JPS5961378A - Black level correcting circuit - Google Patents

Abstract

PURPOSE:To correct the fluctuation of lightness attended with the manual adjustment of contrast, by detecting an adjusting level of contrast and feeding back the output to a black level output control circuit. CONSTITUTION:A video signal is amplified at a transistor (TR) 1b constituting a buffer amplifier 1 and applied to pedestal clamp circuits 2, 4. The adjusting level of contrast is detected with a TR 10b constituting a contrast adjusting level detecting circuit 10, and the contrast adjusting level detecting signal being this output is fed back to an input of the black level output control circuit 6 via a diode 6e. The predestal clamp circuit 2 is controlled with the output signal of the black level output control circuit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a black level correction circuit, and more particularly to a black level correction circuit that can suppress one black level correction operation to a constant value regardless of the manual contrast adjustment position. It is something.

A black level correction circuit is used in a video circuit of a television receiver to correct the black level of a receiving screen.

In this case, the conventionally commonly used black level correction circuit detects the black level in periods other than the horizontal and vertical blanking periods of the video signal, extracts the black level detection voltage, and adjusts the voltage to the video circuit according to this voltage. ``''ξξDestarck 2 F1 circuit gain control circuit respectively (
F-Yo, when the black level detection voltage changes toward the white side of the video signal, the pedestal clamp circuit corrects the video signal to sink it toward the black side, and also increases the total gain of the gain jli control circuit. The p-contrast is made constant by controlling the p-contrast in the direction of increasing the p-contrast.

However, in the black level correction circuit with the above configuration (
-), the gain control circuit for contrast control is provided after the pedestal clamp circuit in the video circuit, so if you manually adjust the contrast, the relationship between the black level correction amount and the contrast will deviate. Accordingly, there is a problem in that manual adjustment of the black level is required.

Therefore, an object of the present invention has been made to solve the above-mentioned problems, and will be described in detail below using a black level correction circuit according to the present invention with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a black level correction circuit according to the present invention. In the figure, 1 is a buffer amplifier that amplifies the video signal A, and the video signal A is used as a pace input, and the transistor 1b is connected between the power supply +Vcc and the ground via a resistor 1a, and this transformer A series body of a resistor 1e and a capacitor 1d that supplies the output signal of the resistor ib to the pedestal clamp circuit 2, a resistor 1e connected between the connection point of the resistor 1c and the capacitor ed and the ground, and the output signal of the transistor 1b horizontally. - A capacitor 1f which is supplied to the vertical reverse pushing circuit 3. This water/vertical reverse pushing circuit 3 inputs the output signal of the pattern amplifier l as a pace input via a resistor 3a, and also inputs the output signal of the pattern amplifier l as a pace input via resistors 3b and 3c.
Inverted type 1 connected between a source Vcc and ground 1)1
1, and a reverse blanking transistor 3e, which is connected between the collector of the transistor 3d and ground, and is turned on by the reverse sinking pulse B.
The collector output of is used as reverse blanking output.

4 is a pedestal clamp circuit, which includes a clamping transistor 4b connected between the input terminal of the horizontal/vertical reverse blanking circuit 3 and the ground via a resistor/wire a, and a power supply +V c connected to the emitter of the transistor 4b. It is composed of a resistor 4c that supplies the voltage c and a capacitor 4d connected in parallel to the resistor 4a. 5 is a black level detection circuit, which uses the reverse blanking output as a pace input, and has a resistor 5a between the power supply +Vcc and ground.
Transistor 5b for level detection connected via
and a capacitor 5c connected in parallel to the resistor 5a.
It is composed of.

A black level output control circuit 6 controls the clamp level and gain of the pedestal clamp circuit 2 and the gain control circuit 7 connected to the subsequent stage in accordance with the output signal of the black level detection circuit 5. The black level output control circuit 6 includes a transistor 6B which receives the output signal of the black level detection port #55 as a pace input via a resistor 6a, and a resistor 6 connected between the emitter of the transistor 6b and ground.
c, a collector resistor 6d, and a diode 6e that adds an output signal of a contrast adjustment level detection circuit 1o (described later) to a black level detection signal and supplies the result to a transistor 6b. Reference numeral 7 denotes a manual brightness adjustment circuit, which is composed of a variable resistor 7a connected between the power supply +Vcc and ground. Reference numeral 8 denotes a clamp voltage control circuit, which combines the emitter output of the transistor 6b constituting the black level output control circuit 6 and the output signal of the manual brightness adjustment circuit 7 and supplies the resistor 8a to the pedestal clamp circuit 2. , 8b. 9 is a manual contrast f1.17J rectifying circuit,
Transistor 6b constituting the black level output section control circuit 6
A part of the contrast control signal system that is supplied from the collector to the gain control circuit 7 via the resistor 6d is connected to the power supply +Vcc.
When the voltage is divided and applied, it is constituted by a series body of a resistor 9a and a variable resistor 9b. Reference numeral 10 denotes a contrast adjustment level detection circuit, which includes a transistor l whose pace input is a contrast control signal supplied from the manual contrast adjustment circuit 9 to the gain control circuit 7 via a resistor 10a'i.
Ob and the power supply +Vcc through this transistor lob
The collector output of the transistor 10b is supplied to the black level output control circuit 6 as a contrast IAI level detection signal.

