JP3286989B2 - Variable gain control circuit and video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain control circuit and a video camera.

[0002]

2. Description of the Related Art A variable gain amplifier is mounted on, for example, a video camera as a sensitivity switching circuit, and is used for switching a video signal level. The sensitivity switch of the video camera has, for example, three levels of 0 dB, 9 dB, and 18 dB.
This is provided to arbitrarily correct the B in 9 dB steps with reference to B.

FIG. 3 is a configuration diagram showing a main part of a conventional video camera.

The charge accumulated in the CCD image sensor 21 by the incident light is read out as a video signal and supplied to a CDS (correlated double sampling) circuit 22. CDS circuit 2
2 suppresses the noise of the input signal, and
Output to The variable gain amplifier 23 amplifies the input signal to a predetermined level, and outputs the amplified signal to the process circuit 24. The process circuit 24 performs processing such as clamping, automatic gain control, and gamma correction on the input signal, and outputs the processed signal to the matrix circuit 25. The matrix circuit 25 performs a matrix process on the input signal and outputs a luminance signal Y and color difference signals Q and I.

FIG. 4 is a block diagram showing an example of the variable gain amplifier circuit 23.

The video signal supplied from the CDS circuit 22 to the input terminal 31 is input to the operational amplifier 32, amplified and output from the output terminal 33 to the process circuit 24. Here, the gain A of the variable amplifier circuit 23 is determined by the resistance Ri (where i = 1 to n) switched by the changeover switch 34, and is given by A = 1 + Ri / Ra in the illustrated example.

When it is desired to switch the gain (A) of the variable gain amplifier circuit 23 having such a configuration in, for example, multiple stages for each of the three primary color signals, a large number of resistors Ri and a phase compensation capacitor connected in parallel thereto (FIG. (Not shown) must be switched by the changeover switch 34, which has the disadvantage of increasing the circuit scale.

FIG. 5 is a block diagram showing another example of the variable gain amplifying circuit 23, which is employed to avoid the above-mentioned drawbacks.

A video signal supplied from the CDS circuit 22 to an input terminal 41 is input to a voltage-controlled amplifier 42, and a control voltage 4 from a digital / analog (A / D) converter 47 is output.
The signal is amplified to a gain determined by 8 and output from the output terminal 43 to the process circuit 24.

For example, the gain is set in three stages (0 dB, 9 dB,
When switching to 18 dB), the gain control of the voltage controlled amplifier 42 is performed as follows. Each time the switch 44 is pressed, the control circuit 45 sequentially selects one of three different digital values 46 and outputs it to the D / A converter 47.
The D / A converter 47 converts the digital value 46 into an analog value and supplies it as a control voltage 48 to the voltage-controlled amplifier 42. The gain of the voltage controlled amplifier 42 is
5 corresponding to the digital value 46 output from
B, 9 dB or 18 dB. Here, the functions of the control circuit 45 and the D / A converter 47 are realized by a microcomputer mounted on a video camera as a controller, for example.

[0011]

SUMMARY OF THE INVENTION For the reasons described above,
2. Description of the Related Art A variable-gain amplifier circuit using a voltage-controlled amplifier as shown in FIG. However, voltage-controlled amplifiers generally vary greatly in terms of control voltage versus gain characteristics, their non-linearity, their temperature characteristics, and the like. Therefore, fine-grained multi-stage (for example, 1 dB steps) gain control is performed for the three primary colors. It is difficult to do exactly each of the signals,
For example, it is customary to perform coarse gain control such as 0 dB, 9 dB, and 18 dB.

Due to this variation, for example, a three-plate CC
In the D video camera, there is a problem that a difference occurs in the gain of the three primary color signals and the color balance is deteriorated.

Further, in order to correct this variation and obtain an accurate gain for each of the three primary color signals, individual adjustment is required for each voltage-controlled amplifier, and the adjustment cost is significantly increased. There was a problem that.

Accordingly, the present invention proposes a variable gain control circuit and a video camera capable of performing accurate gain control irrespective of variations in characteristics of individual voltage controlled amplifiers.

