JPH051678B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a color demodulation circuit for a video reproduction 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.

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

E _Mo = Y + E _U sinω _ct + (-1) ⁿ E _V cosω _ct ...(1) ω _c =2πf _H (m-1/4) ...(2) Here, Y is the luminance signal, E _U and _EV indicates color difference signals B-Y and RY, 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) ⁿ in equation (1) means phase inversion for each horizontal scanning line, and the E _V component of the carrier color signal has a phase difference of 180° from each other for each horizontal scanning line. (-1) ⁿ cosω _ct is transmitted by balanced modulation of the subcarrier signal. Therefore, the color burst signal is required to have information for inverting the phase of the _EV component subcarrier line by line on the image receiving side. For this reason, the color burst signal is switched line by line to a phase of ±135° around the _EU axis, and the phase-inverted signal 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 Figure 1,
When a carrier color signal included in a PAL color video signal is transmitted along with a color burst signal, delay circuits 1 and 2, adder circuits 3 and 4,
The signal is supplied to the subtraction circuit 5 and the burst gate 6.
The signal delay time in the 1H delay circuit 1 is set to be longer or shorter than 1H by (π/2)×(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 carried color signal is accurately 1H.
Although it has a phase difference of π/2 from the previous phase,
The phase of the carrier color signal outputted from the 1H delay circuit 1 about 1H earlier almost matches the phase of the input signal. The output of this 1H delay circuit 1 is supplied to an addition circuit 3 and a subtraction circuit 5. In the adder circuit 3,
When the output of 1H delay circuit 1 is added to the carrier color signal, the E _V component of the carrier color signal is canceled and E _U
Only the components are output from the adder circuit 3. In addition, in the subtraction circuit 5, for example, 1H
By subtracting the output of the delay circuit 1, the _EU component of the carrier color signal is canceled and only the _EV component is output from the subtracting circuit 5. These adder circuits 3
and the outputs of the subtraction circuit 5 are sent to the B-Y demodulator 7, respectively.
and RY demodulator 8, respectively.

The burst gate 6 includes a pulse generator (not shown) configured to delay the horizontal synchronization signal and output a gate pulse while the color burst signal is present, for example.
output is also provided. Burst gate 6 is
For example, it consists of an analog switch circuit that turns on and off depending on the output of this pulse generator. After the color burst signal is separated and extracted from the carrier color signal by this burst gate 6, the APC (Auto
The signal is supplied to a subcarrier generator 9 based on the 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 this subcarrier generator 9 is passed through a 90° phase shifter 10.
B-Y as subcarrier for test liquid with 90° phase shift
The signal is supplied to a demodulator 7. In addition, this color subcarrier signal is transferred to a 180° phase shifter 1 that shifts the input phase by 180°.
1 and PAL switch 12.
The output of the burst detection circuit 13 is supplied to the PAL switch 12 as a phase discrimination signal.
The output of the burst detection circuit 13 is supplied to the PAL switch 12 as a phase discrimination signal.
The operation of the PAL switch 12 is reset by a phase discrimination signal, and the PAL switch 12 is configured to selectively output one of the color subcarrier signal and the output of the 180° phase shifter 11 alternately every 1H. .
The 12 outputs of this PAL switch are supplied to the RY demodulator 8 as detection subcarriers.

The burst detection circuit 13 is provided by adding and synthesizing the addition output from the adder circuit 4, that is, the carrier color signal and color burst signal, and the output of the 1H delay circuit 2, which delays these carrier color signals and color burst signals by exactly 1H. signal is being supplied. The burst detection circuit 13 is configured to perform envelope detection on the output of the addition circuit 4, for example, and selectively output pulses generated in the color burst existing section.

