JPS58171190A - Receiver for color television - Google Patents

Abstract

PURPOSE:To perform effectively the succeeding digital processing and to reproduce a correct picture, by incorporating a circuit to set up the amplitude of a cromasubcarrier to a fixed value on the basis of a burst signal in an A/D converter. CONSTITUTION:A detecting circuit 15 detects the amplitude of a chrominance signal component or a burst signal in an output from an equalizer 14 and the detected voltage is applied to the equalizer 14 to set up the level of the chrominance signal to a fixed value. The signal set up to the fixed value is converted from analog to digital by an A/D converter 12 and then applied to a video signal processing circuit and a band pass amplifier 5.

Description

DETAILED DESCRIPTION OF THE INVENTION - The present invention relates to a color television receiver that digitizes a composite video signal, processes it, and converts it back into a video signal to reproduce an image.

Recently, with the advancement of ultra-LSI technology, conventional analog processing circuits have been digitized, eliminating the need for adjustments.

Efforts are being made to reduce the number of parts and to realize new functions. A similar phenomenon is progressing for color television receivers, and video signal processing and color signal processing, which were conventionally analog processing, are now being digitized. In the case of color television receivers, by going digital, parts that could not be implemented with linear ICs, or could not be implemented with ICs due to high costs, can be implemented with XC, thereby reducing the number of parts. Therefore, overall costs can be reduced. In addition, since there are no variations in parts, there is no need to make adjustments, and changes over time tend to occur. Since digital memory elements can be used, many advantages can be obtained, such as the ability to realize functions that have not been easily realized in the past.

1 and 2 show block diagrams for conventional analog processing and digital processing of color television receivers. According to Fig. 1, lightning and waves entering from antenna 1 are tuned by tuner 2, and intermediate frequency video amplification circuit (VI
P circuit) 3 amplifies and detects the signal to form a composite video signal. Although ' is not shown in the figure, if the VIF circuit 3 is
Since a GC circuit is added, the amplitude of the composite video signal becomes a constant value.

The composite video signal includes a luminance component and a color signal component, and the luminance component passes through the video signal processing circuit 4.

The color signal component is amplified by a bandpass amplifier (BP) 6. The color signal amplitude is automatically controlled by the color signal amplitude CC circuit 6 in combination with the BPA 5 so that the burst amplitude becomes a constant value, and is called an automatic saturation degree control circuit. The color control circuit 7 receives the output of the BPA 5 and controls the amplitude of the color signal, and the tint control circuit 8 controls its phase. The APC and 700 circuit 9 is a circuit that reproduces a carrier synchronized with the phase of the burst and is called a phase synchronization circuit, and applies the reproduced carrier to a demodulator (DEM circuit) 10 to obtain a color difference signal. The color difference signal is combined with the output of the video signal processing circuit 4 in a matrix circuit 11 to obtain primary color signals R, G, and B, which are applied to a cathode ray tube corner display device. Here, the AGO circuit 6 maintains the amplitude of the color signal, which may change due to ghosting or distortion of the transmission equipment, at a constant value based on the burst, and also serves to maintain the color density at a constant value. This is an essential circuit for color television receivers. FIG. 3 shows this situation using a composite video signal, where A is a normal signal and B is a signal in which the color signal and burst amplitude are reduced due to antenna mismatching.

Figure 2 is a block diagram when digitized, and VIP
The output composite video signal is converted into PGM by the human/D converter 12.
converted into a signal. The signal is processed by a system having a block configuration similar to that shown in FIG. 1 to obtain a PGM primary color signal, which is converted into an analog primary color signal by a D/A converter 13 and applied to a display device. 9 & ha APC circuit, 9b is 700 circuit. Since the functions of the circuits are the same, detailed explanation will be omitted. However, the output of the vCO circuit 9b serves as the sampling clock of the A/D converter 12, and at the same time serves as the clock signal of the Tizotal system.

