JPH0720254B2 - RGB processing circuit - Google Patents

Description

The present invention relates to a D / A for a display processing circuit such as a television receiver.
The present invention relates to an RGB processing circuit that uses a conversion circuit.

2. Description of the Related Art Conventionally, display processing methods for signals other than television signals, such as images of character multiplex broadcasting, images of personal computers, images of word processors, etc., perform analog processing of RGB signals and display them on a CRT display device. Was there.

In recent years, using digital technology for these processes, RGB signals are A / D converted, various processes are performed on the digital signals, and then D / A conversion is performed to display on a CRT display device. ing.

However, most of these display devices are required to be capable of displaying a television signal as well as an RGB input signal and at the same time capable of superimposing. The realization of this is shown in the conventional example of FIG.

In FIG. 4, 1'is an A / D converter for analog / digital conversion of a video signal, 2'is a converter for A / D a YS signal which switches between an RGB signal and a video signal, and 3'-5 '. RGB
A / D converter for the signal, 6 ′ for converting the A / D video signal to Y,
A signal demodulation circuit for demodulating into U and V, a circuit 7'for double speed conversion of a video signal, a conversion circuit 8'for double speed conversion of an RGB signal, and 9'-11 'for digital / converting a double speed converted video signal D / A converter for analog conversion, 12 'to 15' are RGB, Y
D / A converter for S signal, 16 'is a circuit for converting Y, U, V signals returned to double-speed converted analog signal to RGB signal, 17'
Is a switching circuit that switches between an RGB signal and a video signal in accordance with the YS signal after being converted into analog, and the superimposing process is performed here. 18 'indicates a CRT display device.

Problems to be Solved by the Invention In the conventional example configured as described above, the flow of the video signal and the flow of the RGB system are completely different from each other and have a simple structure. Like, with the double speed conversion circuit section
D / A converters are required separately, and in terms of circuit configuration,
It is in vain. However, in this configuration, with regard to the RGB system, the frequency band is not limited in any circuit block except the band limitation due to the sampling rate of the A / D converter, so the input RGB signal is faithfully reproduced. It is possible to

The present invention has been made in view of the above problems, and eliminates the waste of the circuit configuration, and particularly in RGB input, image quality (especially frequency characteristics), that is, reproducibility such as screen fineness is required. It is intended to provide a signal switching circuit which does not deteriorate its characteristics when inputting.

Means for Solving the Problems A signal switching circuit according to the present invention includes a plurality of first input signals, a plurality of second input signals produced by converting the first input signals, and a first input signal. And a second input signal, a switching circuit, a plurality of switched first signals, or a plurality of A / D converters for analog-digital converting the plurality of second signals, and a plurality of digitally converted signals. A plurality of D / A converters for digital-analog converting the third signal,
A plurality of control circuits for switching a plurality of reference currents for controlling output amplitudes of the plurality of D / A converters are provided.

According to the present invention, a plurality of control circuits for switching a plurality of reference currents for controlling the output amplitude of the D / A converter are provided, and
By switching the reference current of the A converter according to the input signal, a highly accurate RGB image can be obtained.

Embodiments In order to achieve the above object, the signal switching circuit of an example of the present invention utilizes the characteristics of the D / A conversion circuit. By utilizing this feature, deterioration of the image of the RGB signal, which requires fineness of the image, is eliminated. This feature is obtained by changing the output of the D / A converter 22 by the current flowing from the power source V _CC to the load resistor 21 connected to the output terminal, as shown in FIG. The output is, of course, the input digital signal D ₀ ~
It changes according to D ₃ (4 bit D / A is explained here), but supplies the reference current to the D / A converter to determine the current value that flows corresponding to each bit change. Need to Here, if the amount of the reference current is changed, the slopes of the analog output and the digital input value change as shown in the graph of FIG. The straight line A in FIG. 2 is when the reference current is small, and the straight line B is when the reference current is increased.
C is when the reference current is increased more than that,
Even with the same digital input value, the value of the current flowing through the load resistor 21 changes, so the output value can be changed.

An embodiment of the present invention will be described below.

FIG. 1 is an overall block diagram of a signal switching circuit in an embodiment of the present invention. In FIG. 1, 1 is an A / D converter of a video signal, 2 is an A / D converter of YS which switches between an RGB signal and a video signal, and 3 to 5 are RGB signals or Y, U, which have converted RGB. V A / D converter, 6 is a signal demodulation circuit that demodulates the A / D converted video signal into Y, U, V, and 7 is a video signal R
Processing circuit for superimposing GB signal, 8
Switching circuit for switching RGB signal or Y, U, V signal, 9 is a double speed conversion circuit for double speed conversion of the switched signal, 10 to 12
Is a D / A converter for D / A converting the signal, 13-15 is a reference current control circuit for switching the reference current flowing to the D / A converters 10-12,
16 is a Y, U, V matrix circuit that converts RGB signals into Y, U, V to facilitate superimpose processing, 17
Is a circuit for switching between Y, U, V signals or RGB signals, 18 is Y, U, V
Circuit to convert the signal to RGB signal and RGB input signal, Y, U, V
A switching circuit for switching the RGB signal converted from the signal 19 indicates a signal for controlling whether the signal to be displayed is processed by Y, U, V processing or is processed by the RGB signal.
20 is a CRT display device.

