JPS6151833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color television receiver (hereinafter referred to as
This paper relates to improvements in the performance of automatic color saturation control (hereinafter referred to as ACC) and color cancellation and automatic phase control (hereinafter referred to as APC), which govern color signal processing in CTV (hereinafter referred to as CTV).

FIG. 1 shows a block diagram of the color signal processing section of a conventional CTV. 1 is an input terminal for the carrier color signal;
The carrier color signal consists of a burst signal 31 and a chroma signal 32, as shown in FIG. 2a. Input terminal 1
The input chrominance signal is amplified by a first chrominance signal amplifier 11 and a second chrominance signal amplifier 12, and a burst signal 3 is amplified by a burst signal-chroma signal separator 13.
1 and a chroma signal 32. chroma signal 3
2 is controlled to have an appropriate amplitude by the color saturation controller 14 and then output to the chroma signal output terminal 2 through the output stage 15. On the other hand, the burst signal 31
are routed to each functional block to perform ACC, color cancellation, and APC operations. Reference numeral 18 denotes a burst signal peak value detector, and the peak value of the burst signal detected here is fed back to the first color signal amplifier 11 after being amplified by the amplifier 17 .
This feedback loop makes the amplitude of the burst signal at the output of the second color signal amplifier 12 constant.
In other words, if the color signal input is sufficiently small that detector 1
In the absence of the output of 8, the amplifier 11 operates at maximum gain, so the output of the amplifier 12 is proportional to the input. When the color signal input becomes large and the detector 18 starts operating, its output is amplified by the amplifier 17 and acts on the amplifier 11 to lower its gain.
As a result, the output of amplifier 12 remains at the amplitude it had when detector 18 began operating. This relationship is illustrated in FIG. 3. Here, the vertical axis 41 indicates the output amplitude of the amplifier 12, and the horizontal axis 44 indicates the amplitude of the burst signal at the input terminal 1.
The input/output relationship is shown by a solid line 42.
However, when used in actual CTV, the input/output relationship will be as shown by the dotted line 43. This is because the peak value detector 18 is used to detect the amplitude of the burst signal. That is, in the case of a burst signal without noise as shown in FIG. 2b, the detector 18 detects _H1 as the amplitude, but in the case of a burst signal containing noise as shown in FIG. 2c, the detector 18 detects H1 as the amplitude. detects H ₂ as the amplitude of the burst signal. In an actual CTV, the signal waveforms shown in FIG. 2b and c correspond to medium, strong, and weak electric fields, respectively. Therefore, when the electric field is weak in actual CTV,
The ACC characteristic is not shown by the solid line 42 in FIG.
Indicated by dotted line 43. This has the effect of preventing dark color noise from appearing on the screen when the electric field is weak, making the screen easier to see.

In addition, the burst signal separated by the separator 13 enters the synchronous detection circuits 19 and 22, and is multiplied by the color subcarrier generated by the voltage controlled oscillator (hereinafter referred to as VCO) 21, thereby increasing the amplitude of the burst signal. Or the phase is detected. The synchronous detection circuit 19 is
The amplitude of the burst signal is detected, and its output is amplified by the amplifier 20. When the amplitude of the burst signal becomes very small, it acts on the color saturation controller 14 to reduce the output level of the chroma signal to 0. west,
Perform color erasing. This is indicated by the solid line 42 or dashed line 43 arrow in FIG. Synchronous detection circuit 22
detects the phase of the burst signal and its output is
Acting on VCO21, the frequency of the burst signal,
Create phase-matched color subcarriers. This color subcarrier is used for demodulating the chroma signal in addition to the above-mentioned synchronous detection of the burst signal. 16 is a demodulator, and 3, 4 and 5 are demodulation output terminals.

What should be noted here is that although both ACC and color cancellation detect the amplitude of the color burst signal, their detection methods are different. In other words, in the ACC part, the burst signal is detected by detecting the peak value, so when there is a lot of noise, such as in a weak electric field, the noise is detected even if the original burst signal is small and ACC does not operate. Therefore, the gain of amplifier 11 is lowered. Therefore, the signal amplitude at the chroma signal output terminal 2 is
The noise is smaller than when there is no noise, and the colors on the CTV screen are fainter, but the color noise is also smaller, making the screen easier to see.

