JPS6387894A - Signal switching circuit - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention applies to a display processing circuit of a television receiver or the like.
The present invention relates to an RGB processing circuit using an A conversion circuit.

2. Description of the Related Art Conventionally, display processing methods for signals other than television signals, such as teletext images, personal computer images, word processor images, etc., involve performing analog processing on RGB signals and displaying them on a CRT display device. was.

In recent years, digital technology has been used to perform these processes, converting the RGB signals to A/D, performing various processing on the digital signals, then D/A conversion, and displaying the data on a CRT display device. ing.

However, these display devices are required to be capable of displaying television signals, RGB input signals, and superimposition at the same time. A conventional example in FIG. 4 shows an example of realizing this.

In FIG. 4, 11 is an A/D converter that performs analog/digital conversion of the video signal, 2' is an A/D converter that converts the YS code to switch between an RGB signal and a video signal, and 3
'~5' are converters that A/D convert RGB signals, and d is A/D converter.
D A signal demodulation circuit that demodulates the video signal into Y, U, and V; 1 is a circuit that doubles the speed of the video signal; 8'
are conversion circuits that perform double speed conversion of RGB signals, 9' to 11'
12/ to 15/ are RGB, Y
D/A converter for S signal, 1σ is Y which has returned to double speed converted analog signal.

The circuit 17' that converts the U and V signals into RGB signals is a switching circuit that switches between the RGB signal and the video signal in accordance with the YS signal converted to analog, and superimpose processing 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 video signal flow and the RGB signal flow are completely separate, resulting in a simple configuration. As is clearer, the double speed conversion circuit section and the D/A conversion section are each required separately, which is wasteful in terms of circuit configuration. However, in this configuration, for the RGB system, there is no frequency band restriction in any circuit block except for the band restriction by the sampling rate of the N converters, so the input RGB signals can be faithfully reproduced. It is possible to reproduce it.

The present invention was made in view of the above-mentioned problems, and eliminates unnecessary circuit configurations, and requires high image quality (particularly frequency characteristics) and reproducibility of screen fineness, etc., especially in RGB input. The purpose of the present invention is to provide a signal switching circuit which prevents the characteristics from being degraded when such inputs are received.

Means for Solving the Problems The signal switching circuit of the present invention has a plurality of first input signals, a plurality of second input signals generated by converting the first input signals, and a first input signal. and a switching circuit that switches between the input signal and the second input signal, and a plurality of A/Ds that converts the switched plurality of first signals or the plurality of second signals from analog to digital.
A converter and a plurality of D/A converters that convert a plurality of digitally converted third signals from digital to analog.
converter, and a plurality of control circuits that switch a plurality of reference currents that control output amplitudes of the plurality of D/A converters.

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

Embodiment To achieve the above object, a signal switching circuit according to an example of the present invention utilizes the characteristics of a D/A conversion circuit. Utilizing this feature eliminates image deterioration of RGB signals that require fineness of image.

This feature means that the D/A converter 22 as shown in FIG.
The output of is the power supply V. This can be obtained by changing the current flowing from C to the load resistor 21 connected to the output terminal. The output is, of course, the digital signal of the input. -D3 (explained here using 4-bit D/A), but the D/A converter uses a reference current to determine the current value that flows in response to each bit change. need to be supplied. Here, when the amount of this reference current is changed, the slope of the analog output versus the digital input value changes as shown in the graph shown in FIG. Direct aA in Figure 2
Line B is when the reference current is small, Line B is when the reference current is increased, Line C is when the reference current is increased even more, etc. Even with the same digital input value, the current value flowing through the load resistor 1 is shown. Since the value changes, the value of the output can be changed.

An embodiment of the present invention will be described below.

FIG. 1 shows an overall block diagram of a signal switching circuit in one embodiment of the present invention. In FIG. 1, 1 is an A/D converter for video signals, 2 is an A/D converter for YS that switches between RGB signals and video signals, and 3 to 5 are RGB signals or Y, U, V(7)A/
D Conversion! , 6 is a signal demodulation circuit for demodulating the A/D converted video signal into Y, U, and V; 7 is a processing circuit for superimposing RGB signals on the video signal;
8 is RGB signal or Y.

A switching circuit for switching between U and V signals, 9 a double speed conversion circuit for converting the switched signal to double speed, 10 to 12 D/A converters for D/A converting the signal, and 13 to 15 D/A converters.
16 is a reference current control circuit that switches the reference current flowing through the /A converters 10 to 12;
U, V matrix circuit, 17ba, Y, U, V signal or R
18 is a circuit for converting Y, U, V signals into RGB signals, RGB input signals, and Y, U
, a switching circuit that switches RGB signals converted from V,
Reference numeral 19 indicates a signal that controls whether the signal to be displayed is processed by Y, U, V processing or by RGB signals. 20 is a CRT display device.

