JPH07212670A - Gain control circuit - Google Patents

Abstract

PURPOSE:To reduce the gain control adjustment in a factory and to attain stable gain. CONSTITUTION:The control circuit is made up of a reference signal generator 9 generating a reference signal for a stable gain and no adjustment, a timing pulse generator deciding an output timing of the reference signal, an amplifier 3 adjusting a gain of an output of a mixing circuit 2 inserting the reference signal to a video signal in said output timing, a circuit 4 driving a cathode of a CRT 10, a detector 6 detecting he reference signal from the circuit 4, an integration device 7 applying DC transformation to a detected signal, and a comparator 8 comparing the integrated signal with a voltage of the reference signal generator 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal gain control circuit for a television receiver, a commercial monitor receiver and the like.

[0002]

2. Description of the Related Art A gain control circuit for a conventional television receiver or commercial monitor receiver will be described below. FIG. 4 is a block diagram showing a conventional gain control circuit. In FIG. 4, 1 is a signal input unit, 12 is a gain adjusting unit, 3 is an amplifier, 4 is a circuit for driving the cathode of a CRT, and 10 is a CR.
At T, they are sequentially connected. Reference numeral 13 is a factory adjustment volume for changing the gain adjustment unit 12, and 14 is a user gain adjustment volume for changing the gain of the amplifier 3.

The operation of this gain control circuit will be described below. First, a video signal is input from the signal input unit 1,
It is output to the tube surface of the CRT 10 via the gain adjusting unit 12, the amplifier 3, and the circuit 4 that drives the cathode of the CRT. For adjusting the gain of the video signal, the gain adjusting unit 12 is set to the factory adjustment volume 13 so that the drive circuit 4 has a predetermined signal level.
It is done by adjusting in. This adjusted video signal is fed through the amplifier 3 to the user gain adjustment volume 1
By varying with 4, the user can adjust the gain of the received signal according to his or her preference.

[0004]

However, in the above conventional configuration, it is necessary to adjust the factory adjustment volume to suppress the fluctuation of the video signal gain due to the fluctuation of the components of each circuit system itself. The adjustment man-hours of was indispensable.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a gain control circuit capable of reducing the number of gain control adjustment steps and supplying a stable gain for a long period of time.

[0006]

To achieve this object, a gain control circuit of the present invention determines a reference signal generator for generating a reference signal for gain control, and an output timing of the reference signal. Timing pulse generator, a mixing circuit for inserting the reference signal into the video signal at the above timing, an amplifier whose gain with respect to the output signal can be adjusted, a circuit for driving the cathode of the CRT by its output, and its circuit output. A detector for detecting the reference signal at the timing, an integrator for converting the detected signal into a DC signal, or a sample-hold capacitor for sampling and holding the detected signal, and an integrated signal or a sample-and-hold voltage and a reference signal. A comparator for comparing the voltage of the generator, the output of the comparator being fed to the gain control terminal of the amplifier. By back, in which to keep the gain of the video signal constant.

[0007]

According to the present invention, the integrated signal or the sampled and held voltage is compared with the output voltage of the reference voltage generator, and the comparison output is fed back to the amplifier so that the video signal gain becomes constant. Therefore, the gain fluctuation in the mixing circuit, the amplifier, and the circuit for driving the cathode of the CRT is absorbed, so that the gain adjustment man-hour can be reduced and the stable gain supply can be performed for a long period of time.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 is an overall configuration diagram of a gain control circuit according to a first embodiment of the present invention, and FIG. 3 is a waveform of a video signal, a reference signal, and a timing pulse. In FIG. 1, 1 is a signal input unit, 2 is a mixing circuit that mixes an input signal and a reference signal, 3 is an amplifier that adjusts the gain for a video signal, 4 is a circuit that drives the cathode of a CRT, and 10 is a CR
At T, they are sequentially connected. Reference numeral 5 is a timing pulse generator that determines the output timing of the reference signal, 6 is a detector that detects the reference signal at the cathode of the CRT, and 7 is a detector 6
An integrator for DC converting the signal detected by
Reference numeral 8 is a comparator for comparing the signal voltage integrated by the integrator 7 with the voltage of the reference signal generator to adjust the gain of the amplifier 3, 9 is a reference voltage generator for generating a reference signal for gain control, Reference numeral 14 denotes a user gain adjustment volume that allows the gain of the amplifier 3 to be changed by the user. Above 2,
3, 4, 5, 6, 7, 8, and 9 are collectively referred to as a gain control circuit 11 for the CRT 10.

