JPS62188582A - Gain control circuit for video frequency amplifier - Google Patents

Abstract

PURPOSE:To constantly obtain the same value in the quantity of change in the gain of all video frequency amplifiers when the gains of the plural video amplifiers are simultaneously changed by amplifying a superimposing signal by the video frequency amplifier, thereafter sampling it, comparing the levels of the sampled signals and controlling the gains of the respective video amplifiers so as to be equal according to the difference. CONSTITUTION:During a horizontal blanking period, the R.G.B signals on which the signal of a fixed level is superimposed are amplified by the video frequency amplifiers 2r, 2g, 2b and only the superimposing signal is sampled by superimposing signal sampling circuits 6r, 6g, 6b. By making the signal superimposed on, for instance, the R signal of the sampled signals a reference, the levels of the G signal and the B signal are compared in signal level comparison circuits 7g, 7b. If there is the difference in the level between the signal superimposed on the R signal and the signal superimposed on said signal, the output voltage of gain control voltage generating circuits 8g, 8b is impressed to gain control voltage terminals 4g, 4b and the gain of the video frequency amplifiers 2g, 2b is changed so as to make the difference in the level of the signal superimposed during the horizontal blanking period zero.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit that controls the gains of a plurality of video amplifiers so that when the gains are changed simultaneously, the amount of change is always equal.

[Conventional technology]

FIG. 2 relates to a conventional video amplification circuit. In this conventional example, in Fig. 0, which describes a case where three video amplifiers are provided for three RGB signals,
lr, Ig, lb are R1G, B signal input terminal, 2r respectively
, 2g, 2b are respectively R1G, B video amplifier, 3r, 3g
, 3b are R1G and B signal output terminals, R1, R2, R
3, R4 is a resistor, and VRl, VH2, and VH2 are variable resistors. Furthermore, 4r, 4g, and 4b are R and G, respectively.

This is a gain control voltage input terminal for the B video amplifiers 2r, 2g, and 2b.

Next, the operation will be explained. R, G, B signal input terminal 1
The R, G, and B signals arriving at r, Ig, and lb are amplified by video amplifiers 2r, 2g, and 2b, respectively, and sent to the respective output terminals 3.
r, 3g, and 3b as output signals. The gains of the video amplifiers 2r, 2g, and 2b can be controlled by changing the DC voltage of the gain control voltage input terminal 4r+4g+4b.

Gain control of the video amplifiers 2r, 2g, and 2b is performed by variable resistors VRI, and gain control voltage input terminals 4r, 4 at the same time.
This is done by changing the DC voltages of g and 4b.

However, the value of the gain control voltage and the amount of change in gain of each video amplifier are not necessarily the same. Therefore, variable resistor VR1
, the variable resistor VR2 is set so that the gain of the R video amplifier 2r and the gains of the other video amplifiers 2g and 2b are the same when a voltage determined by the voltage division ratio of the resistors R1 and R4 is applied to the gain control voltage input terminal 4r. , adjusted by VR3. Note that the resistors R2 and R3 are used to prevent the voltage at the gain control voltage input terminal 4r from changing when the resistance value of the variable resistors VR2 and VR3 (7) is changed.

[Problem that the invention seeks to solve]

Conventional video amplifier gain control circuits are configured as described above, so when the gain is at a certain level, the gains of the three video amplifiers can be made the same using an auxiliary variable resistor, but the gain When changing , there was a problem that the gains of the three video amplifiers did not necessarily change in the same way.

This invention was made to solve the above-mentioned problems, and when the gains of multiple video amplifiers are changed at the same time, it is not possible to always make the amount of gain change of all the video amplifiers the same value. The purpose of this study is to obtain a gain control circuit for a video amplifier that can be used.

[Means for solving problems]

The superimposed signal is amplified by a video amplifier and then extracted, the levels of the extracted signals are compared, and the gain of each video amplifier is controlled to be the same according to the difference.

[Effect]

In this invention, the gain control circuit functions so that the gain of each video amplifier becomes the same according to the level difference of the signals superimposed during the horizontal blanking period, so the gain of each video amplifier always remains the same. be equal.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows a gain control circuit of a video amplifier according to an embodiment of the present invention, and in the figure, tr, tg.

1b are R-G-B signal input terminals, 2r and 2g.

2b is an R-G-B video amplifier, 3r and 3g.

3b is an R-G-B signal output terminal, 4r and 4g.

