KR0136508Y1 - Black level control circuit of television - Google Patents

Abstract

The present invention relates to a black level correction circuit that corrects a change in reproduction characteristics due to variation in screen voltage in color television to reproduce an input signal with original signal characteristics.

The present invention decodes only chroma components from a composite video signal and outputs them as R, G, and B signals, and amplifies R, G, and B signals output from the chroma decoder, respectively, and outputs them to the cathode of the CRT. A constant voltage unit for controlling driving of the R, G, and B amplifiers by setting the G, B amplifiers, and cutoff points, an ABL unit for controlling the R, G, and B outputs of the chroma decoder unit according to the beam amount, and horizontal FBT which boosts the pulse voltage generated during the return period when the sawtooth current is obtained from the drive and supplies the CRT anode voltage and the CRT bias voltage, and detects the screen voltage change in the ABL unit and outputs it to the constant voltage unit. In addition, the screen change is detected using the ABL unit, and then it is applied to the constant voltage unit to change the black level in the dark scene to secure the input signal as the original signal characteristic. It can be reproduced.

Description

Black level correction circuit

Figure 1 (a) is an ideal CRT bias change characteristic diagram.

(b) is an ideal CRT bias change characteristic diagram for the FBT characteristic.

2 is a block diagram of a conventional black level correction circuit.

3 is a CRT bias variation characteristic diagram in FIG.

4 is a block diagram of a black level correction circuit according to the present invention.

5 is a detailed circuit diagram of the detection unit and the constant voltage unit of FIG.

6 is a CRT bias variation characteristic diagram according to the present invention.

* Explanation of symbols for main parts of the drawings

10 chroma chroma unit 20 RGB driving circuit

21: R amplifier 22: G amplifier

23: B amplification section 24: constant voltage section

30: automatic beam limiter 40: detector

R1, R2, R3: resistor Q1: transistor

D1, ZD1: Diode C1: Capacitor

The present invention relates to a black level correction circuit for improving the image quality of color television. More specifically, the black level in a dark scene is corrected by correcting a change in reproduction characteristics due to a change in screen voltage in a color television. The present invention relates to a black level correction circuit capable of reproducing original signal characteristics.

Generally, FIG. 1 (a) is an ideal CRT bias variation characteristic diagram, and FIG. 1 (b) is an ideal CRT bias variation characteristic characteristic for a flyback transformer (FBT) characteristic. According to the beam current amount, the screen voltage and the cathode voltage, the CRT light emitting unit and a cut-off unit in which the CRT does not emit light are formed. At this time, the brightness of the image varies depending on the amount of beam current.

If the beam amount is a low beam, the voltage changes from 12.5V as a dark scene to a high beam as a bright scene.

2 is a block diagram of a conventional black level correction circuit, in which a chroma decoder unit 10 decodes only chroma components from a composite video signal and outputs them as R, G, and B signals, and in the chroma decoder unit 10, respectively. RGB driving circuit 20 for amplifying the output R, G, and B signals and outputting them to the cathode of the CRT, and automatic beam limitation for controlling the R, G, and B outputs of the chroma decoder unit 10 according to the beam amount. Beam Limit) 30 and a FBT that boosts the pulse voltage generated during the retrace period when the sawtooth wave current is obtained from the horizontal drive to supply the CRT anode voltage and the CRT bias voltage.

In this case, the CRT bias voltage is a second grid that controls the electron beam as the screen voltage.

The RGB driving circuit 20 includes R, G, and B amplifiers 21, 22, and 23 that amplify R, G, and B signals output from the chroma decoder unit 10, respectively, and as a fixed bias. The constant voltage unit 24 controls the R, G, and B amplifiers 21, 22, and 23 to set the amplification gain and the cutoff point of the CRT drive.

In FIG. 2 configured as described above, the R, G, and B signals output from the chroma decoder unit 10 are amplified by the respective R, G, and B amplifiers 21, 22, and 23 of the RGB driving circuit 20. The electrons are then emitted by being applied to CRT cathodes (RK, GK, BK).

