JP2001358971A - Automatic amplitude correction circuit for video input signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic amplitude correction circuit for a video input signal that utilizes a circuit with a simple configuration to automatically correct the amplitude of a video signal outputted from a video image photographing device and can output the video signal with a prescribed amplitude to an image display device. SOLUTION: The automatic amplitude correction circuit for a video input signal consists of a series connection of a capacitor, a clamp circuit and a gain control amplifier connected between a video signal input terminal and a video signal output terminal in this order from the video signal input terminal, of an analog/digital converter that receives a reference level signal outputted from the clamp circuit and converts the signal into a DC, and of a comparator circuit that compares a reference level of the video signal received as a DC signal from the analog/digital converter with a specified reference level to generate an amplitude correction signal and to give it to the gain control amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for automatically correcting the amplitude of a video signal output from a device for photographing or reproducing a video image.

[0002]

2. Description of the Related Art Generally, video signals obtained by a video camera at various shooting sites are displayed as visible images on an image display device (eg, monitor) such as a CRT or a liquid crystal display. Since video image capturing apparatuses and image reproducing apparatuses (eg, video decks) are manufactured industrially under strict process control, individual errors of each product do not pose a problem in general use.

However, in the case where the fidelity of a reproduced image is particularly required, for example, for obtaining a video image used for medical diagnosis, a video signal output from a video image capturing device (video camera) is used. The slight amplitude error (variation) may affect the original image reproduction characteristics of the finally reproduced video image. Also,
Even in a display device such as a CRT, there is often a slight variation in the electrical characteristics. Therefore, the variation in the amplitude of the video signal output from the video photographing device and the variation in the electrical characteristics on the display device side are combined. Therefore, there is a problem that the variation is amplified and the original image reproduction characteristics of the video image displayed on the display device are likely to be insufficient.

[0004]

SUMMARY OF THE INVENTION According to the present invention, a circuit having a simple structure is used to automatically correct the amplitude of a video signal output from a video image photographing apparatus, so that it can be applied to an image display apparatus such as a CRT. An object of the present invention is to provide an automatic amplitude correction circuit for a video input signal capable of outputting a video signal having a constant amplitude.

[0005]

According to the present invention, a capacitor, a clamp circuit for defining a DC reference level are arranged between a video signal input terminal and a video signal output terminal in order from the video signal input side, and A gain control amplifier for adjusting the amplitude of the video input signal is provided in series, and further receives a reference level signal output from the clamp circuit and converts the reference level signal into a direct current.
The reference level of the video signal input as DC from the A / D converter and the A / D converter is compared with a predetermined standard reference level to generate an amplitude correction signal. In the automatic amplitude correction circuit for the video input signal, which is composed of a comparison circuit to be sent.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an automatic amplitude correction circuit for a video input signal according to the present invention will be described with reference to the accompanying drawings.

In FIG. 1, one end has a video signal input portion connected to an output terminal of a video image output device (eg, a video camera or a video deck), and the other end has a CRT.
An example of a video input signal automatic amplitude correction circuit according to the invention in an aspect connected to a display is shown.

In the automatic amplitude correction circuit shown in FIG. 1, a capacitor 14 and a DC reference level are arranged between a video signal input terminal 11 and a video signal output terminal 13 of a CRT display 12 in order from the video signal input side. And a gain control amplifier 16 for adjusting the amplitude of the video input signal are connected in series.

The automatic amplitude correction circuit shown in FIG. 1 further receives an A / D converter 17 for receiving a reference level signal output from the clamp circuit 15 and converting it into a direct current, and is input as a direct current from the A / D converter 17. The comparison circuit 1 compares the reference level of the video signal with a predetermined reference level to generate an amplitude correction signal and sends the signal to the gain control amplifier 16.
8 is attached.

The automatic amplitude correction circuit shown in FIG. 1 amplifies a video signal whose amplitude has been adjusted by a conventional gain control amplifier 16 and outputs the amplified video signal to a video signal output terminal 13.
A preamplifier circuit 19 and a final-stage amplifier 20 are provided.

An automatic amplitude correction circuit according to the present invention connects a conventional video signal input terminal and a conventional video signal output terminal to transmit a video signal from a video camera or a video deck to a CR.
The difference from the circuit to be sent to the display device such as T is that the clamp circuit 15, the A / D converter 17, the comparison circuit 18 and the gain control amplifier 19 are interposed in particular. Alternatively, their functions will be described in detail mainly on the device.

First, a video signal input from a video signal input terminal 11 is AC-coupled in a capacitor 14 and sent to a clamp circuit 15. In the clamp circuit 15, the video signal is clamped at the reference level for a fixed time according to the clamp signal. As a result, the reference level (pedestal level) of the video signal is secured and then sent to the A / D converter 17.

In the A / D converter 17, the reference signal in the video signal sent from the clamp circuit 15 is subjected to analog / digital conversion, and the reference signal converted into a digital signal is then sent to a comparison circuit 18.

In the comparison circuit 18, the A / D converter 17
Is compared with a standard value (standard amplitude level of the reference signal) by using a gate signal separately input from the gate signal input circuit 21. Then, the result of the comparison is sent to the gain control amplifier 16 as a comparison signal (a signal indicating an amplitude correction value).

The gain control amplifier 16 corrects the amplitude of the video signal based on the comparison signal sent from the comparison circuit 18 and indicating the result of comparison between the reference signal and the standard value of the video signal. For this reason, the video signal output from the gain control amplifier 16 becomes a signal having the same amplitude as the standard value, and the error of the amplitude of the video signal caused by the error of various characteristics of the device that supplies the video signal is eliminated. .

The video signal whose amplitude error has been corrected as described above is supplied to a preamplifier circuit 19 and a final amplifier 20 which are also provided in a circuit between the conventional video signal input device and the video image display device. After that, the video signal is output from the video signal output terminal 13 and the video image display device (CRT, etc.)
At 12, a video image having excellent original image reproduction characteristics is displayed.

[0017]

According to the present invention, by incorporating an automatic amplitude correction circuit for a video input signal between a video signal input terminal and a video signal output terminal, errors in various characteristics of a device which supplies a video signal can be reduced. A video signal in which the resulting error in the amplitude of the video signal is reduced can be supplied to the video image display device, and a video image having excellent original image reproduction characteristics can be displayed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a video input signal automatic amplitude correction circuit according to the present invention.

[Explanation of symbols]

 Reference Signs List 11 Video signal input terminal 12 CRT display 13 Video signal output terminal 14 Capacitor 15 Clamp circuit 16 Gain control amplifier 17 A / D converter 18 Comparison circuit 19 Preamplifier circuit 20 Final amplifier 21 Gate signal input circuit

Claims (1)

[Claims] 1. An arrangement from a video signal input side between a video signal input terminal and a video signal output terminal in order:
A capacitor, a clamp circuit that regulates a DC reference level, and a gain control amplifier that adjusts the amplitude of a video input signal are provided in series, and further receive a reference level signal output from the clamp circuit, and An A / D converter for converting to direct current, and comparing a reference level of a video signal input as direct current from the A / D converter with a predetermined standard reference level to generate an amplitude correction signal, An automatic amplitude correction circuit for video input signals consisting of a comparison circuit fed to a gain control amplifier.