4b is a gain control voltage input terminal of each of the video amplifiers 2r, 2, g, and 2b. Also, VRI is a variable resistor,
The gain control voltage input terminals 4r, 4g.

By changing the voltage of 4b, the video amplifier 2r
, 2g, and 2b are controlled. R1゜R2, R3
are gain control voltage input terminals 4r and 4g.

This is a resistor inserted so that the voltages of 4b do not affect each other.

Further, 5 is an input terminal for a superimposed signal and a superimposed signal extraction pulse, 6r, 6g, and 6b are superimposed signal extraction circuits, 7g,
7b is a signal level comparison circuit, and 8g.

8b is a gain control voltage generation circuit, R4 and R5 are resistors, 9
r, 9g, and 9b are signal superimposition circuits.

As explained in the conventional example, the same voltage set by the variable resistor VRI is applied to the gain control voltage terminals 4r, 4g, 4b of the video amplifiers 2r, 2g, 2b. 2t) has variations in its gain, so the output signal levels are not necessarily the same. Therefore, the signals superimposed on the R, G, and B video signals during the horizontal blanking period are amplified and extracted, the levels of the extracted signals are compared, and the gains of the video amplifiers 2r, 2g, and 2b are controlled according to the difference. This is the principle of the present invention.

The operation of one embodiment of the present invention will be described below. R
, G, B signal input terminals 1r, Ig, lb, input terminal 5 for superimposed signal and superimposed signal extraction pulse
The superimposed signals from the signal superimposing circuits 9r, 9g, 9b,
Superimposed on the horizontal blanking period of R, G, and B signals. A signal of a certain level is superimposed during this horizontal blanking period.
-c-BH8 is amplified by video amplifiers 2r, 2g, 2b, and superimposed signal extraction circuits 6r, 6g, 6b.
Accordingly, only the superimposed signal superimposed during the horizontal blanking period is extracted. Among these extracted signals, for example, R
Using the signal superimposed on the signal as a reference, the levels of the superimposed signals of the G signal and the B signal are compared by signal level comparison circuits 7g and 7b. If there is a level difference between the signal superimposed on the reference R signal and the signal superimposed on that signal, the output voltage of the gain control voltage generation circuits 8g and 8b will be the output of the signal level comparison circuit 7.7b. The value is the sum of the signal held by the signal and the voltage set by the variable resistor VRI. This gain side? II + voltage generation circuit 8g, 1
The output voltage of 3b is applied to gain control voltage terminals 4g and 4b via resistors R4 and R5. The applied voltage changes the gains of the video amplifiers 2g and 2b so that the level difference between the signals superimposed during the horizontal blanking period becomes zero.

That is, the gain of the video amplifiers 2g and 2b is always the same as that of the video amplifier 2r.
will be the same as the gain of

〔Effect of the invention〕

As described above, according to the gain control circuit for a video amplifier according to the present invention, when performing gain control of a plurality of video amplifiers,
A signal with a constant amplitude is superimposed on the horizontal blanking period of each human-powered video signal, and after amplification, these superimposed signals are extracted, and the difference voltage obtained by comparing the level differences between them is sent to the video amplifier. Since it is configured to provide feedback, it has the advantage that the gains of a plurality of video amplifiers can always be made the same.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a gain control circuit for a video amplifier according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional circuit. In the figure, lr, Ig, and lb are R, G, and B signal input terminals, 2r, 2g, and 2b are R, G, and B video amplifiers, and 3
r, 3g, 3b are R, G, B signal output terminals, 4r, 4g
, 4b is a gain control voltage input terminal, 5 is an input terminal for a superimposed signal and a superimposed signal extraction pulse, 6r, 6g, and 6b are superimposed signal extraction circuits (signal extraction means), and 7g and 7b are signal level comparison circuits (level difference detection 8g and 8b are gain control voltage generation circuits (gain control means), 9r and 9g. 9b is a signal superimposition circuit (signal superposition means), VRI. VR2 and VR3 are variable resistors, R1, R2, R3゜R4
, R5 are resistors. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) In a gain control circuit of a video amplifier that changes the gain of a plurality of video signals simultaneously, a signal superimposition means for superimposing a signal having the same amplitude on a horizontal blanking period of each input video signal; Signal extraction means for extracting the signal superimposed during the horizontal blanking period from the amplified signal by the video amplifier; Level difference detection means for comparing the levels of each of the extracted signals and detecting the difference; and the detected level. gain control means for controlling the gain of each video amplifier according to the difference, and the amount of change is always the same when the gain of each video amplifier is changed simultaneously. circuit.