JPH0691636B2 - Contrast control device for digital television receiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a D / A after appropriately processing a digital video signal.
The present invention relates to a digital television that converts and outputs as an analog video signal, and particularly, the CRT of the television.
The present invention relates to a contrast control device that controls the contrast of an image on a screen.

<Prior Art> FIG. 3 is a schematic circuit block diagram of a main part of such a digital television receiver. In FIG. 3, reference numeral a is an A / D conversion circuit for A / D (analog-digital) converting the video signal, b is a video signal processing circuit for processing the A / D converted digital video signal, and c is , Output of video signal processing circuit b is D / A (digital-analog)
A D / A conversion circuit for conversion, d is a CRT that displays the D / A converted analog video signal on a CRT screen.

In such a television receiver, the contrast control circuit conventionally controls the analog amount in the analog signal area A, that is, the area after D / A conversion by the D / A conversion circuit c, and controls the contrast. Or the digital signal area D, that is, the A / D conversion circuit a
There is a region between after the conversion and before the D / A conversion by the D / A conversion circuit c, that is, the second method of controlling the contrast by controlling the digital amount inside the video signal processing circuit b. there were.

However, regarding the contrast control circuit of the first method,
There is a drawback in that the processing circuit becomes complicated in order to emphasize the contrast characteristic and to make the linearity of the analog signal faithful. Further, in the contrast control circuit of the second method, a plurality of signal lines are mounted in order to control each digit of the digital signal, resulting in a significant decrease in work efficiency, and in mounting, the control circuit and the controlled circuit are separated from each other. However, there is a drawback in that the plurality of signal lines become long and carry external noise, and that noise easily occurs due to mutual interference between the lines.

<Purpose of the Invention> The present invention has been made in view of the above-mentioned drawbacks of the related art, and it is not a digital signal area before D / A conversion or an analog signal area after D / A conversion. By adjusting the contrast when converting to an analog signal, the drawbacks of the first method are eliminated to simplify the circuit, and the drawbacks of the second method are eliminated to eliminate the influence of external noise and the mutual influence of lines. The object is to avoid interference, improve work efficiency, and perform more faithful contrast control.

<Constitution of the Invention> In order to achieve such an object, the present invention has a D / A conversion circuit for converting a digital video signal having a reference amount adjustment terminal into an analog signal and a control for generating a control signal for contrast adjustment. Circuit, by inputting the control signal for the contrast adjustment to the reference amount adjustment terminal of the D / A conversion circuit to control the conversion characteristics of the D / A conversion circuit, thereby controlling the contrast. ing.

<Examples> Hereinafter, the present invention will be described in detail based on Examples shown in the drawings. FIG. 1 is a circuit block diagram of a contrast control device for a digital television receiver according to this embodiment. In FIG. 1, reference numeral 1 is an n-bit parallel type D / A conversion circuit that converts a digital video signal into an analog video signal and controls an analog output amount.
A control signal for controlling the analog output amount of the D / A conversion circuit 1 is formed, and the control signal is supplied to the D / A conversion circuit 1.
It is a control circuit that outputs to.

The D / A conversion circuit 1 includes a reference amount adjustment terminal 1a to which a contrast control signal from the control circuit 2 is input and digital signal input terminals 1b1, 1b2, ... To which a digital signal from the digital signal area D is applied. 1bn (when collectively referred to as digital signal input terminal 1b). And an analog signal output terminal 1c that outputs an analog signal to the analog signal area A
It has and. The D / A conversion circuit 1 also has n constant current sources 31, 32, 32, whose constant current values are controlled in response to a control signal from the control circuit 2 provided via the reference amount adjusting terminal 1a.
... 3n (generally referred to as constant current source 3) and n switches 41, 42, ... 4n that are opened and closed in response to a digital signal from the digital signal input terminal 1b (generally referred to as A switch 4) and a resistance circuit 5 are provided inside thereof.

