JPH01238394A - Signal demodulator - Google Patents

Abstract

PURPOSE:To make a horizontal blanking part noiseless with a signal demodulator which demodulates the carrier chrominance signal of television signals of a SECAM system by substituting prescribed potential for the horizontal blanking part of signals before and after a de-emphasis circuit. CONSTITUTION:Demodulated output of a demodulator circuit 2 are supplied to a de-emphasis circuit 4 through a switch 3. The output of the circuit 4 is outputted from an output terminal 7 as demodulated output signals (color difference signals) through a switch 5 and clamp circuit 6. The switches 3 and 5 respectively provided before and after the de-empahsis circuit 4 are switched by means of H pulses C whose period is one horizontal synchronizing period 1H and the horizontal blanking period HB of the signals is substituted by prescribed potential decided by a DC power source 8. Therefore, even if high noises exist in the horizontal blanking part HB of the demodulated outputs, the influence of the noises to the circuit 4 is eliminated and signals B having no noise in the horizontal blanking part HB are supplied to the clamp circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a signal demodulation device for demodulating a carrier color signal of a SECAM television signal.

B0 Summary of the Invention The present invention provides a signal demodulator for demodulating a carrier color signal of a SECAM television signal by replacing the horizontal blanking portion of the signal with a predetermined potential before and after a de-emphasis circuit. The influence of the de-emphasis circuit is eliminated, and the horizontal blanking section becomes noise-free, so clamping at any part of the horizontal blanking section will not result in a clamping error, making it possible to obtain good color balance. This is how it was done.

C1 Prior Art As a carrier color signal demodulation device used in a SECAM system television receiver, for example, Japanese Patent Application No. 1986-237
016 specification and the drawings are known. FIG. 4 is a block diagram showing the main structure of a conventional carrier color signal demodulation device. In FIG. 4, the carrier color signal (RY) or (B-Y) of the SECAM television signal supplied from the input terminal 101 is shown.
) is demodulated by the demodulation circuit 102, and then the demodulated output is sent to the clamp circuit 104 via the de-emphasis circuit 103.
The clamp circuit 104 performs a clamp operation using a clamp pulse, and the output terminal 105 outputs a demodulated output signal (color difference signal).

D1 Problems to be Solved by the Invention By the way, since the demodulated output from the demodulation circuit 102 includes a non-carrier part, a blanking noise component, etc., for example, as shown in FIG. 5(A), the horizontal blanking part There is large noise in HB. This noise does not disappear even after passing through the de-emphasis circuit 103, and as shown in FIG. 5(B), for example, the noise ends up trailing. If such a signal is clamped by a lamp pulse as shown in FIG. 5(E), for example, a clamping error will occur due to the influence of noise, and the color balance will be disrupted.

Therefore, as shown in FIG. 6, for example, a switch 106 is provided on the input side of the de-emphasis circuit 103 to replace the horizontal blanking portion HB of the demodulated output from the demodulation circuit 102 with a predetermined potential determined by the DC power supply 107. A demodulator has been proposed. Upper switch 1
06 is the horizontal synchronization period (I H
) is switched by an H pulse with a period of However, if the non-carrier portion (sink portion) of the signal shifts, the noise component will trail, for example, as shown in FIG. 5(C). In this case, it is possible to perform clamping in the latter half of the horizontal blanking part HB, but if it is performed in the first half, it will be affected by noise and cause a clamping error.
The color balance will be disrupted.

Therefore, the present invention was proposed in view of the above circumstances, and it makes the horizontal blanking part of the demodulated output noise-free, and clamps any part of the horizontal blanking part without causing a clamp error. It is an object of the present invention to provide a signal demodulation device that can obtain a good color balance without causing problems.

89 Means for Solving the Problems In order to achieve the above-mentioned object, a signal demodulation device according to the present invention includes a demodulation circuit that demodulates a carrier color signal of a SECAM television signal, and a demodulation output from the demodulation circuit. a de-emphasis circuit that performs de-emphasis processing;
a clamp circuit that clamps the output from the de-emphasis circuit; 1. The present invention is characterized in that replacement means for replacing the horizontal blanking portion of the signal with a predetermined potential is provided on the input side and the output side of the de-emphasis circuit, respectively.

