Electronic circuit with unit for attenuating at least one input signal of an amplifier in an automatic gain control loop

摘要

The electronic circuit (1) includes, in an automatic gain control loop, an input amplifier (2), an AGC unit connected to the amplifier output to detect the amplitude of an output signal and a unit (10) for attenuating an input signal of the amplifier based on an adaptation signal (V_AGC) from the AGC unit. The attenuation unit includes a means of comparing the adaptation signal to a reference signal (V_REF) and for supplying an attenuation current as a function of the difference between the adaptation and reference signals, to a diode-connected PMOS replica transistor (M2), which is connected by a source to a common mode voltage (V_CM) dependent on the input signal of the amplifier. The replica transistor controls a PMOS shunt transistor (M1) defining a shunt resistance connected to the amplifier input, whose resistive value depends on the attenuation current passing through the replica transistor.