The switches 41, 42, ... 4n each have a movable contact S1 and two individual contacts S2, S3. The movable contact S1 of each switch is the constant current source 31, 32 ,. Individually connected to the output side of 3n. Further, one individual contact S2 of each switch is connected to the resistance circuit 5 side, and the other individual contact S3 is connected to the ground side. In this case, the input terminal 1bn at the left end of the digital signal in the drawing corresponds to the least significant digit (LSB) of the digital signal, and the input terminal 1b1 at the right end of the drawing corresponds to the most significant digit (MSB) of the digital signal.

Next, the operation of this embodiment will be described.

The digital signal from the digital signal area D is input to the digital signal input terminal 1b of the D / A conversion circuit 1. Further, the constant current value of the constant current source 3 is controlled by the control signal from the control circuit 2 applied to the reference amount adjustment terminal 1a of the D / A conversion circuit 1. As a result, the output amount of the analog signal output from the analog signal output terminal 1c from the D / A conversion circuit 1 is controlled. That is, when the reference voltage value output from the control circuit 2 as a control signal is r, the digital signal input is D, and the analog signal output is A, the following relationship is established.

A = K · r · D Here, K is a proportional constant. That is, since the analog signal output A as the video signal is taken out in proportion to the reference voltage value r, the larger the reference voltage value r, the larger the amplitude of the analog signal output A, that is, the analog video signal, and the stronger the contrast. . Conversely, if the reference voltage value r becomes smaller,
The amplitude of the analog signal output A, that is, the analog video signal becomes small and the contrast becomes weak. In this way, the contrast control in the D / A conversion circuit 1 by the control signal of the control circuit 2 is obtained. In addition, analog signal output terminal
Resistor R or 2R in series or parallel in resistor circuit 5 to 1c
Are connected as shown, and n switches 41, 42, ...
・ The most significant digit (MSB) of digital signal input that opens and closes 4n
Or the analog quantity is obtained corresponding to the digital quantity of the least significant digit (LSB).

Although the contrast is controlled by changing the constant current value of the constant current source 3 in this embodiment, the contrast control circuit is also realized when the contrast is controlled by changing the voltage value. In that case,
The control circuit 2 is composed of a reference voltage generation circuit, and includes a constant current source 3
Instead of a constant voltage source is configured. Further, in this embodiment, a parallel type D / A generally used in video processing is used.
Although the conversion circuit 1 is used, a contrast control circuit can be obtained in the same manner even with a serial type D / A conversion circuit.

FIG. 2 is a circuit block diagram of another embodiment. It should be noted in this embodiment that a plurality of D / A conversion circuits, three (11, 12, 13) in this embodiment, are provided, and each D / A conversion circuit 1
Reference numerals 1, 12 and 13 mean that the analog signal output amount is controlled by the control signal from one control circuit 2. The other structure is similar to that of the embodiment shown in FIG.

<Advantages of the Invention> Since the present invention is a direct-current control contrast control device having excellent linearity, a contrast control circuit essential for a television receiver can be configured very easily. In addition, the circuit scale can be significantly reduced compared to the conventional case where the contrast is controlled in the analog signal domain or the digital signal domain, and the effect of external noise is eliminated because there is no mounting distance limiting element. It is possible to obtain an excellent effect that a contrast control circuit having excellent linearity can be obtained without interference between the connecting lines.

[Brief description of drawings]

FIG. 1 is a circuit block diagram according to an embodiment of the present invention, and FIG.
FIG. 3 is a circuit block diagram of another embodiment, and FIG. 3 is a schematic circuit block diagram of a digital television. 1 is a D / A conversion circuit, 2 is a control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-169934 (JP, A) JP-A-57-201313 (JP, A) "Practical Electronic Circuit Handbook (2)" Transistor Technical Editor, CQ Publication Sho 51.5.5.15 Issue P232-234

Claims (1)

[Claims] 1. A D / A conversion circuit for converting a digital video signal having a reference amount adjustment terminal into an analog signal, and a control circuit for generating a control signal for contrast adjustment, wherein the control signal for contrast adjustment is provided. A contrast control device for a digital television receiver, characterized in that the contrast is controlled by inputting it to a reference amount adjustment terminal of the D / A conversion circuit to control the conversion characteristic of the D / A conversion circuit. .