When the beam current more than allowed by the CRT flows, the ABL unit 30 controls the R, G, and B outputs to limit the beam current by feeding back to the chroma decoder unit 10.

In this case, the change characteristic of the CRT bias is a portion in which the image is degraded due to the screen voltage change as shown in FIG. Here, ⓐ is a state where the black level of the screen is floating, ⓑ is a state where the black level of the screen is locked.

That is, the bias of the CRT drive unit is constant because the screen voltage, which is the CRT bias, is changed according to the beam amount, so that the screen displayed on the actual CRT is reproduced by changing the screen voltage variation from the input signal. This is a chronic problem of picture quality.

This invention aims to solve the above problems, and the purpose of this invention is to stabilize the signal reproduction characteristic change due to the change of screen voltage in color television, thereby preventing the degradation of image reproduction characteristics caused by the change of screen voltage (40 ~ 80V). A black level correction circuit for reproducing an image is provided.

A characteristic of the black level correction circuit according to the present invention for achieving the above object is a chroma decoder unit for decoding only chroma components from a composite video signal and outputting them as R, G, and B signals, and outputting from the chroma decoder unit. An R, G, and B amplifiers for amplifying the R, G, and B signals and outputting them to the cathode of the CRT; a constant voltage unit for controlling driving of the R, G, and B amplifiers by setting cutoff points; Black level correction consisting of an ABL unit that controls the R, G, and B outputs of the chroma decoder unit, and an FBT that supplies the CRT anode voltage and the CRT bias voltage by boosting the pulse voltage generated during the return period when the sawtooth wave current is obtained from the horizontal drive. In the circuit, the constant voltage unit is connected in parallel to the base terminal of the transistor and a transistor having an emitter terminal commonly connected to the R, G, B amplifiers, the collector terminal is grounded It is composed of the resistance, and in that the detection unit for detecting a voltage change on the screen, the ABL part output to the base terminal of the constant voltage portion transistor (Q1) is provided.

Hereinafter, a preferred embodiment of the black level correction circuit according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a block diagram of a black level correction circuit according to the present invention, in which a chroma decoder unit 10 decodes only chroma components from a composite video signal and outputs them as R, G, and B signals, and in the chroma decoder unit 10, respectively. RGB driving circuit 20 which amplifies the output R, G, B signals and outputs them to the cathodes (RK, GK, BK) of the CRT, and outputs the R, G, B outputs of the chroma decoder unit 10 according to the beam amount. Automatic beam limiter 30 for controlling, FBT for boosting the pulse voltage generated during the retrace period when the sawtooth wave current is obtained in the horizontal drive and supplying the CRT anode voltage and the CRT bias voltage, and the screen in the ABL unit 30. The detection unit 40 is configured to detect a voltage change and control the constant voltage unit 24 of the RGB driving circuit 20.

At this time, the configuration of the RGB driving circuit and the R, G, B amplifying unit (21, 22, 23) for amplifying the R, G, B signal output from the chroma decoder unit 10, as shown in FIG. It consists of the constant voltage part 24.

FIG. 5 is a detailed circuit diagram of the detector 40 and the constant voltage unit 24 of FIG.

In this case, the constant voltage unit 24 includes a transistor Q1 having an emitter terminal commonly connected to the R, G, and B amplifiers 21, 22, and 23, and a collector terminal of which is grounded, and a base of the transistor Q1. It consists of resistors R2 and R3 connected in parallel to the stages.

The detector 40 includes a ripple removing capacitor C1 connected to the contacts of the resistors R2 and R3 and the base terminal of the transistor Q1 and a Zener connected to the capacitor C1 to set a control voltage. A resistor R1 connected to the diode ZD1, the zener diode ZD1 to limit and set the zener current, and a discharge voltage of the capacitor C1 connected between the resistor R1 and the ABL unit 30. It is composed of a diode (D1) for blocking.

6 is a CRT bias variation characteristic diagram according to the present invention.

