AGC circuit

摘要

A linear automatic gain control circuit which can be entirely fabricated in an integrated circuit. A voltage divider has a fixed leg and a variable leg connected in series across a signal input. A non-inverting operational amplifier connected between the voltage divider and an output terminal. The variable leg is comprised of a MOSFET transistor having its source connected to the fixed leg. The junction of the source and the fixed leg carries a d.c. voltage applied from the input. A fixed operating voltage is applied to the drain of the transistor which is equal to the d.c. voltage. Signal peaks from the output of the operational amplifier are detected which are in the same polarity sense as the operating voltage. The signal peaks are stored in a storage means having a predetermined time constant. The stored signal peaks are applied to the gate of the transistor, whereby the transistor is enabled to conduct an input signal in the voltage divider symmetrically in both positive and negative directions. No external capacitor is required.