JPS61144186A - Chrominance demodulating circuit of video reproducing device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of disorder of colors due to external disturbance by discriminating the state of phase of a color burst signal by a synthesizing signal of a delay signal and phase shifting signal of a carrier chrominance signal and a color burst signal. CONSTITUTION:The chrominance demodulating circuit of a video reproducing device consists of a 1H delay circuit 1, adder circuits 3, 4, a subtracter circuit 5, a burst gate 6, a B-Y demodulator 7, and R-Y demodulator 8, a subcarrier generator 9, a 90 deg. phase shifter 10, a 180 deg. phase shifter 11, a PAL switch 12 and a burst detecting circuit 13. Further, output of the 1H delay circuit is supplied to a 90 deg. phase shifter 14. A carrier chrominance signal and a color burst signal are added and composed to output of the 90 deg. phase shifter in the adder circuit 4. Output of the adder circuit 4 is supplied to the burst detecting 13. Accordingly, even when inversion action of a subcarrier signal by the PAL switch 12 is reversed, the inversion action is restored to normal in 2H. Thus, high speed response is made possible, and occurrence of disorder of colors due to channel changing can be prevented.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a color demodulation circuit for a video reproduction device, and in particular to a color demodulation circuit for a video reproduction device.
L (Phase Alternative.

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 N-Line system.

A PAL color video signal EMo corresponding to a scanning line of 9 and 51 n (n is a natural number) grain is given by the following equation.

E = Y + E US i nωctn + (-1)0Evcosω. t...(1) ω. -2πfH (m-174) (2) Here, Y is a luminance signal, E and E are color difference signals B-Y, R
-Y are shown respectively. Note that B and R indicate blue and red signals, respectively. Further, f+ is a horizontal scanning frequency, and m is a natural number.

The coefficient (-1) n in equation (1) means a phase inversion for each horizontal scanning line, and the E acid component of the conveyed color signal has a phase difference of 180° from each other for each horizontal scanning line. <-i)
'cosω. It is transmitted by balanced modulation of the subcarrier signal t. Therefore, the color burst signal is required to have information for inverting the phase of the E2 acid component subcarriers 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 for a device that reproduces video using PAL color video signals, which was devised by the inventors and is capable of high-speed response. In FIG. 1, a carrier color signal included in a PAL color video signal is transmitted along with a color burst signal to 1H (one horizontal scanning period) delay circuits 1, 2, . Addition circuit 3,
4, is supplied to the subtraction circuit 5 and the burst gate 6. 1
The signal delay time in the day delay circuit 1 is (π/
2) The time is set to be longer or shorter by X(1/ωC). Therefore, in order to prevent 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 accurately the same as the phase 1H before. Although there is a shift of π/2, the phase of the carrier color signal outputted from the one-day delay circuit 1 about one to one earlier almost matches the phase of the input. The output of this one-day delay circuit 1 is supplied to an addition circuit 3 and a subtraction circuit 5. In the adder circuit 3, when the output of the one-day delay circuit 1 is added to the carrier color signal, the Ev acid component of the carrier color signal is canceled and only the EU acid component is added to the adder circuit 3.
is output from. Further, in the subtraction circuit 5, for example, the output of the one-day delay circuit 1 is subtracted from the carrier color signal, thereby canceling out the EU acid component of the carrier color signal.
Only the acid component is output from the subtraction circuit 5. The outputs of the addition circuit 3 and subtraction circuit 5 are supplied to a BY demodulator 7 and an RY demodulator 8, respectively.

The burst gate 6 is also supplied with the output of a pulse generator (not shown) configured to delay the horizontal synchronizing signal and output a gate pulse while the color burst signal is present, for example. The burst gate 6 is composed of an analog switch circuit that is turned on and off depending on the output of this pulse generator, for example. After the color burst signal is separated and extracted from the carrier color signal by the burst gate 6, the APC (A
The signal is supplied to a subcarrier generator 9 based on the Auto Phase Control method. The subcarrier generator 9 is configured to generate a color subcarrier signal having a predetermined phase difference from the color burst signal. The color subcarrier signal output from the subcarrier generator 9 is phase-shifted by 90° by a 90° phase shifter 10 and is supplied to the B-Yla device 7 as a subcarrier for detection. In addition, this color subcarrier signal has an input of 1
It is also supplied to a 180° phase shifter 11 that shifts the phase by 80° and a PAL switch 12. The output of the burst detection circuit 13 is supplied to the PAL switch 12 as a phase discrimination signal. The PAL switch 12 has a burst detection circuit 13.
The output of is supplied as a phase discrimination signal. The operation of the PAL switch 12 is reset by the phase discrimination signal, and the operation is reset by the color subcarrier signal and the 180° phase shifter 11.
It is configured to alternately and selectively output one of the outputs every 1H. Twelve outputs of this PAL switch are supplied to the RY demodulator 8 as subcarriers for detection.

The burst detection circuit 13 outputs the addition output from the adder circuit 4, that is, the carrier color signal and color burst signal, and delays the carrier color signal and color burst signal by exactly one day! ! A signal obtained by adding and combining the output of the extension circuit 2 is supplied.

The burst detection circuit 13 is configured to, for example, perform envelope detection on the output of the addition circuit 4 and selectively output pulses generated in the color burst existing section.