As the signal flow, the video input signal is A / D-converted and then converted into Y ₁ , U ₁ , and V ₁ by the signal processing circuit 6. At this time, the ratio of Y ₁ , U ₁ , and V ₁ is 1 The ratio is not: 1: 1, but an appropriate ratio is selected. Therefore, it should be superimposed
The RGB input signal is the Y, U, V matrix circuit 16
Converted to a ratio that matches the ratio of Y ₁ , U ₁ , and V ₁ , and
The dynamic range of the A / D converters 3 to 5 in the subsequent stage is matrixed into Y ₃ , U ₃ , and V ₃ at the levels that effectively use them.

The signals of Y ', U', and V'which have been subjected to the superimposing processing are double-speed converted into Y ₄ , U ₄ , and V ₄ , and the D / A converters 10 to 12
Are converted into analog signals Y ₅ , U ₅ , and V ₅ and input to the RGB conversion circuit 18. At this time, the D / A converter 10 mentioned earlier
12 of the reference current is Y _4, U _4, the ratio of V ₄ and, downstream of the input Y of the RGB conversion circuit, U, the load resistance of each of the D / A converter chosen to as to conform to the ratio of V The value determined from the relationship with is fed by the reference current control circuits 13, 14, 15. In this way, the superimposed RGB signal is level-matched with the input video signal.

On the other hand, RGB signals that do not require superimposing processing can be processed with Y, U, and V signals as in the above processing. However, as a problem, in Y, U, V matrix circuit 16
There are problems such as deterioration of frequency characteristics when converting to Y, U, V, crosstalk of each RGB color, limitation of frequency band in RGB conversion circuit 18 at the final stage, level error of each color at the time of conversion, etc.
Input RGB signals are not always displayed at a level of 1: 1. In particular, it is disadvantageous for RGB display such as a large number of displayed characters and a small coloring unit. Therefore, for the RGB signal, the signal that does not undergo Y, U, V conversion is the control signal 1
Input to the A / D conversion circuits 3 to 5 by the switching circuit 17 controlled by 9.

The control signal 19 at this time is a signal whose state changes depending on whether it is superimposing or not. The switched R ₁ , G ₁ , and B ₁ are input to the A / D converters 3 to 5. The ratio of these R ₁ , G ₁ , and B ₁ is basically the ratio of the input RGB.
It is 1: 1: 1 itself, and A / D conversion is performed with a value different from the ratio of Y ₃ , U ₃ , and V ₃ described above. Similarly, the load resistance of the D / A in the latter stage is selected so as to match the ratio of Y, U, and V as described above, and if the output is an RGB signal, the RGB conversion circuit 18
The input signal is input to the display device 20 by the switching circuit without being processed.

In this way, for RGB signals, signal degradation does not occur at any part except for band limitation by A / D.
Due to the difference in load resistance in A and the ratio in Y / U / V in A / D, a difference occurs in the output amplitude. Therefore, in this circuit, by providing the reference current control circuits 13 to 15 and switching the reference current values of the respective D / A converters 10 to 12 by the control signal 19 described above, R ₅ and G that absorb the difference in level are provided. ₅ , B ₅
Can be generated and supplied to the CRT display device 20.

As described above, according to the present invention, by providing the reference current control circuit of the D / A converter and switching the reference current of the D / A converter according to the purpose, a highly accurate RGB image can be obtained. Obtainable.

[Brief description of drawings]

FIG. 1 is a block diagram showing a signal switching circuit according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing an input-output relationship due to a difference in reference current of the D / A converter, and FIG. That
FIG. 4 is a block diagram of a D / A converter, and FIG. 4 is a block diagram of a signal switching circuit in a conventional example. 1 to 5 ... A / D converter, 6 ... signal demodulation circuit, 7 ... superimpose processing circuit, 8 ... switching circuit, 9 ...
Double speed conversion circuit, 10 to 12 …… D / A converter, 13 to 15 …… Reference current control circuit, 16 …… Y, U, V matrix circuit, 17 ……
Switching circuit, 18 ... RGB conversion circuit / switching circuit, 19 ... control signal, 20 ... CRT display device.

Claims (1)

[Claims] 1. A conversion circuit for converting an input R, G, B signal into a Y, U, V signal, and a Y, U, V signal or the R, G, B signal output from the conversion circuit. analog·
A / D converter for digital conversion, a superimpose processing circuit for superimposing the Y, U, V signals digitally converted by the A / D converter into a video signal, and a superimpose processing circuit for the superimpose processing circuit. A D / A converter for inputting the output signal or the R, G, B signals converted by the A / D converter to perform digital / analog conversion; and a case where the input signal is the output of the superimpose processing circuit An RGB processing device comprising a control circuit for controlling the output amplitude of the D / A converter depending on the R, G, B signals.