JP2545781B2 - Signal demodulation circuit - Google Patents

Description

The present invention relates to a signal demodulation circuit applied to a SECAM type television receiver.

[Outline of Invention]

The present invention is SECA in which two color signals are line-sequentially FM-transmitted.
In the signal demodulation circuit that demodulates the M system television signal, the signal level of the unmodulated carrier part of the demodulation signal is compared with the reference voltage on the preceding side of the de-emphasis circuit, and the error voltage is used as the phase shift amount control signal. By performing feedback control of the phase shift characteristics of the phase shifter, a stable color balance of the demodulation output is ensured and the discriminator can be adjusted without adjustment.

[Conventional technology]

Generally, in a signal demodulator for demodulating a SECAM type television signal, a carrier color signal is extracted from an input SECAM signal supplied to an input terminal 1 by a bell filter 2 as shown in FIG. By switching the signal passing through and the signal not passing through for each scanning line by the line switch 4, the synchronous conversion is sequentially performed, and the two color difference signals (RY) and (BY) are taken out, and the demodulation circuits 5 and 6 respectively.
The FM demodulation is performed and the three color difference signals (RY), (BY), and (GY) are output from the color difference matrix 7.

As the demodulation circuits 5 and 6, the circuit configuration shown in FIG. 5 has been conventionally used.

In this conventional example, the SECAM type carrier color signal is
Multiplier 12 and phase shifter 13 from input terminal 10 through limiter 11
Is supplied to In the multiplier 12, the limiter 11
The color difference signal is demodulated by multiplying the signal directly supplied from the signal and the signal which is phase-shifted by 90 ° in the phase shifter 13. The color difference signal demodulated by the multiplier 12 is supplied to the de-emphasis circuit 16 via the switch 14. The output signal of the de-emphasis circuit 16 is
It is supplied to the clamp circuit 18 through the color saturation control circuit 18, and the clamp circuit 18 clamps the unmodulated carrier portion and outputs it from the output terminal 19.

Here, in the SECAM type carrier color signal supplied to the input terminal 10, as shown in FIG. 6, since the non-modulation carrier portion A is present before the non-modulation carrier portion A, the multiplier 12 When demodulated, the demodulated output of the carrierless portion B becomes a noise component. When the demodulation output by the multiplier 12 passes through the de-emphasis circuit 16, the demodulation level of the unmodulated carrier portion A fluctuates due to the influence of the noise component, and an error occurs even if this portion is clamped. Therefore, in the conventional demodulation circuit, the demodulation output by the multiplier 12 is supplied to the de-emphasis circuit through the switch 14 that selects the multiplier 12 and the DC power supply 15, and the horizontal output of the demodulation output is obtained. The ranking part was clamped by replacing it with the DC potential.

[Problems to be solved by the invention]

By the way, in the conventional signal demodulating circuit having the above-mentioned configuration, the horizontal blanking portion of the demodulated signal of the carrier color signal of the SECAM system is clamped by replacing it with the DC potential. If the center is not matched, faithful signal demodulation cannot be performed, it takes time and effort to adjust the phase shift characteristics of the phase shifter, and the fluctuation of the phase shift characteristics due to the temperature change of the phase shifter. Has a problem that it affects the color balance.

Therefore, in view of the above-mentioned problems, the present invention aims to provide a signal demodulation circuit having a novel configuration that secures a stable color balance of demodulation output and enables no adjustment of the discriminator. It is what

[Means for solving problems]

In order to solve the above-mentioned problems, the signal demodulation circuit according to the present invention supplies a variable phase shifter whose phase shift characteristic can be externally controlled and a demodulated input signal directly or via a color saturation control circuit. And a color saturation control circuit that variably controls the color saturation of the demodulation signal by the multiplier in the preceding stage or the latter stage of the multiplier, and the color saturation. The de-emphasis circuit to which the demodulation signal whose color saturation is variably controlled by the degree control circuit is supplied, and the signal level of the non-modulated carrier part of the demodulation signal input to the de-emphasis circuit is compared with the reference voltage,
The error voltage is sampled and held, and the sample and hold output is used as a phase shift amount control signal to feedback control the phase shift amount of the variable phase shifter. It is characterized in that the phase variation is absorbed by the feedback control of the phase shift amount.

[Action]

In the signal demodulation circuit according to the present invention, the variable phase shifter gives the demodulated input signal a 90 ° phase shift amount at the carrier frequency, and the demodulated input signal and the 90 ° phase shift amount are demodulated. The demodulation signal obtained by multiplying the input signal by the multiplier is variably controlled by the color saturation control circuit in the previous stage or the subsequent stage of the multiplier, and is supplied to the de-emphasis circuit. The sample and hold circuit compares the signal level of the unmodulated carrier part of the demodulated signal input to the de-emphasis circuit with the reference voltage, samples and holds the error voltage, and outputs the sample and hold output as the phase shift amount. As a control signal, feedback control is performed so that the phase shift amount of the variable phase shifter becomes 90 ° at the carrier frequency.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

In the first embodiment shown in FIG. 1, the signal input terminal 20
The carrier color signal of the color difference signal (RY) obtained by sequentially performing synchronous conversion by the line switch in the above-mentioned general SECAM system signal demodulating device is supplied to.