On the other hand, in detecting the amplitude value of a burst signal for color erasure, malfunctions due to noise are a problem, so synchronous detection, which is resistant to noise, is often used. However, in the configuration shown in FIG. 1, as the noise increases, the amplitude of the original burst signal entering the synchronous detector 19 also decreases, resulting in a problem that the color erasing operation becomes faster. It was hot.

In addition, synchronous detection is used to detect the phase of the APC burst signal, but when the electric field is weak, the amplitude of the burst signal similarly decreases quickly, so the output of the synchronous detector 22 becomes small and the APC does not operate. It disappears. Furthermore, if synchronous detection is used for detection in the ACC section, the original characteristics shown by the solid line 42 in FIG. 3 can be obtained, but since color noise is also amplified as it is,
The screen becomes very difficult to view with a lot of color noise.

Therefore, the main purpose of this invention is to make it easier to see images on the screen even when color noise becomes large, to stabilize the operating point of color cancellation, and to
An object of the present invention is to provide a color signal processing circuit for CTV that can sufficiently operate APC.

To summarize, the present invention includes, in a CTV color signal processing circuit, a color signal input terminal, means connected to the input terminal to perform ACC by detecting the peak value of a burst signal containing a noise component, and a means for performing ACC at the input terminal. an amplifier with a constant gain connected to the amplifier; means connected to the amplifier to detect the amplitude of the burst signal and perform color cancellation; and a means connected to the amplifier to detect the phase of the burst signal to perform ACC. It is equipped with means.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. This FIG. 4 is the same as the above-mentioned FIG. 1 except for the following points. That is, the separation circuit 13
Separate the chroma signal and burst signal by
The separated burst signals are applied to the synchronous detectors 19 and 22. In FIG. 4, the burst signals applied to the input terminal 1 are amplified with a constant gain by the amplifier 23, I decided to give it to By providing the amplifier 23, the burst signal is always amplified at a constant rate, and the amplitude or phase is detected by the synchronous detectors 19 and 22, which are resistant to noise. No more APC range reduction. In addition, since ACC uses the same circuit as before,
Even if the color noise becomes large, the gain of the amplifier 11 is suppressed, so the color noise on the screen becomes small and the screen becomes very easy to view.

As described above, according to the present invention, the amplitude or phase of a burst signal is detected to perform color cancellation or APC.
When performing synchronous detection, a burst signal is applied to an amplifier with a certain amplification degree for synchronous detection, so that unlike conventional methods, the burst signal becomes smaller due to noise components and the color erasing operation becomes faster.
APC operating range is not reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional color signal processing circuit, Fig. 2 is a waveform diagram showing a color signal, and Fig. 3 is a block diagram showing a conventional color signal processing circuit.
A diagram showing the input/output characteristics of the color signal processing circuit shown in Fig. 4.
The figure is a block diagram showing one embodiment of the present invention. In the figure, 1 is a color signal input terminal, 2 is a chroma signal output terminal, 11 is a first chroma signal amplifier, 12 is a second chroma signal amplifier, 13 is a burst signal-chroma signal separator, and 14 is a color saturation controller. , 15 is an output stage, 16 is a demodulator, 17 is an amplifier, 18 is a peak value detector, 19 and 22 are synchronous detection circuits, 20 and 23 are amplifiers, and 21 is a voltage controlled oscillator. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A first amplifying means for amplifying a carrier color signal including a color burst signal applied to an input terminal, and a color burst signal from the carrier color signal amplified by the first amplifying means. separation means for separating;
automatic color saturation control means, comprising a peak value detection means for detecting a peak value of the color burst signal separated by the separation means and controlling the amplification degree of the first amplification means; a second amplifying means for amplifying the color burst signal with a constant gain, detecting the amplitude of the color burst signal amplified by the second amplifying means, and if the amplitude value is less than a predetermined value, the automatic color color erasing means for erasing colors by limiting the signal level of the carrier color signal derived from the saturation control means; detecting the phase of the color burst signal amplified by the second amplifying means; A color signal processing circuit for a color television receiver comprising automatic phase control means for controlling an oscillator that produces phase-matched color subcarriers. 2. The color television according to claim 1, wherein the color erasing means and the automatic phase control means include synchronous detection means for detecting the amplitude of the color burst signal by comparing the color burst signal and the color subcarrier. Color signal processing circuit of the receiver.