JPH02280574A - Video signal circuit - Google Patents

Abstract

PURPOSE:To prevent deterioration in picture quality by inputting a video signal superimposed with a triangle wave, generating a triangle wave signal synchronously with the triangle wave, using a differential amplifier to eliminate the triangle wave and setting a level of a pulse tip of a horizontal synchronizing signal to a fixed level with a clamp circuit. CONSTITUTION:In order to generate a triangle wave signal synchronously with. a triangle wave of a video signal A inputted from an input terminal 2 and superimposed with the triangle wave, a comparator 1 compares a reference voltage Vref with the video signal A to form a pulse signal B. A triangle wave generating circuit 4 generates a triangle wave signal C with the same phase as that of the triangle wave superimposed on the video signal A synchronously with the pulse signal B generated from the comparator 1. A differential amplifier 5 receives the video signal A at its noninverting input terminal and outputs a shape signal D resulting from the video signal A superimposed with the triangle wave signal subtracted from the triangle wave. Thus, the capacity of a coupling capacitor at the input of a clamp circuit 7 is increased independently of the capability of eliminating a triangle wave of the clamp circuit.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a video signal circuit.

[Conventional technology]

Conventionally, a video signal circuit that receives satellite broadcasting and removes a 15 Hz triangular wave signal superimposed on the video signal to spread the energy of the video signal by the satellite broadcasting has an input signal as shown in FIG. It has a circuit configuration in which the terminal 2 and the clamp circuit 7 are coupled by a coupling capacitor 6, and the horizontal synchronizing signal pulse tip (
The triangular wave signal was removed by aligning the levels of the sync chips (hereinafter referred to as sync chips).

[Problem to be solved by the invention]

In the conventional video signal circuit described above, the triangular wave signal removal ability changes depending on the capacitance of the coupling capacitor connected to the input end of the clamp circuit to remove the triangular wave signal, and the capacitance of the coupling capacitor is also a problem for video signals. becomes. That is, as shown in Fig. 5, when the capacitance of the coupling capacitor is reduced in order to remove the triangular wave signal, the low frequency range of the video signal is attenuated, a tilt occurs in the video signal, and the image quality is reduced as shown in the output video signal E2. deteriorates. −
On the other hand, if the capacitance of the coupling capacitor is increased, the video signal will not be distorted, but the clamp circuit will not be able to remove the triangular wave signal like the output video signal E, causing fluctuations in the screen and deteriorating the image quality.

[Means to solve the problem]

The video signal circuit of the present invention includes a triangular wave generating circuit which inputs a video signal on which a triangular wave is superimposed and forms a triangular wave signal synchronized with the triangular wave, and which inputs the video signal and the triangular wave signal and processes the triangular wave signal. It has a differential amplifier that removes the triangular wave from the video signal, and a clamp circuit that inputs the output of the differential amplifier via a coupling capacitor and sets the level of the tip of the horizontal synchronizing signal pulse of the video signal to a fixed potential. .

〔Example〕

Next, the present invention will be explained with reference to the drawings.

1 and 2 are a block diagram and a waveform diagram showing a first embodiment of the present invention.

As shown in FIGS. 1 and 2, a comparator 1 receives a video signal A input from an input terminal 2 on which a triangular wave is superimposed.
In order to generate a triangular wave signal synchronized with the triangular wave, a pulse signal B is generated by comparing the reference voltage V r e r with a video signal A in which the triangular waves are superimposed. The triangular wave generating circuit 4 generates a triangular wave signal C having the same phase as the triangular wave superimposed on the video signal A in synchronization with the pulse signal B generated by the comparator 1. The differential amplifier 5 inputs the video signal A to its non-inverting input terminal, and outputs a shaped signal obtained by removing the triangular wave from the video signal A on which the triangular wave is superimposed. The shaped signal is input to a clamp circuit 7 via a capacitor 6 which cuts off the DC component and has a capacitance value sufficient for the video signal to pass through, and is clamped by the clamp circuit 7 set to a clamp voltage VC to output the video signal. Get E.

FIG. 2 is a block diagram showing a second embodiment of the invention.

It has the same configuration as the first embodiment except that the low-pass filter 8 extracts only the triangular wave component from the video signal A on which the triangular wave is superimposed, and the differential amplifier 5 removes the triangular wave component superimposed on the video signal. Although the removal ability is lower than that of the first embodiment, it has the advantage of simplifying the circuit.

〔Effect of the invention〕

As explained above, in order to remove the triangular wave before the video signal superimposed with the triangular wave is input to the clamp circuit, the present invention relates the capacitance of the coupling capacitor at the input of the clamp circuit to the triangular wave removal ability of the clamp circuit. Capacity can be increased without any problems.

Therefore, there is an effect that signal processing can be performed without attenuating the low frequency range of the video signal.

Oscillator, 5... Differential amplifier, 6... Coupling capacitor, 7... Clamp circuit, 8... Low pass filter, A... Input video signal, B... Pulse signal, C
...triangular wave signal, D...shaped signal, E, E,, E2
...Output video signal, Vr*t...Reference voltage.

Claims (1)

[Claims] a triangular wave generation circuit that inputs a video signal on which a triangular wave is superimposed and forms a triangular wave signal synchronized with the triangular wave;
a differential amplifier which receives and processes the video signal and the triangular wave signal and removes the triangular wave from the video signal; and a horizontal synchronization signal of the video signal which inputs the output of the differential amplifier via a coupling capacitor. A video signal circuit comprising: a clamp circuit that sets the level of a pulse tip to a fixed potential.