As for the signal flow, the video input signal is A/Ded and then converted into pYl, Ul, Vl by the signal processing circuit 6. U, , V, O ratio is 1:
It is not 1:1, but an appropriate ratio is selected. Therefore,
The RGB input signals to be superimposed are Y
, U, V matrix circuit 16, the previous Yl, Ul, V
is converted to a ratio that matches the ratio of , and the subsequent A
/D U3 level that effectively uses the Guinamino Cleanse of converters 3 to 5. U3. Matrixed into U3.

Y/ , U/ , which have been superimposed
The V/ signal is subjected to double speed conversion and sent to U4. U4. U4, and the analog signal U6.
It is converted into U6°U5 and input to the RGB conversion circuit 18. At this time, the reference current of the D/A converters 10 to 12 mentioned above is U4. U4. The reference current control circuit uses a value determined from the relationship between the ratio of U4 and the load resistance of each D/A converter selected to match the ratio of inputs Y, U, and V of the subsequent RGB conversion circuit. It is being streamed by 13.14.15. In this way, the superimposed R
The levels of the G and B signals are matched with the input video signal.

On the other hand, RGB that does not require superimposition processing
・Signals can be processed as Y, U, and V signals in the same way as the processing described above. However, the problem is Y.

Deterioration of frequency characteristics when converting to Y, U, V in the U, V matrix circuit 16, crosstalk between RGB colors, limitation of frequency band in the final stage RGB conversion circuit 18,
There are problems such as errors in the level of each color during conversion, and the input R
GB signals are not necessarily displayed on a one-to-one level. Especially RGs with a large number of displayed characters, small coloring units, etc.
This becomes disadvantageous for displaying B. Therefore, regarding RGB signals, signals that are not subjected to Y, U, and V conversion are inputted to A/D conversion circuits 3 to 5 by a switching circuit 17 controlled by a control signal 19.

The control signal 19 at this time is a signal whose state changes depending on whether the suit is imposed or not.

Switched R1. G"1.B1 is input to the A/D converters 3 to 6. The ratio of these R1, G1.B1 is basically the same as the input RGB ratio of 1:1:1,
The aforementioned U3. U3. A/D conversion is performed with a value different from the ratio of U3. Similarly, the load resistance of the subsequent D/A is selected to match the above-mentioned ratio of T, Y, U, and V, and if the output is an RGB signal, it is processed by the RGB conversion circuit 18. is not performed and is output to the display device 2° by the switching circuit.

In this way, for RGB signals, signal deterioration does not occur in any part other than band limitation by A/D, but the difference in load resistance in D/A and in A/D The difference in the ratios of Y, U, and V causes a difference in the amplitude of the output. Therefore, in this circuit, the reference current control circuits 13 to 1
R5.6 is provided, and the reference current value of each D/A converter 10 to 12 is switched by the control signal 19, thereby absorbing the level difference. G5. A signal B5 can be generated and supplied to the CRT display device 20.

Effects of the Invention As described above, according to the present invention, a reference current control circuit for the D/A converter is provided and the reference current of the D/A converter is switched according to the purpose, thereby making it possible to create a highly accurate RGB image. Obtainable.

[Brief explanation of the drawing]

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 the input-to-output relationship depending on the reference current of the D/A converter, and FIG. A block diagram of the D/A converter, and FIG. 4 is a block diagram of a conventional signal switching circuit. 1 to 6 A/D converter, 6 Signal demodulation circuit, 7 Superimpose processing circuit, 8 Switching circuit, 9 ......Double speed conversion circuit, 1o to 12...D/A converter, 13 to 1
6...Reference current control circuit, 16...Y
, U, ■Matrix circuit, 17...-switching circuit, 18...RGB conversion circuit/switching circuit, 19.
...Control signal, 2o...CRT
Display device. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 23 - Reference current control circuit Figure 3

Claims (1)

[Claims] A plurality of first input signals, a plurality of second input signals generated by converting the first input signals, and a first input signal and a second input signal.
a switching circuit that switches input signals, a plurality of A/D converters that convert the plurality of switched first signals or the plurality of second signals from analog to digital, and a plurality of digitally converted third signals; A plurality of D/A converters that convert signals from digital to analog, and a plurality of control circuits that switch a plurality of reference currents that control output amplitudes of the plurality of D/A converters. Signal switching circuit.