JPH099105A - Clamp strengthening circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a clamp strengthening circuit that does not cause unclamping even in the case of a noise signal having a large amplitude in a video signal processing circuit of a television receiver or the like. A low pass filter composed of a resistor 1, a capacitor 2 and the like is input to a Y signal input of a video signal processing circuit, and a transistor 3 is used by using any one signal of a flyback pulse, a sandcastle pulse and a horizontal synchronizing signal. Configuration with switching circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clamp circuit of a video signal processing circuit in video equipment such as a television receiver.

[0002]

2. Description of the Related Art Conventionally, in a television receiver,
It has a luminance signal clamp circuit for securing the pedestal level, a sharpness circuit, a color demodulation matrix, and R, G, B individual clamp circuits for securing the output pedestal level. FIG. 3 shows a video amplifier circuit of such a television receiver.

[0003]

When setting the clamp voltage, when the input signal is not a normal video signal but a noise signal which contains many high frequency components and the sync signal cannot be detected, the clamp voltage is set to the level of the input signal. It becomes the average voltage.

However, in such a conventional technique,
When using the sharpness circuit inside the video signal processing circuit,
The higher the sharpness, the larger the noise amplitude,
The clamp voltage is set high.

Therefore, when the clamp voltage exceeds the upper limit value of each clamp circuit, the clamp circuit causes the unclamping, and as a result, the R, G, B outputs of the video signal processing circuit are unbalanced and the white balance is lost. It had a problem of disturbing.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a clamp strengthening circuit which prevents the clamp from being disengaged even when the above noise signal is input to the luminance signal input.

[0007]

To achieve the above object, the present invention provides a low-pass filter that is switched by a flyback pulse, a sandcastle pulse, or a horizontal synchronizing signal at the luminance signal input of a video signal processing circuit, The clamp of each clamp circuit in the video signal processing circuit is strengthened by reducing the amplitude of the noise signal in the horizontal blanking period.

[0008]

According to the present invention, with the above-described structure, the clamp circuit operates stably even when a noise signal which contains a lot of high frequency components in the luminance input of the video signal processing circuit and which cannot detect the synchronizing signal is input. I can do things.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A clamp strengthening circuit according to an embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram of a clamp strengthening circuit according to a first embodiment of the present invention, and FIG. 2 is a block diagram of a clamp strengthening circuit according to a second embodiment of the present invention. In addition, in FIG. 2, parts corresponding to those in FIG.
Detailed description thereof will be omitted.

In FIG. 1, a resistor 1 is added to a signal input to a luminance signal (hereinafter referred to as Y signal) input of a video signal processing circuit.
A low-pass filter constituted by a capacitor 2 and the like causes the transistor 3 to be switched by a flyback pulse (hereinafter FBP), a sandcastle pulse (SCP) or a horizontal synchronization signal (HP).

As a result, by attenuating the high frequency component of the Y signal in the horizontal retrace line period, when noise is input, its amplitude is effectively reduced. FIG.
FIG. 4 is a diagram showing a correlation between a change state of a Y signal input waveform and any one of FBP, SCP, and HP.

In FIG. 2, a low-pass filter composed of a resistor 1, a capacitor 2 and the like is applied to the FBP or S for the signal input to the Y signal input of the video signal processing circuit.
By switching the transistor 3 with one of the signals CP or HP, the same function as in FIG. 1 is obtained.

[0013]

As described above, according to the present invention, by adding a low pass filter which is switched by any one of FBP, SCP or HP to the Y signal input of the video signal processing circuit, horizontal retrace By reducing the amplitude of the noise signal and reducing the average DC during the period, each clamp circuit in the video signal processing circuit can be strengthened.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a clamp strengthening circuit according to a first embodiment of the present invention.

FIG. 2 is a block configuration diagram of a clamp strengthening circuit according to a second embodiment of the present invention.

FIG. 3 is a block configuration diagram of a video signal amplifier circuit in a conventional television receiver.

FIG. 4 is a correlation diagram of a Y signal input waveform and a flyback pulse or the like.

[Explanation of symbols]

 1,4 Resistance 2,5 Capacitor 3 Transistor

Claims (1)

[Claims] 1. A clamp circuit for a luminance signal and a sharpness circuit are connected in series to a preceding stage of a video signal processing circuit, and any one signal of a flyback pulse, a sandcastle pulse or a horizontal synchronizing signal is transmitted. A clamp strengthening circuit for video equipment characterized by being used.