JPS6058637B2 - Automatic saturation control circuit - Google Patents

Description

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

One of the functions added to color television receivers is an automatic saturation control circuit.

This is because the signal may be disturbed in the transmission system, etc., and the color signal may be reproduced larger than necessary. Examples of this circuit are shown in FIGS. 1 and 2. To briefly explain the block diagram in FIG. It enters the color signal amplification circuit 3. The gain of the second stage amplifier circuit 3 is selected to a desired degree of saturation through saturation control using a generally known saturation control variable resistor 4.

The output signal of the first stage amplifier circuit 2 is fed back to the gain control circuit 5 via the capacitor C.

This circuit 5 detects the amplitude of the output signal, holds it for a certain time through a transistor that switches when it exceeds a certain level, and controls the gain of the first stage amplifier circuit 2 using the detected voltage. The block diagram in FIG. 2 shows a similar system, but with a more complex feedback loop. That is, the color signal output of the first stage amplifier circuit 2 is peak-detected by a peak detection circuit 6 made of a diode or the like, the output is further differentiated by a differentiation circuit 7, and this differentiated signal is applied to the gain control circuit 5. This system can be used when various color signal patterns are broadcast.
Although this is good in terms of controlling the saturation level at a constant level, it is a rather complicated circuit. Furthermore, it is difficult to determine the superiority or inferiority of these circuits depending on the viewer's preferences. The present invention takes into account ease of design and provides an automatic saturation control device that can be integrated.

An embodiment of the present invention will be described below based on the drawings. Third
In the figure, the color signal input from the input terminal passes through the color signal amplification circuit 2 and the color signal amplification burst blanking circuit 8.
is input. Here, the burst signal is extracted from the color signal, and the color signal that does not include the burst signal is transferred to the transistor Q.
supplied to the base of The emitter of transistor Q is a resistor connected outside the IC and is an emitter follower.
It is becoming. Capacitor Cl is for detection, capacitor C
2 is for coupling and differentiation, and resistor Ra) R4 is for bias, creating an impedance for differentiation together with resistor 2. At this time, the peak-detected signal is input into the integrated circuit via a capacitor C2 from a terminal different from the terminal for externally connecting the resistor R1, and is applied to the base of the transistor Q2. transistor Q
2 is for switching, and becomes conductive when a large signal enters the base. The load resistor connected to the collector of the transistor Q2 is composed of R5 and a saturation control variable resistor R6, and has a high resistance. Further, the capacitor C3 is for holding the output voltage. Further, the collector of the transistor Q2 is connected to the gain control terminal of the color signal amplification circuit 1. 9 indicates a portion to be incorporated into 1C.

Note that this color signal amplification circuit 1 is configured such that the gain decreases when the voltage decreases. According to the present invention,
It has the advantage that integration is easy and the saturation control section can be easily and freely designed.

It is also possible to prevent oversaturation even if the amplitude relationship between the burst signal and the color signal is abnormal (if the burst signal is input with a smaller amplitude than the color signal, the ACC circuit in the previous stage (As the color signal tries to maintain a constant amplitude, the color signal becomes oversaturated.) Also, the control characteristics can be determined using external resistors and capacitors, which makes the design easy and allows external Fewer parts required.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional automatic saturation control circuit, and Figure 2 is a block diagram of a conventional automatic saturation control circuit.
The figure is a block diagram of another conventional device, and FIG. 3 is a circuit diagram of a main part showing an embodiment of the present invention. 2... Color signal amplification circuit, 5... Gain control circuit, 6... Zeke detection circuit, 8... Color signal amplification burst blanking circuit, 9... Part incorporated in IC, R1... 4C Emitter resistor externally connected to R6・
... Saturation control variable resistance.

Claims (1)

[Claims] 1. In an automatic saturation control circuit equipped with means for peak-detecting the color signal of a color television receiver, detecting its amplitude, and controlling the gain of the color signal amplification circuit, the means for peak-detecting the color signal is installed at the emitter. It consists of an emitter follower type emitter peak detection circuit in which a resistor is externally connected to the integrated circuit, and the output of this emitter peak detection circuit is input into the integrated circuit from a terminal different from the terminal for externally connecting the emitter resistor. An automatic saturation control circuit configured to input and process a control signal for controlling the gain of the color signal amplification circuit.