KR910006309Y1 - Gamma characteristic correction circuit - Google Patents

Abstract

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Description

Gamma Characteristic Correction Circuit of Video Camera

1 is a conventional circuit diagram.

2 is a conventional gamma correction curve.

3 is a block diagram of the present invention.

4 is a circuit diagram of the present invention.

(A) is a gamma correction curve of the present invention, (b) is a voltage change between emitters at the base according to the temperature change of the transistor, and (c) is a cut-in voltage change according to the temperature change of the diode. Degree.

* Explanation of symbols for main parts of the drawings

5 gamma correction circuit 10 temperature compensation unit

15: buffer Q1-Q6: transistor

D1-D4: Diode VR1: Variable Resistor

R1-R11: resistance

The present invention always compensates for the inconsistency of the photoelectric conversion characteristics between the imaging device (imaging tube, solid-state imaging device) and the light emitting device (CRT) in the video camera, that is, the gamma characteristic and the change in the gamma correction amount due to the temperature conversion of the surrounding environment It relates to a gamma characteristic compensation circuit of a video camera capable of reproducing a correct image.

Conventionally, in order to correct the gamma characteristic, as shown in FIG. 1, a plurality of series elements composed of diodes D1-D4, resistors R0-R4, and voltage sources E1-E4 are connected in parallel to each other. Similarly, we use the method of obtaining the desired nonlinear resistance characteristics and have the compensation characteristics according to the wiring approximation.

Therefore, when used in a video camera, the curve of FIG. 2 is made to have an exponential curve by using a squared integer to correct a photoelectric conversion mismatch, that is, a gamma characteristic, between a photographing device and a light emitting device (CRT).

However, in the related art, since the gamma point is set as the voltage source (E1-E4) and a plurality of resistors (R0-R4) are configured in parallel in order to obtain a gamma correction curve (nonlinear resistance characteristic), the bias voltage is not constant. It is difficult to obtain the desired characteristic curve due to the change of the point, and when the temperature changes according to the surrounding environment, the current flowing through the diodes (D1-D4) changes according to the temperature, and thus the gamma correction by changing the cut-in voltage. Since the curve is so severe that it is difficult to correctly perform the desired gamma correction, and since only the diodes D1-D4 are formed, it is difficult to perform a predetermined gamma correction for the small signal current.

In view of the above, the present invention is composed of a transistor and a resistor to apply a bias of the transistor to a constant voltage so that a gamma correction can be made with a constant gamma point, and the saturation voltage between the transistor's base emitters Accurate gamma correction can be achieved for small signal currents by using less than the cut-in voltage and similar variations in temperature between transistors and diodes to prevent bias voltages from changing with ambient temperature. This is to compensate for the variation of the bias voltage with the temperature change, that is, the gamma correction curve.

This will be described in detail with reference to the accompanying drawings.

3 is a block diagram of the present invention, and includes a gamma correction circuit unit 5 for adjusting a gamma point and a slope by comparing a video signal with a distribution voltage in a transistor Q2-Q5 to which a constant voltage by a constant voltage source is applied. A buffer for adjusting the overall bias of the gamma correction circuit unit 5 and compensating for the bias change due to the temperature change and buffering and amplifying and outputting the gamma corrected video signal in the gamma correction circuit 5. 15).

4 is a circuit diagram of the present invention, in which a video signal is applied to an emitter of a gamma correction transistor Q2-Q5 to which resistors R7-R10 are connected, and a constant voltage configured as transistor Q1 to a collector of transistors Q2-Q5. A constant bias is always applied from the circle, and the base bias of the transistors Q2-Q5 is configured such that the gamma correction circuit part 5 is applied to the bias voltage after the power supply Vcc is voltage-divided at the resistors R1-R5 and the overall bias is It is configured to adjust the gamma point by adjusting the variable resistor VR1 and the diodes D1 and D2 are variable to compensate for the bias voltage change, that is, the change of the gamma point, according to the temperature change of the transistors Q2-Q5. By connecting the resistor VR1 in series, the temperature compensator 10 is configured to compensate for the gamma point change due to the temperature change through the overall bias change.

The gamma corrected video signal of the gamma correction circuit unit 5, in which the gamma point change according to the temperature change is compensated by the temperature compensator 10, is buffered and amplified through the buffer 15 composed of the transistor Q6 and then output. It is made up.

(A) of FIG. 5 is a gamma correction curve of the present invention, and (b) and (c) show the voltage change according to the temperature change of the transistor and the diode.

In order to perform gamma correction in the present invention configured as described above, a video signal is input to the gamma correction circuit unit 5 composed of transistors Q1-Q5 and resistors R1-R5 (R7-R10).

At this time, the gamma correction circuit unit 5 supplies the collector-side bias voltage of each transistor Q2-Q5 as the bias voltage of the transistor Q1 which is a constant voltage source, and supplies the power supply Vcc to the base of the transistors Q2-Q5. As the voltage divided by -R5) is applied, a bias voltage for setting the gamma point is applied.