In this case, the number of A/D bits is usually chosen to be 6 to 8 bits. It is well known that if this value is small, false contours will appear due to quantization noise, which is inconvenient. This also applies to color signals, as shown in Figure 3A.
There is no problem when the color signal is normal as in B, but when it is attenuated as in B, the number of gradation steps of the color signal decreases and a false contour occurs in the color. Since the reduced burst is amplified by the CC circuit, false contours are emphasized, resulting in a screen that is very difficult to see. Strictly speaking, the outline should be visible even with the regular color range, but because of the large number of gradations, it is not visible.

In order to eliminate the above-mentioned drawbacks, the present invention is characterized by providing a circuit for setting the color signal amplitude to a constant value before A/D conversion.Embodiments of the present invention will be described below with reference to the drawings. I will explain. 4 and 5 are embodiments 3, and the same parts as in FIG. 2 are given the same numbers and their explanations are omitted. Equalizer 14
is a circuit that recovers the damaged chroma signal. In FIG. 4, a detection circuit 15 detects the amplitude rJJ of the chroma signal component or the noise signal output from the equalizer 14, and the detected voltage is applied to the equalizer 14 to restore the chroma signal to normal. In the case of FIG. 5, A/D is performed to separate the digital signal into chroma signals, from which the amplitude of the burst is detected by the human CC circuit 6. The output is controlled by the control circuit 16
In addition to controlling the equalizer through the chroma level, the chroma level is kept at a constant value by controlling the first gain of BPA6 in the digital signal. In Figure 4, all processing is done in the analog domain, so the circuit is simple. The circuit in Figure 5 is complicated because it spans the digital domain, but since the detection is done after the A/D, the drift of the A/D converter 12 and differences in efficiency are also controlled, so the performance is high. Excellent in terms of purpose. The blending ratio applied to the equalizer 14 and BPA5 is controlled by so-called tirade AGC, such as IF, M(, C, RF, AC, C), and is normally controlled by the equalizer 14. If it becomes impossible, BPmu5 will work better.

FIG. 6, FIG. 7, and FIG. 8 are specific examples of the equalizer.

In FIG. 6, the video input of the terminal 17 is divided into two parts, one is applied to the tlh adder 18, and the other is sent to the adder 18 by varying the phase within the range of ±18Cf' of the chroma subcarrier by a variable phase shifter 19. Add. In this way, the chroma level can be varied from 0 to twice by the amount of phase shift of the variable phase shifter 19, and since the Y signal does not change much over time, it does not change much.

FIG. 7 shows a method for varying the high-frequency gain of the amplifier 2o, which is usually done by emitter peaking of a transistor amplifier.

In FIG. 9, the video signal at the input terminal 21 is branched into two, a chroma removal circuit 22 removes the chroma signal to take out the luminance signal Y, and a chroma extraction circuit 23 takes out only the chroma signal. Then, the gain of the chroma amplifier 24 is varied by the output of the chroma detection circuit 26 to keep the chroma level at a constant value.

As described above, according to the present invention, as long as the chroma level input to the A/D converter is maintained at a correct value, subsequent digital processing becomes effective and a correct image can be reproduced. moreover,
Digitalization itself can achieve significant rationalization.

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams of a conventional color television receiver, respectively, and FIG. 3 is a block diagram of a conventional color television receiver. B is a waveform diagram for explaining the same receiver, Fig. 4, Fig. 614.
... Equalizer, 12 ... A/D converter, 15 ... Detection circuit, 16 ... Control circuit, 5 ... BP, 6... Human CC circuit, 13... D/A converter. Name of agent: Patent attorney Toshio Nakao and one other person
3 Figure 14 Figure

Claims (1)

[Claims] The composite video signal is A/D converted by a MU/D converter, the obtained PCM data is processed, and the processed signal is D/A converted and added to a video display element to reproduce a PCM image. A color television receiver, wherein the input circuit of the A/D converter is provided with a circuit that sets the amplitude of the chroma subcarrier to a constant value with reference to the burst signal.