In the black level correction circuit configured in this manner, the video signal A supplied from the video signal receiving circuit (not shown) is amplified by the transistor lb constituting the buffer amplifier 1, and then sent to the pedestal clamp circuit 2.4. Each is supplied.

The pedestal clamp circuit 4 is supplied from a gate pulse generation circuit (not shown), and the transistor 4b is turned on when a gate pulse C is generated, thereby controlling the pedestal level of the video signal supplied to the horizontal/vertical reverse blanking circuit 3. be clamped. The pedestal level is clamped, and the video signal is inverted and amplified by the transistor 3d forming the horizontal/vertical inverse blanking circuit 3 and output. In this case, transistor 3d
Since a transistor 3e which is turned on by the reverse blanking signal B is provided between the collector output terminal and the ground, the inversion m of the video signal in the part other than the blanking period is removed. The signal is supplied to the optical level detection circuit 5. The black level detection circuit 5 detects the black level included in the output of the horizontal/horizontal blanking circuit 3. i Output @. Therefore, the reverse blanking circuit 3, the pedestal clamp circuit 4, and the black level detection circuit 5 constitute a black level detection section that detects the black level in periods other than the horizontal and vertical iα blanking periods of video No. 43. become. The black level signal outputted from the black level counting circuit 5 is amplified by the transistor 6b constituting the black level output control circuit 6, and then manually controlled by the emitter output voltage control circuit 8. After being combined with the output of the blankness adjustment circuit 7, it is supplied to the pedestal clamp circuit 2 as the clamp fltlJ signal, and the black level of the video signal is corrected. In addition, the collector output of the transistor 6b is combined with the output signal of the variable resistor 9b in the manual contrast adjustment circuit 9, and then supplied as a contrast conversion 1 control signal to the gain control circuit 7 to vary the gain. In this way, contrast control of the video signal is performed. In this case, the gain control circuit 7 for contrast adjustment is located on the rear side of the pedestal clamp circuit 2 provided for black level adjustment.If the contrast is manually adjusted, the black level will fluctuate. become. Furthermore, in this circuit, the transistor 10b constituting the contrast adjustment level detection circuit 10 has a contrast of 'C': -117.
j The P level is detected and the contrast adjustment level detection signal is fed back to the input signal 1 of the black level output control circuit 6 (7 via the reheating diode 6e. As a result,
Fluctuations in brightness due to manual contrast adjustment are corrected, and the corrected output signal from the black level output control circuit 6 controls the pedestal clamp circuit 2 to control the brightness. .

Figure 2 shows the reference level of each color signal with respect to the pedestal level, and Figure 3 shows the contrast relationship between the black level and the blackest level of the video signal. , as shown by the dotted line A, the black level signal fluctuates greatly as the blackest level of the video signal changes, whereas when using the circuit shown in Figure 1, the curve B in Figure 3 As shown in Fig. 3, the black level correction value can be kept almost constant in the range where the maximum black level of the video coefficient varies by approximately 15% with IREt. can be easily changed as shown by curve C.

As explained above, according to the black level correction circuit according to the present invention, even when a gain control circuit for contrast control is provided at the downstream side of a pedestal clamp circuit for brightness control, the system can be easily configured. However, it has an excellent effect of making the black level correction amount constant in relation to the contrast adjustment.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a black level correction circuit according to the present invention, FIG. 2 is a diagram showing the relationship between the pedestal level and each color signal level, and FIG. 3 is a diagram showing the relationship between the pedestal level and each color signal level. The circuit shown in FIG. 1 and the conventional method 1. It is a special) 1415 diagram showing the relationship of R1 road. 1...Buffer Anne 7', 2.4...Pedescle clamp circuit, 3...Horizontal/vertical reverse blanking circuit,
5... Black level detection circuit, 6... Black level output control circuit, 7... Manual brightness adjustment N path, 8... Clamp voltage fi;lJ control circuit, 9... Manual contrast adjustment Circuit 10: contrast adjustment level detection circuit. Patent applicant Nippon Electric Co., Ltd., Representative Director Yozo Sasaki) Figure 2 40 30 "1. IRE 0 0

Claims (1)

[Claims] (1) A black level detection section that detects the black level of the video signal during horizontal and vertical blanking periods, and a black level detection section that is provided in the video signal system according to the black level detection signal supplied from this black level detection section. a black shield output control circuit that performs gain control for a clamp level of a pedestal clamp circuit for level adjustment and a gain control circuit for contrast adjustment provided at a subsequent stage of the pedestal clamp circuit;
and a manual contrast adjustment circuit that varies gain control for the gain control circuit by the black level output control circuit, wherein the black level output control circuit detects the output level of the manual contrast adjustment circuit and controls the black level output. A black level correction circuit characterized in that a contrast adjustment level detection circuit is provided on the input side of the circuit.