[0015]

In order to solve the above-mentioned problems, a variable gain control circuit according to the present invention comprises: a reference pulse generating means for generating a reference pulse signal having an arbitrary amplitude; and an optical black during an input signal vertical scanning period. Pulse superimposing means for outputting a superimposed signal obtained by superimposing a reference pulse signal generated by the pulse generating means in a level signal section; and amplifying the superimposed signal output from the pulse superimposing means with a gain based on a gain control signal. Amplifying means for generating the gain control signal based on a comparison result between the amplitude of the reference pulse signal and a reference value in the output signal output from the amplifying means, and setting the gain of the amplifying means to the reference pulse signal It has feedback amplification means for controlling according to the amplitude.
Further, the video camera of the present invention includes an imaging unit that generates a video signal of a captured image, a reference pulse generation unit that generates a reference pulse signal having an arbitrary amplitude, and an optical black level signal section in a vertical scanning period of the video signal. ,
A pulse superimposing means for outputting a superimposed signal obtained by superimposing a reference pulse signal generated by the pulse generating means; an amplifying means for amplifying the superimposed signal output from the pulse superimposing means with a gain based on a gain control signal; Generating the gain control signal based on the comparison result between the amplitude of the reference pulse signal and the reference value in the output signal output from the amplification means,
And a feedback amplifier for controlling the gain of the amplifier in accordance with the amplitude of the reference pulse signal.

[0016]

In FIG. 1 showing an embodiment of the present invention, a pulse generating circuit 3 generates a reference pulse signal. Here, the amplitude of the reference pulse is set to a value (Er / A) obtained by multiplying the reference voltage Er by the reciprocal of the desired gain A. Pulse superposition circuit 2
Superimposes the reference pulse signal supplied from the pulse generation circuit 3 on the input signal supplied from the input terminal 1 and outputs the signal to the variable gain amplifier 4. The variable gain amplifier 4 amplifies the superimposed signal supplied from the pulse superimposition circuit 2 with a gain determined by the control voltage Ec, and outputs the amplified signal to the output terminal 5 as an output signal.

The reference pulse detection circuit 6 detects the amplitude of the reference pulse in the output signal, and outputs the detected amplitude to the feedback amplifier 7 as a sample voltage Es. The feedback amplifier 7 compares the sample voltage Es with the reference voltage Er, outputs an error signal to the variable gain amplifier 4 as a control voltage Ec, and controls the variable gain amplifier 4 to a desired gain A.

[0018]

Next, an embodiment of the gain control circuit according to the present invention will be described in detail with reference to the drawings.

In FIG. 1 showing the configuration of a gain control circuit according to the present invention, an input terminal 1 receives, for example,
One of the three primary color video signals generated by the three-plate CCD video camera is supplied. Therefore, in this case, the gain control circuit shown in FIG. 1 is provided for each of the three primary color signals.

The pulse generation circuit 3 has an amplitude of the reference voltage Er.
Is multiplied by the reciprocal of the desired gain A (Er / A), for example, in synchronization with the optical black level signal of the input signal.

The pulse superimposing circuit 2 superimposes the reference pulse signal supplied from the pulse generating circuit 3 on the optical black level signal of the input signal supplied from the input terminal 1 and outputs it to the variable gain amplifier 4. FIG. 2 shows an example in which a reference pulse is superimposed on a video signal.

The variable gain amplifier 4 converts a superimposed signal from the pulse superimposition circuit 2 on which the reference pulse is superimposed into a control voltage Ec.
, And outputs it to the output terminal 5 and the reference pulse detection circuit 6 as an output signal.

The reference pulse detection circuit 6 samples / holds the amplitude of the reference pulse included in the optical black level signal section in the output signal, and outputs the detected amplitude value of the reference pulse to the feedback amplifier 7 as the sample voltage Es. .

The feedback amplifier 7 compares the sample voltage Es with the reference voltage Er and generates a control voltage Ec for controlling the variable gain amplifier 4 to a desired gain A based on an error voltage obtained as a difference between the two voltages. Are output to the variable gain amplifier 4.