The carrier color signal is supplied to the color saturation control circuit 22 and the variable phase shifter 23 via the limiter 21.
The variable phase shifter 23 phase-shifts the carrier color signal supplied from the limiter 21 by 90 ° and supplies it to the multiplier 25. And
The multiplier 25 is supplied with the output signal of the color saturation control circuit 22, and multiplies this signal by the carrier color signal whose phase is shifted by 90 ° to demodulate the color difference signal (RY).

The demodulated output signal from the multiplier 25, that is, the color difference signal (RY) is supplied to the sample and hold circuit 26 and the color difference matrix circuit (not shown) through the de-emphasis circuit 27.

The sample and hold circuit 26 samples the demodulation output level of the unmodulated carrier portion of the input SECAM signal and compares it with a reference voltage, and holds an error voltage to the variable phase shifter 23 as a phase shift amount control signal. By feeding back, the variable phase shifter 23 is controlled so that the phase shift amount of the variable phase shifter 23 becomes 90 ° at the carrier frequency of the color difference signal (RY).

Here, the portions of the sample and hold circuit 26 and the de-emphasis circuit 27 are realized by a circuit configuration as shown in FIG. 2, for example.

That is, in FIG. 2, the demodulated output signal from the multiplier 25 is passed through the emitter follower of the transistor 31 and the transistor constituting the sample and hold circuit 26.
It is supplied to the base of one of 32 and 33, and the resistance of 34 and 35
And de-emphasis circuit 2 composed of capacitors 36 and 37
Supplied to 7.

The pair of transistors 32, 33 compares the reference voltage Vref applied to the other base with the signal level of the demodulated output signal, and the switching operation of the switch 38 connected to its emitter causes the unmodulated carrier described above. The error voltage of a part is sampled and held in the capacitor 39. Then, the held error voltage is output as the above-mentioned phase shift amount control signal via the Darlington transistors 40 and 41.

In this embodiment, the color difference signal (RY) demodulated by the multiplier 25 to which the carrier color signal 90 ° phase-shifted by the variable phase shifter 23 subjected to the feedback control as described above is supplied.
Means that the signal level of the unmodulated carrier portion is clamped by the feedback control, and the phase is changed even if the phase is changed by changing the color saturation in the color saturation control circuit 22 in the previous stage. Since the fluctuation amount of is absorbed by the clamp by the feedback control, an extremely stable white balance can be secured even if the discriminator is not adjusted.

In the first embodiment described above, the color saturation control circuit 22
Is arranged before the multiplier 25. However, as shown in the second embodiment shown in FIG. 3, the multiplier 25 and the de-emphasis circuit 27 are provided.
The color saturation control circuit 22 may be disposed between and.

〔The invention's effect〕

As is clear from the above description of the embodiments, in the signal demodulating device according to the present invention, the signal level of the non-modulated carrier portion of the demodulated signal is sampled and compared with the reference voltage on the upstream side of the de-emphasis circuit, By holding the error voltage and feedback-controlling the phase shift characteristic of the variable phase shifter by using this hold output as a phase shift amount control signal, the variable phase shifter gives a phase shift amount of 90 ° at the carrier frequency. Since it operates, even if the phase changes by changing the color saturation degree by the color saturation degree control circuit before or after the multiplier that supplies the demodulation signal to the de-emphasis circuit, the phase variation is controlled by the feedback control. It is possible to ensure stable color balance of the demodulated output and to make the discriminator non-adjustable.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a signal demodulation circuit according to the present invention, and FIG. 2 shows a concrete circuit configuration example of a sample hold circuit and a de-emphasis circuit portion in the above embodiment. It is a circuit diagram. FIG. 3 is a block diagram showing a second embodiment of the signal demodulation circuit according to the present invention. FIG. 4 is a block diagram showing the configuration of a general SECAM type signal demodulation device. FIG. 5 is a block diagram showing a conventional example of a signal demodulation circuit, and FIG. 6 is a waveform diagram showing an operation of the conventional example. 23: Variable phase shifter 25: Multiplier 26: Sample and hold circuit 27: De-emphasis circuit

Claims (1)

(57) [Claims] 1. A variable phase shifter having externally controllable phase shift characteristics, and a multiplication in which a demodulated input signal is supplied directly or via a color saturation control circuit and is also supplied via the variable phase shifter. And a color saturation control circuit for variably controlling the color saturation of the demodulation signal by the multiplier in the preceding stage or the latter stage of the multiplier, and the demodulation signal whose color saturation is variably controlled by the color saturation control circuit. The supplied de-emphasis circuit and the signal level of the non-modulated carrier part of the demodulated signal input to the de-emphasis circuit are compared with the reference voltage, the error voltage is sampled and held, and the sample and hold output is transferred. A sample-and-hold circuit for feedback controlling the phase shift amount of the variable phase shifter as a phase amount control signal. Signal demodulation circuit, characterized in that the absorption Te.