F0 Effect According to the present invention, the influence of the de-emphasis circuit is eliminated, and the horizontal blanking portion becomes noise-free.

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

FIG. 1 is a block diagram showing a signal demodulation device in this embodiment. In this Figure 1, input terminal 1 has SEC
A carrier color signal (R-Y) or (B-Y) of an AM television signal is supplied and demodulated by the demodulation circuit 2. This demodulated output is passed through a switch 3 to a de-emphasis circuit 4 that performs de-emphasis processing on the demodulated output.
is supplied to The output from the de-emphasis circuit 4 is supplied to a clamp circuit 6 via a switch 5, and after being subjected to a clamp operation using a clamp pulse, is output from an output terminal 7 as a demodulated output signal (color difference signal). The switch 3.5 provided at the input end and the output side of the de-emphasis circuit 4 is switched by an H pulse whose cycle is a horizontal synchronization period (IH) as shown in FIG. The ranking portion HB is replaced with a predetermined potential determined by the DC power supply 8.

According to the signal demodulation device of this embodiment having such a configuration, even if there is large noise in the horizontal blanking portion HB of the demodulated output from the demodulation circuit 2, as shown in FIG. 2(A), for example, The horizontal blanking portions before and after the de-emphasis circuit 4 are replaced with a predetermined potential from the DC power supply 8, so that the influence of the de-emphasis circuit 4 is eliminated. As a result, the clamp circuit 6 has a second
A noise-free signal is supplied to the horizontal blanking portion HB as shown in Figure (B). Therefore, for example, in Figure 2 (D
), not only clamping by lamp pulses but also clamping at any part of the horizontal blanking portion HB will not cause clamping errors and good color balance can be obtained.

The switch 3.5 can be realized, for example, by a so-called Burton switch as shown in FIG. In FIG. 3, the emitters of differential transistor pair 11.12 are commonly connected to the collector of transistor 13, and the emitters of differential transistor pair 14.15 are commonly connected to the collector of transistor 16. The base of one of the transistors 13.16 is supplied with the H pulse shown in FIG. Differential transistor pair 11.12
The differential transistor pair 14 and 15 are turned on and off. As a result, a signal based on the input signal IN supplied to the base of the transistor 11 and a signal based on the input signal IN supplied to the base of the transistor 15 are selectively extracted from the emitter of the transistor 17 as the output signal OUT. It has become so.

H0 Effects of the Invention As is clear from the description of the embodiments described above, according to the present invention, the horizontal blanking portion of the signal is replaced with a predetermined potential before and after the de-emphasis circuit. The influence of the circuit is eliminated, and the horizontal blanking portion can be made noise-free. Therefore, clamping at any part of the horizontal blanking part does not cause a clamping error, and good color balance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the signal demodulation device according to the present invention, FIG. 2 is a waveform diagram for explaining the operation of the signal demodulation device of the above embodiment, and FIG. 3 is a signal demodulation device of the above embodiment. FIG. 3 is a circuit diagram showing an example of a switch in the demodulator. FIG. 4 is a block diagram showing an example of a conventional signal demodulation device,
FIG. 5 is a waveform diagram for explaining the operation of a conventional signal demodulating device, and FIG. 6 is a block diagram showing another example of the conventional signal demodulating device. 1... Input terminal 2... Demodulation circuit 3.5... Switch 4... De-emphasis circuit 6... Clamp circuit 7... Output terminal 8... DC power supply

Claims (1)

[Scope of Claims] A demodulation circuit that demodulates a carrier color signal of a SECAM television signal; a de-emphasis circuit that performs de-emphasis processing on the demodulated output from the demodulation circuit; and a de-emphasis circuit that clamps the output from the de-emphasis circuit. A signal demodulator comprising: a clamp circuit; and replacement means for replacing a horizontal blanking portion of a signal with a predetermined potential are provided on the input side and the output side of the de-emphasis circuit, respectively.