That is, an example of the transistor Q2 is as follows. The voltage VA determined by distributing the power supply Vcc to the resistors R1-R5 is applied to the base of the transistor Q2, and the voltage VA ′ due to the video input is applied to the emitter of the transistor Q2. Since the constant voltage is applied from the transistor Q1, which is a constant voltage source, the transistor Q2 is turned on when the voltage VA is greater than the voltage VA ', thereby turning on the transistor Q2. By flowing through R7, the output voltage eo of the gamma correction circuit section 5 has a slope determined by the resistor R7.

The operation of the transistor Q2 is the same in the transistors Q3-Q5.

At this time, if the voltage VA 'due to the video signal is smaller than the voltage VA, the transistor Q2 is' turned on' so that the slope determined by the resistor R7 has the output voltage eo as described above. When the voltage by is greater than the voltage VA and smaller than the voltage VB, the transistor Q3 is 'turned on' so that the slope of the output voltage eo due to the video signal in this range is determined by the resistor R8. .

In this way, one of the transistors Q2-Q5 is 'turned on' according to the size of the video signal, and accordingly, the slope of the output voltage eo is determined by one of the resistors R7-R10. It is applied to (5) to be corrected by the correction curve as shown in (a) of FIG.

Here, the slope of the gamma correction curve is determined by the resistors R7-R10, but the resistors R1-R5 determine the gamma correction point by determining the divided voltages VA, VB, VC, and VD. In addition, the variable resistor VR1 of the temperature compensator 10 adjusts the overall bias voltage to finally generate a desired correction curve as a correction volume for determining a gamma correction point as desired so that correct image reproduction can be performed.

However, depending on where the video camera is used, the change in the ambient temperature becomes extreme, and the bias of the transistors Q2-Q5 holding each gamma point is changed by the change of the ambient temperature, and the bias of the transistors Q2-Q5 is changed. This makes it difficult to reproduce the correct image.

That is, when the change in ambient temperature occurs, the bias change occurs in the constant voltage source composed of transistor Q1, which suppresses the change of the gamma point caused by the temperature change, but it is very slight and almost does not compensate for the change in temperature. Therefore, circuit elements for temperature compensation are necessary.

Therefore, thermistor is used for the temperature compensation, but it is expensive and the temperature change is not similar to that of the transistor, so satisfactory results cannot be obtained. A similar diode is used to compensate for bias voltage changes with ambient temperature.

In FIG. 5, (b) and (c) are shown in FIG.

In other words, as the ambient temperature rises, the base-emitter voltage of the transistor drops as shown in (b) of FIG. 5, so that the gamma correction curve is inclined as shown in (a) of FIG. At this time, since the cut-in voltage is decreased by the characteristic curve as shown in (c) of FIG. 5 according to the temperature, the overall bias voltage is dropped by the diodes D1 and D2 of the temperature compensator 10. The gamma correction curve shifted upward compensates for the correct gamma correction curve at all times.

The gamma-corrected video signal is output through the transistor Q6 of the buffer 15 so that a correct image reproduction can always be obtained, thereby improving the reliability of the video camera.

As described above, the present invention connects a series element of a transistor and a resistor in parallel and applies a bias to the base and the collector of the transistor using a constant voltage so that a constant gamma point can be obtained, and the bias of the transistor that determines the gamma point is determined. The series connection between the variable resistor for control flow and the diode for compensation of the bias change with temperature is configured in series with the biased resistor of the transistor which determines the gamma point. It is possible to perform gamma correction even when the gamma correction curve is changed according to the temperature change so that the correct image reproduction is always obtained so that the reliability of the video camera can be maximized and the quality can be improved. .

Claims (3)

In the transistors Q2-Q5 to which the constant voltage is applied by the constant voltage source, a gamma circuit part 5 for adjusting the gamma point and the slope is adjusted and the overall bias of the gamma correction circuit part 5 is adjusted. And a buffer 15 for buffering and amplifying and outputting the video signal corrected by the gamma correction circuit 5 to compensate for the bias change due to the temperature change. Gamma characteristic compensation circuit of camera. The method of claim 1, wherein the gamma correction circuitry 5 is connected so that the video signal is applied to the emitters of the transistors Q2-Q5 through the resistors R7-R10, and a resistor (at the base of the transistors Q2-Q5). A gamma characteristic correction circuit of a video camera configured to be connected such that a divided voltage of R1-R5 is applied and an output of the transistor Q1, which is a constant voltage source, is applied to a collector of the transistors Q2-Q5. The temperature compensator 10 includes a variable resistor VR1 for adjusting the bias of the gamma correction circuit 5 and a diode D1 (D2) for compensating a bias voltage change according to a temperature change. Gamma characteristic compensation circuit of the video camera connected and configured.