In the above configuration, the phase of the color burst signal supplied to the 1H delay circuit 2, adder circuit 4, etc. along with the carrier color signal during four consecutive days is shown in FIGS. 2(A) to 2(D).
) is shown. As is clear from FIGS. 4(A) to 4(D), the color burst signal is switched to a phase of ±135° around the B-Y axis every day, and the phase-inverted signal is sent out. In addition to this, in order to prevent vertical stripe interference, a 1/4 line offset is adopted in which the subcarrier phase is shifted by 90° between two consecutive scanning lines in the same field. Therefore, the phase of the color burst signal is inverted every 2H. Therefore, the carrier color signal and color burst signal and the carrier color signal and color burst signal can be accurately IHil! The portion corresponding to the color burst signal in the output of the adding circuit 4 which adds the signal obtained by extending the color burst signal is canceled out every two days. When the output of the adder circuit 4 is supplied to the burst detection circuit 13, the burst detection circuit 13 generates every 211 pulses as a phase discrimination signal generated by envelope detection. Therefore, PAL
Even if the inversion operation of the subcarrier signal by the switch 12 is reversed, the inversion operation will return to normal within 2H.
High-speed response is possible.

Since the conventional color demodulation circuit as described above requires two delay circuits, it has the disadvantage that the circuit scale becomes large and the manufacturing cost is high.

An object of the present invention is to provide a color demodulation circuit for a video reproducing device that is capable of high-speed response, has a small circuit scale, and is inexpensive.

The color demodulation circuit of the video reproducing apparatus according to the present invention includes: a signal delaying means for delaying a carrier color signal and a color burst signal by a predetermined time; a first signal synthesizing means for adding and synthesizing the input and output of the signal delaying means; a second signal synthesizing means for synthesizing a signal according to the difference between the power and output of the means, and a phase shifting means for shifting the phase of the output of the signal delaying means by a predetermined phase, the phase shifting means The phase shift state of the color burst signal is discriminated by a composite signal obtained by adding or subtracting the output of the color burst signal and the input of the signal delay means to generate a subcarrier signal for demodulation.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIG. 3.

In Fig. 3, one day delay circuit 1, addition circuit 3゜4, subtraction circuit 5, burst gate 6, B-YIIE circuit 7, R
-Y demodulator 8, subcarrier generator 9°90” phase shifter 1
The 0.180° phase shifter 11, the PAL switch 12, and the burst detection circuit 13 are connected in the same way as the circuit shown in FIG. However, in this example, the output of the IHI extension circuit 1 is supplied to the 90@phase shifter 14. The output of the 90° phase shifter 14 is added and combined with the carrier color signal and the color burst signal in the adder circuit 4.

In the above configuration, the delay time of the one-day delay circuit 1 is 1H.
90° if it is longer than (π/2)X(1/ωC)
If a phase shifter 14 with characteristics that advances the input phase by 90° is used, and if the delay time of the one-day delay circuit 1 is shorter than one day by (π/2)×(1/ωC), °
Assume that the phase shifter 14 has a characteristic that shifts the input phase by 90"iI. Then, 90"
The carrier color signal and color burst signal delayed by exactly one day are output from the phase shifter 14 and supplied to the adder circuit 4. As a result, as shown in Fig. 2, the phase of the color burst signal is inverted every 2 days, so the portion corresponding to the color burst signal in the output of the adder circuit 4 is canceled out every 2 days, similar to the circuit shown in Fig. 1. Become. The output of the adder circuit 4 is supplied to the burst detection circuit 13 in the same way as the circuit shown in FIG. , high-speed response becomes possible.

Incidentally, a subtraction circuit may be used in place of the addition circuit 4 in the above embodiment so that a signal corresponding to the difference between the input and output of the 1HM extension circuit 2 is supplied to the burst detection circuit 13.

λ1 Rikko 1 As detailed above, the color demodulation circuit of the video reproducing apparatus according to the present invention has a phase shifter that shifts the phase of the output of the signal delay means for delaying the carrier color signal and the color burst signal by a predetermined phase. The phase state of the color burst signal is discriminated by a composite signal obtained by adding or subtracting the output of the phase shifting means and the input of the signal delaying means, so that a high-speed response is possible. This makes it possible to prevent color disturbances from occurring due to channel switching or the like. Moreover, at the same time, the 1HN extension circuit for separating the EE components U and V and the 1H''i1 extension circuit for phase discrimination of the color burst signal can be used in common, reducing the circuit scale and manufacturing cost. will be possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional color demodulation circuit, FIG. 2 is a vector diagram of carrier color signals and color burst signals for each 1H during consecutive 41 periods, and FIG. 3 is an embodiment of the present invention. FIG. 2 is a block diagram illustrating an example. Explanation of symbols of main parts 1...1H delay circuit 3.4...Addition circuit 5...Subtraction circuit 12...PAL switch 13... ...Burst detection circuit 14...90° phase shifter

Claims (1)

[Claims] In a video reproducing apparatus that reproduces video using a PAL color video signal in which one of the carrier color signals and the color burst signal are phase-inverted every horizontal scanning period, a signal delay that delays the carrier color signal and the color burst signal by a predetermined time. means, first signal synthesizing means for adding and synthesizing the input and output of the signal delaying means, and second signal synthesizing means for synthesizing a signal according to the difference between the input and output of the signal delaying means, A color demodulation circuit configured to demodulate two color difference signals included in each of the outputs of the first and second signal combining means, the phase shifting circuit shifting the phase of the output of the signal delaying means by a predetermined phase. means for discriminating the phase state of the color burst signal using a composite signal obtained by adding or subtracting the input of the signal delay means and the output of the phase shift means to generate a subcarrier signal for demodulation. color demodulation circuit for video playback equipment.