JPS6048954B2 - Color saturation control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color saturation control device for a color television receiver.

Color amplitude control in color television receivers.

Regarding this, there are automatic saturation control devices (usually called ACC circuits) that detect the burst amplitude and maintain a constant color saturation regardless of changes in the surrounding environment, and manual volume control that maintains a constant color saturation regardless of changes in the surrounding environment. There is a saturation control device that controls the saturation level, and both are connected in series. This is sufficient when receiving normal television signals, but in the case of radio waves from public listening systems in remote areas, television signals are often subject to considerable distortion due to the state of equipment maintenance. Condemnation PG and DP characteristics may become extremely poor. When the DG characteristics deteriorate and only the burst signal amplitude becomes extremely small, the ACC circuit maintains a constant amplitude, so the amplitude of the chroma component becomes relatively large and the color saturation becomes extremely high. At this time, if the color saturation is adjusted using a variable resistor, it is possible to obtain the optimum saturation, but the variable resistor must be adjusted each time the channel is turned, which is very inconvenient. The present invention provides a color saturation control device that suppresses the saturation to a constant value so that the saturation does not increase excessively.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a chroma input a enters a gain control amplifier 1, and an output whose gain is controlled according to the voltage of a burst amplitude detection circuit 2 and whose burst amplitude is constant is obtained. The saturation control circuit 3 controls the chroma amplitude using a color saturation control variable resistor 4. However, with the first gate pulse, the amplitude control does not work only during the pulse period, and there is a burst gate circuit that extracts the burst, and only the burst is applied to the burst amplitude detection circuit 2 and the APC circuit 5.
Note that even if the burst is not extracted, this output is sent to the burst amplitude detection circuit 2 or the APC circuit 5 so that it has a constant amplitude.
May be added to. At this time, it is necessary to gate each circuit by applying the first gate pulse b to those circuits as well. The chroma signal c from which the burst has been extracted is applied to a demodulation circuit 6 and reproduced into a color difference signal f. Further, the chroma signal c is amplified in an amplification and gate circuit 7,
Then, among the outputs of this amplification and gate circuit 7, a signal exceeding a certain level is detected by a detection circuit 8, converted into a direct current, and applied to the voltage of a color saturation control variable resistor 4. Superimposed. A feature of the present invention is the use of the second gate pulse d, which will be explained using a specific circuit example. First, in Figure 2, the conventionally used J
The saturation control circuit will be explained. Chroma input a is applied to the base of transistor Q through capacitor C, resistor R, and capacitor C. The chroma component (3.
The amplified signal current flows to the collector of the transistor Q. A direct current is flowing through the transistor Q2. Transistors Q, , Q2 have the same bias, and if R1=R2, the DC current is the same in both. Transistors Q3 to Q are a double-balanced gain control circuit, and color saturation control variable resistors R,. According to transistor Q. , Q, and controls the base voltage of transistor Q.
and Q. , Q, and Q. Transistor Q by changing the collector current distribution. , changing the chroma amplitude appearing at the collector of Q6. That is, the higher the tap voltage of the variable resistors R and O, the larger the chroma component appearing at the collector of the transistor Q6. The chroma component appearing in the collector of will be smaller. Transistors Q, , Q8 turn ON when the gate pulse is applied, and no chroma component (burst) appears at the collector of transistor Q6. Conversely, a burst appears at the collector of transistor σ. Third
The figure is a waveform diagram to explain this, and A is the chroma input a.
corresponds to

B corresponds to the first gate pulse b, which is used for burst sampling and is usually made from a synchronization signal. C corresponds to the chroma signal c after extracting the burst, and is the terminal waveform of the A terminal in FIG. Although the burst is removed from this, whiskers are generated at positions corresponding to the leading and trailing edges of the first gate pulse b. This mustache is transistor Q7,
Q8's 0N, 0FF and the transistor (~Q.'s 0N
, 0FF, and is thought to occur due to the speed relationship of 0FF, and it is unavoidable that it usually occurs at a voltage of about 0.5 to IV. Due to the gain of the demodulation circuit 6, the amplitude of the whisker is often higher than that of the chroma component, and in this case, if peak detection is performed, a detection voltage is generated by the whisker, making it impossible to control the saturation level. In the present invention, the whiskers are arranged in a second shape corresponding to FIG. 3D.
It is gated by a gate pulse d and is sufficiently amplified as shown in FIG. 3E so as not to interfere with peak detection. Figure 4 shows a concrete example of the circuit, in which the chroma signal a passes through the capacitor C3, and the transistors Q, , Q
, 2.

Transistors Q, 3 to Q, 6 are gate circuits driven by the second gate pulse d, and remove gate period signals. Transistor Q. ,Q,O are constant current sources, R,,=2R,
2, so that the collector DC currents of transistors Q9 and Q, O are equal. The output is transistor Ql
6 and is applied through a capacitor C5 to the base of a transistor Q, , a diode D, and a resistor R. O,R. , and when the chroma component exceeds the VBE of transistor Q, 7, transistor Q, , is turned ON and the collector voltage of transistor Ql7 is lowered. The collector voltage is converted to DC by capacitor C4, and the voltage is applied to the terminal of FIG. 2 to reduce saturation. This is negative feedback and is controlled until the transistor Q,, becomes 0FF. The waveform at the collector of transistor Q, , corresponds to Fig. 3E,
Since the level of the chroma signal is sufficiently higher than the level of the whiskers, the transistors Q, , will not be turned on by the whiskers. At this time, the second gate pulse d needs to be sufficiently wider than the first gate pulse b, so the first gate pulse b
If it is created by a pulse obtained by differentiating the trailing edge of the synchronization signal, then
A horizontal pulse may be used to create the second gate pulse d.

As described above, according to the present invention, although the color saturation level does not rise to an extreme level and can be kept at a constant value, the saturation level cannot be controlled due to the whiskers that occur due to the use of the first gate pulse. The shortcomings can also be overcome.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the main part of the conventional example, Fig. 3 is a waveform diagram at various places, and Fig. 4 is a specific circuit diagram of the main part of the present invention. be. 1... Gain control amplifier, 2... Burst amplitude detection circuit, 3... Saturation control circuit, 4... Color saturation control variable resistor, 6... Demodulation circuit, 7... Amplification and Gate circuit 8...detection circuit, a...chroma input,
b...first gate pulse, c...chroma signal from which the burst has been extracted, d...second gate pulse.

Claims (1)

[Claims] 1. A color saturation control circuit that controls the output amplitude of the chroma signal amplification circuit, which has a control circuit that maintains the burst signal amplitude at a constant value, and a color saturation control circuit that stops operation only during the burst period and maintains the maximum amplitude or A burst gate circuit whose amplitude is set to zero, a demodulation circuit which is supplied with the output of the burst gate circuit, and a demodulation circuit which amplifies the output of the burst gate circuit and which outputs both the leading edge and the trailing edge of the gate pulse used in the burst gate circuit. a sampling circuit that extracts the output with a gate pulse having a pulse width that includes the time, detects a signal exceeding a certain level among the outputs of the sampling circuit, and converts this detection signal into a DC voltage; A color saturation control device characterized in that the color saturation control circuit is controlled by this DC voltage.