The operation of the circuit configured as described above will be described. First, a video signal as shown in FIG. 3A is input from the signal input unit 1. This video signal is output from the timing pulse generator 5 in the mixing circuit 2.
The output of the reference voltage generator 9 is mixed with the reference signal as shown in FIG. 3C at the timing of the timing pulse as shown in FIG. The gain is adjusted by the amplifier 3 and the circuit 4 that drives the cathode of the CRT. The mixed waveform of the gain-adjusted video signal and the reference signal is as shown in FIG. Here, the reference signal is detected by the detector 6 at the timing of the timing pulse generator 5. Figure 3 (e) detected
The reference signal such as is DC-converted by the integrator 7, and is compared with the output voltage of the reference voltage generator 9 by the comparator 8. By feeding back this comparator output to the gain adjustment terminal of the amplifier 3, the gain is kept constant.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, 1, 2, 3,
4, 5, 6, 8, 9, 10, 11, and 14 are the same as those in FIG. The difference from the configuration of FIG.
This is the point where the sample-hold capacitor 7a is used.
With the circuit configuration as described above, the voltage to be compared becomes a pulse voltage from the integrated DC voltage of the first embodiment to a voltage higher than the DC voltage, so that the comparator is less likely to make a comparison error. There is.

[0011]

As described above, according to the present invention, by using the gain control circuit, the gain control adjustment can be reduced and the stable gain can be supplied for a long period of time.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a gain control circuit according to a first embodiment of the present invention.

FIG. 2 is an overall configuration diagram showing a gain control circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a video signal, a reference signal, and a timing pulse waveform in the gain control circuit according to the embodiment of the present invention.

FIG. 4 is an overall configuration diagram showing a conventional gain control circuit.

[Explanation of symbols]

 1 signal input section 2 mixing circuit 3 amplifier 4 circuit for driving cathode of CRT 5 timing pulse generator 6 detector 7 integrator 7a sample and hold capacitor 8 comparator 9 reference signal generator 10 CRT 11 gain control circuit 14 for user Gain adjustment volume

Claims (2)

[Claims] 1. A reference signal generator that generates a reference signal for gain control, a timing pulse generator that determines the output timing of the reference signal, and a mixing circuit that inserts the reference signal into the video signal at the timing. An amplifier whose gain with respect to the output signal can be adjusted, a circuit for driving the cathode of the CRT with the output, and a detector for detecting a reference signal from the circuit output at the timing.
A video signal is provided by including an integrator for converting the detected signal into DC and a comparator for comparing the integrated signal with the voltage of the reference signal generator, and feeding back the output of the comparator to the gain control terminal of the amplifier. Gain control circuit configured to keep the gain of the constant. 2. A reference signal generator that generates a reference signal for gain control, a timing pulse generator that determines the output timing of the reference signal, and a mixing circuit that inserts the reference signal into the video signal at the timing. An amplifier whose gain with respect to the output signal can be adjusted, a circuit for driving the cathode of the CRT with the output, and a detector for detecting a reference signal from the circuit output at the timing.
A sample and hold capacitor for sampling and holding the detected signal and a comparator for comparing the sampled and held voltage with the voltage of the reference signal generator are provided, and the output of the comparator is fed back to the gain control terminal of the amplifier. Thus, a gain control circuit configured to keep the gain of the video signal constant.