In the above configuration, 1H is generated along with the carrier color signal.
The phase of the color burst signal supplied to the delay circuit 2, adder circuit 4, etc. during consecutive 4H is the second
It is shown in Figures A to D. As is clear from FIGS. 4A to 4D, the color burst signal is
-The phase is switched to ±135° around the Y axis every 1H, and the inverted phase is sent out.In addition, in order to prevent vertical stripe interference, continuous Since 1/4 line offset is adopted in which the phase of the subcarrier is shifted by 90° between two scanning lines, 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
The portion corresponding to the color burst signal in the output of the adder circuit 4 which adds the signal obtained by delaying by 1H is canceled every 2H. When the output of the adder circuit 4 is supplied to the burst detection circuit 13, a pulse as a phase discrimination signal generated by envelope detection is generated every 2H in the burst detection circuit 13. Therefore, even if the inverting operation of the subcarrier signal by the PAL switch 12 is reversed, the inverting operation returns to normal within 2H, allowing high-speed response.

Since the conventional color demodulation circuit as described above requires two delay circuits, it has the disadvantage of increasing the circuit scale and high manufacturing cost.

SUMMARY OF THE INVENTION 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 input 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 shift state of the color burst signal is discriminated by a composite signal obtained by adding or subtracting the inputs of the color burst signal and the signal delay means, and a subcarrier signal for demodulation is generated.

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

In Fig. 3, 1H delay circuit 1, adder circuit 3,
4, subtraction circuit 5, burst gate 6, B-Y demodulator 7, R-Y demodulator 8, subcarrier generator 9,
The 90° phase shifter 10, the 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 1H delay 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, if the delay time of the 1H delay circuit 1 is longer than 1H by (π/2)×(1/ωc), the 90° phase shifter 14 is designed to advance the input phase by 90°. and 1H delay circuit 1
If the delay time of is shorter than 1H by (π/2)×(1/ωc), the input phase is changed as
A material with characteristics such as a delay of 90° shall be used. Then, the carrier color signal and color burst signal delayed by exactly 1H are output from the 90° 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 2H, so the portion corresponding to the color burst signal in the output of the adder circuit 4 is canceled every 2H, similar to the circuit shown in Fig. 1. Become. The output of this adder circuit 4 is supplied to the burst detection circuit 13 in the same way as the circuit shown in FIG.
Even if the inversion operation of the subcarrier signal by the PAL switch 12 is reversed, the inversion operation returns to normal within 2H, allowing high-speed response.

Note that 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 1H delay circuit 2 is supplied to the burst detection circuit 13.

Effects of the Invention As detailed above, the color demodulation circuit of the video reproducing apparatus according to the present invention includes phase shifting means for shifting the phase of the output of the signal delaying means for delaying the carrier color signal and the color burst signal by a predetermined phase. Since the phase state of the color burst signal is discriminated by the composite signal obtained by adding or subtracting the output of the transfer means and the input of the signal delay means, a high-speed response is possible and the channel This makes it possible to prevent color disturbances due to switching or the like. At the same time, the 1H delay circuit for separating E _U and _EV components and the 1H delay circuit for phase discrimination of color burst signals can be used in common.
This means that the circuit scale can be reduced and manufacturing costs can be reduced.

[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 4Hs, and FIG. 3 is a diagram showing a color burst signal according to the present invention. FIG. 2 is a block diagram showing an embodiment. Explanation of symbols of main parts, 1...1H delay circuit,
3, 4... Addition circuit, 5... Subtraction circuit, 12...
PAL switch, 13... Burst detection circuit, 1
4...90° phase shifter.

Claims (1)

[Claims] 1. In a video reproducing device that reproduces video using a PAL color video signal, a signal delaying means for delaying a carrier color signal and a color burst signal included in the PAL color video signal by a predetermined time, and an input and an output of the signal delaying means. and a second signal synthesizing means for synthesizing a signal according to the difference between the input and output of the signal delaying means, each of the outputs of the first and second signal synthesizing means. A color demodulation circuit configured to demodulate two color difference signals respectively included in the signal delaying means, the circuit comprising: a phase shifting means for shifting the phase of the output of the signal delaying means by a predetermined phase; A color demodulation circuit for a video reproducing apparatus, characterized in that the phase state of the color burst signal is discriminated by a composite signal obtained by adding or subtracting the outputs of the phase shifting means to generate a subcarrier signal for demodulation.