The control voltage Ec supplied from the feedback amplifier 7
The variable gain amplifier 4 whose gain is controlled by the amplifier amplifies the superimposed signal from the pulse superimposition circuit 2 on which the reference pulse is superimposed so that the error voltage of the sample voltage Es with respect to the reference voltage Er becomes zero, and outputs the output signal as an output signal Output to terminal 5. That is, when the input signal is amplified by A times (that is, when the variable gain amplifier 4 is controlled to gain A), the amplitude of the reference pulse superimposed on the input signal may be set to 1 / A of the reference voltage Er. For example, when the input signal is amplified twice (A = 2), the amplitude of the reference pulse may be set to half the reference voltage Er.

As a result, the variable gain amplifier 4 is controlled to have a constant gain A irrespective of differences in individual characteristics. For example, in the case of a three-chip CCD video camera, each of the three primary color signals is accurately and accurately controlled. Thus, it is possible to perform fine-grained multi-stage (for example, 1 dB step) gain control. Also, since there is no difference between the gains of the three primary color signals,
There is no deterioration in color balance and no increase in adjustment cost.

Further, since the gain of the voltage control type variable gain amplifier 4 is controlled so that the amplitude of the reference pulse becomes constant on the output side, accurate gain control is possible without saturation of the reference pulse. Become.

Although the present invention has been described with reference to the case where the present invention is applied to a three-plate CCD video camera, it may be applied to video cameras of other types or other signal processing devices.

[0029]

As described above, according to the present invention, the variable gain amplifier is controlled by the amplitude of the reference pulse superimposed on the input signal so as to obtain a desired gain irrespective of differences in individual characteristics. Therefore, there is an effect that accurate and fine gain control can be performed.

Further, since there is no gain difference between a plurality of channels, there is an effect that the adjustment cost can be remarkably reduced.

Further, since the gain is controlled so that the amplitude of the reference pulse becomes constant on the output side, there is an effect that signal saturation in the voltage controlled variable gain amplifier can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the operation of the embodiment.

FIG. 3 is a configuration diagram of a video camera as an example of an apparatus to which the present invention and a conventional variable gain amplifier circuit are applied.

FIG. 4 is a block diagram showing an example of a conventional variable gain amplifier circuit 23.

FIG. 5 is a block diagram showing another example of the conventional variable gain amplifier circuit 23.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Pulse superposition circuit 3 Pulse generation circuit 4 Variable gain amplifier 5 Output terminal 6 Reference pulse detection circuit 7 Feedback amplifier Ec Control voltage Er Reference voltage Es Sample voltage

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/235-5/243 H04N 5/20 H04N 9/00-9/09 H04N 5/52 H03G 1/00-3 / 34

Claims (2)

(57) [Claims] A reference pulse generating means for generating a reference pulse signal having an arbitrary amplitude; and a superimposed signal obtained by superimposing a reference pulse signal generated by the pulse generating means on an optical black level signal section in a vertical scanning period of an input signal. Pulse superimposing means for outputting; amplifying means for amplifying the superimposed signal output from the pulse superimposing means with a gain based on a gain control signal; and an amplitude of the reference pulse signal in the output signal output from the amplifying means. A variable gain control circuit comprising feedback amplification means for generating the gain control signal based on a result of comparison between the gain control signal and a reference value, and controlling the gain of the amplification means in accordance with the amplitude of the reference pulse signal. 2. An image pickup means for generating a video signal of a photographed image; a reference pulse generation means for generating a reference pulse signal having an arbitrary amplitude; and the pulse generation in an optical black level signal section in a vertical scanning period of the video signal. Pulse superimposing means for outputting a superimposed signal on which a reference pulse signal generated by the means is superimposed; amplifying means for amplifying the superimposed signal output from the pulse superimposing means with a gain based on a gain control signal; Feedback amplification for generating the gain control signal based on a comparison result between the amplitude of the reference pulse signal in the output signal and a reference value, and controlling the gain of the amplifying means according to the amplitude of the reference pulse signal. A video camera comprising means.