(−1) ⁿ Evcosωc(t−1/f _H ) ……(4) If we rearrange equation (4) using equation (2), we get the following equation.

E _M n−E _M (n−1) = {Eu+(−1) ⁿ Ev}√2sin(ωct+π/4)
(5) As is clear from equation (5), there is no luminance signal component in the output of the subtraction circuit 11, and the phases of the Eu and Ev components of the output of the subtraction circuit 11 match. Therefore, problems such as cross color do not occur, and unlike the conventional color demodulation circuit, two detection subcarrier signals having a phase difference of π/2 are generated, and the B-Y demodulator 5 and the R-Y There is no need to supply it to the demodulator 6, and both BY and RY signals can be obtained with a single subcarrier signal.

As described above, according to the present invention, since the luminance signal can be reliably removed and the color difference signal can be demodulated using a single demodulation axis, problems such as cross color can be prevented from occurring. At the same time, the circuit configuration can be simplified.

In the above embodiment, the RY signal was inverted after synchronous detection, but the RY signal is inverted by inverting the subcarrier of the RY component before synchronous detection. It is clear that it is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional color demodulation circuit, and FIG. 2 is a block diagram showing an embodiment of the present invention. Explanation of the symbols of the main parts, 2, 10... 1H delay circuit, 3... Addition circuit, 4, 11... Subtraction circuit,
5...B-Y demodulator, 6...R-Y demodulator, 12
...Inverter, 13...PAL switch.

Claims (1)

[Claims] 1. For a PAL color video signal in which one of the two carrier color signals each carrying two color difference signals and a color burst signal are phase-inverted every horizontal scanning period, based on the color burst signal. A color demodulation circuit in a video reproducing device that demodulates the carrier color signal using the obtained subcarrier, the signal delaying means delaying the luminance signal, the carrier color signal, and the color burst signal by a predetermined time;
a signal synthesizing means for synthesizing signals according to the difference between the input and output of the signal delaying means, and demodulating the two color difference signals included in the output of the signal synthesizing means, each using the subcarrier without phase adjustment. 1. A color demodulation circuit for a video reproducing device, comprising two demodulation means. 2. The color demodulation circuit for a video reproducing apparatus according to claim 1, wherein the predetermined time corresponds to one horizontal scanning period.