JPH0360586A - Television signal receiver - Google Patents

Abstract

PURPOSE:To make picture quality stable by providing a series circuit comprising a coil, a capacitor and a current control variable resistor and applying an AGC voltage obtained from a video detector output of an intermediate frequency signal processing circuit to a tuner via the current control variable resistor. CONSTITUTION:A voltage fed back from an AGC circuit 10 by an input signal strength of a television signal from an antenna is fed to an anode of a diode 13 of a trap section via an inverse amplifier comprising a transistor(TR) 14. A coil 11 and a capacitor 12 form a capacitive coupling trap and it is connected between a tuner output and a filter having a selectivity shown in figure 4. A current control variable resistor is required between the trap and ground, in which the resistance varies with a supplied current, e.g. a PIN diode is used. The current flowing to the PIN diode is changed by the voltage fed back from the AGC circuit and the resistance is changed. The change in the resistance varies the attenuation characteristic of the trap.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television signal receiver, and particularly to an AGC circuit of an intermediate frequency amplification circuit thereof.

BACKGROUND OF THE INVENTION FIG. 2 is a schematic circuit block diagram of an intermediate frequency amplification/detection/amplification circuit applied to a conventional intercarrier type television signal receiver. In FIG. 2, 1 is a TV antenna, 2 is a tuner that extracts the signal of the channel to be received from among the VHF and UHF signals received by the TV antenna, amplifies it, converts it to an intermediate frequency, and outputs it;
3 is a filter having the necessary selectivity characteristics to be applied to the intermediate frequency band; 4 is a video intermediate amplification circuit; 6 is a video detection circuit for extracting a video signal from the video intermediate frequency signal; 6 is a video amplification circuit; and 7 is a video amplifier circuit. Frequency difference between video carrier wave and audio carrier wave Cfp4
s''), that is, an audio detection circuit that extracts an audio intermediate frequency signal; 8, an audio intermediate amplifier circuit that amplifies the audio intermediate frequency signal extracted by the audio detection circuit and performs an amplitude limiting action; 9;
10 is an FM detection circuit which controls the gain of the tuner and the video intermediate amplifier circuit so as to keep the video detection output level constant according to the level of the received television signal.
It is a circuit.

FIG. 3 is a spectrum diagram of the video signal baseband output of the television signal receiver. Here, f, represents the audio carrier, f, the color subcarrier, and f, -f, the beat disturbance caused by interference between the audio carrier f and the color subcarrier f0.

Generally, in a television signal input from an antenna, a beat component fo-f is generated between the color subcarrier f and the audio carrier f due to distortion in the tuner, video intermediate amplification, and video detection circuit. As a countermeasure against this problem, conventionally, the selectivity characteristics of the intermediate frequency input circuit are set so that the level of the audio carrier wave f8 becomes an appropriate value as shown in FIG.

Problems to be Solved by the Invention The television signal input through the antenna is distorted in the tuner, video intermediate frequency amplification circuit, and video detection circuit due to interference between the color subcarrier f0 and the audio carrier f. A beat component is generated. If this beat component level is f,,f
In proportion to the level of , especially in strong electric fields, the fa-fs level changes due to deterioration of the 5GO characteristics and the input electric field characteristics, and the beat component tends to increase. leading to quality deterioration.

Means for Solving the Problems The present invention adds a trap that can vary the degree of attenuation of the audio carrier wave f5 to the hexagonal portion of the intermediate frequency circuit, and provides a 5G signal.

The structure is such that the change is detected and the f8 level is controlled to be lowered when there is a strong electric field, thereby suppressing the beat generation caused by the video intermediate frequency amplification circuit button and the video detection circuit.

The mu GO voltage that is fed back to the R7771 stage of the action tuner is also fed back to a variable attenuation type trap such as a pin diode, and as the electric field input increases, f.

The level of the sound carrier wave f3 is attenuated by increasing the attenuation degree of the trap, thereby reducing the generation of beats.

Example Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

In FIG. 1, due to the input electric field strength of the television signal from the antenna, the voltage fed back from the five GC circuits is connected to the seventh node side of the diode 13 in the trap section via an inverting amplifier consisting of a transistor 14. A capacitively coupled trap is formed by the coil 11 and the capacitor 12, and is connected between the tuner output and a filter having the selectivity shown in FIG. A current-controlled variable resistor whose resistance value changes depending on the applied current is required between this trap and the ground; for example, a pin diode is used. At this time Mu GO
As the voltage fed back from the circuit changes, the current flowing into the pin diode changes and its resistance value changes. By changing this resistance value, the attenuation characteristics of the trap are varied.

Effects of the Invention As described above, according to the present invention, it is possible to vary the level of the audio carrier wave f applied from the tuner output to the video detection circuit to an appropriate level according to the level of the television signal input from the antenna. Furthermore, the f, -f, and beats that occur due to interference between the color subcarrier f0 and the audio carrier f are suppressed, and stable image quality can be maintained.

[Brief explanation of drawings]

FIG. 1 is a schematic circuit block diagram of an intermediate frequency amplification/detection circuit in a television signal receiver according to an embodiment of the present invention, FIG. 2 is a schematic circuit block diagram of a conventional television signal receiver, and FIG. A television signal and beat disturbance spectrum diagram, FIG. 4 is a selectivity characteristic diagram of the filter of FIG. 2. 1...TV antenna, 2...Tuner, 3...Filter, 4...Video intermediate frequency amplification circuit, 6...Video detection Circuit, 6...
...Video amplification circuit, 7.-Song audio detection circuit, 8...
...Audio intermediate frequency amplification circuit, 9...-FM detection circuit, 10...Music GC circuit, 11...
Coil, 12. Mountain: Capacitor, 13. River: tR control variable resistor, 14. Inverting amplifier circuit.

Claims (1)

[Claims] A tuner, an intermediate frequency signal processing circuit, an AGC circuit that controls the gain of the tuner and the intermediate frequency signal, and a coil and a capacitor connected in series between the IF output terminal of the tuner and the intermediate frequency band filter to ground. A television set comprising a series circuit comprising a current-controlled variable resistor, and configured to apply an AGC voltage obtained from a video detection output of an intermediate frequency signal processing circuit to the tuner via the current-controlled variable resistor. signal receiver.