In this configuration, the R, G, and B signals output from the chroma decoder unit 10 are amplified through the respective amplification units 21, 22, and 23 of the RGB driving circuit 20, and then the cathode RK of the CRT. , GK, BK) to emit electrons.

At this time, the ABL unit 30 limits the beam current by controlling the R, G, and B outputs by feeding back to the chroma decoder unit 10 when more than the beam current allowed by the CRT flows.

In the constant voltage section 24, the cutoff points of the R, G, and B amplifiers 21, 22, and 23 are set by the resistors R2R3 connected in parallel. At this time, the R, G, and B amplifiers 21, 22, and 23 operate only when a voltage of at least cutoff is input to the R, G, and B amplifiers 21, 22, and 23.

Accordingly, when a specific beam state is detected by the resistor R1 and the zener diode ZD1 of the detector 40, the voltage is stabilized by the capacitor C1 and then applied to the base of the transistor Q1 to emit an emi of the transistor Q1. By controlling the inter-base current, the cutoff points of the R, G, and B amplifiers 21, 22, and 23 are changed.

This can improve image reproduction characteristics especially in low beams.

In more detail, the ABL unit 30 changes to 12.5V in the low beam (dark scene) and '-' voltage in the high beam (bright scene) according to the beam amount.

At this time, the image reproducing characteristic deterioration occurs due to the increase of the screen voltage in the low beam, the ABL voltage at this time goes up to a high (12.5Max).

At this time, the operating point of the emitter voltage of the transistor Q1 is increased by detecting the voltage by the resistor R1 of the detector 40 and the zener diode ZD1 and applying the voltage to the base of the transistor Q1 of the constant voltage unit 24. .

Therefore, as the driving operation voltages of the R, G, and B amplifiers 21, 22, and 23 rise, the black level operates at a voltage higher than that of the average beam, so that the black level is corrected as shown in FIG. At this time, © in FIG. 6 is a portion where the black level is corrected.

On the other hand, the present invention can control the image reproduction according to the FBT characteristics by providing the voltage detected by the ABL unit to the bright stage, and is also applied to all display devices using FBT at a high pressure without being limited to color television. can do.

As described above, according to the black level correction circuit according to the present invention, the screen change is detected using the ABL part and then applied to the constant voltage part to change the black level in the dark scene to stabilize the input signal with the original signal characteristics. It is effective to reproduce.

Claims (3)

A chroma decoder that decodes only chroma components from a composite video signal and outputs the R, G, and B signals, and R, G, which amplifies the R, G, and B signals output from the chroma decoder, and outputs them to the cathode of the CRT. A constant voltage unit for controlling the driving of the R, G, and B amplifiers by setting a B amplification unit, a cutoff point, an automatic beam limiting unit for controlling the R, G, and B outputs of the chroma decoder unit according to the beam amount, and a horizontal drive In a black level correction circuit comprising a flyback transformer for supplying a CRT anode voltage and a CRT bias voltage by boosting a pulse voltage generated in a return period when obtaining a sawtooth current at A transistor Q1 connected in common to the amplifier and having a collector terminal grounded, and resistors R2 and R3 connected in parallel to the base terminal of the transistor Q1. By detecting a voltage change screen minute beam limiting section black level correction circuit as claimed equipped with a detection section for outputting the constant voltage to the base of the transistor section (Q1). The black level correction circuit according to claim 1, wherein the constant voltage unit determines the cutoff points of the R, G, and B amplification units based on the divided voltages of the resistors R2R3 connected in parallel. 2. The detector of claim 1, wherein the detection unit is connected to and controls the ripple removing capacitor C1 connected to the contacts of the resistors R2 and R3 of the constant voltage unit and the base terminal of the transistor Q1. A Zener diode ZD1 for setting a voltage, a resistor R1 connected to the Zener diode ZD1 to limit and set a zener current, and a capacitor C1 connected between the resistor R1 and the automatic beam limiting unit. A black level correction circuit comprising a diode (D1) for interrupting the discharge voltage of the circuit.