AGC Improvement circuit of response speed in operating AGC of tuner

摘要

The present invention aims to prevent a phenomenon of instantaneous screen collapse or skipping during search due to a slow response speed of the AGC voltage during channel switching and channel search in the tuner AGC speed up circuit.;To this end, the present invention has an output of an IF amplifier 5 that detects and outputs an IF signal of a desired channel from an RF signal received through an antenna, and has an input stage buffer unit including a PNP transistor Q1 and a bias resistor R1-R3. And the AGC voltage output of the input end buffer part 13A is composed of a resistor R4 and capacitors C1 and C2. Is provided to the RF amplifier 1 as an RF AGC control voltage signal, and at both ends of the resistor R4 in the RC filter unit 13B, when the AGC voltage drops, the previous AGC is transferred to the RF amplifier 1. The AGC acceleration circuit unit 15 includes a capacitor C3 for delaying the voltage output and a transistor Q2 for outputting the AGC voltage without delay to the RF amplifier 1 in parallel when the AGC voltage surges. It is characterized by.