JPS6439109A - Automatic gain controlling/amplifying circuit - Google Patents

Abstract

PURPOSE:To keep a fixed output level even when the attack time and the recovery time are accelerated and the signal duty ratio is changed, by taking out the control signal for the main body of an automatic gain control circuit after the peak detection and the detection of the average value. CONSTITUTION:The output of an automatic gain control circuit main body (AGC amplifier) 1 undergoes the envelope detection through a peak detecting circuit 2 and then the detection of the average value through an average value detecting circuit 3 for detection of the signal level. In this case, the circuit detects only the envelope and the recovery time of the circuit 2 can be accelerated up to the amplifying time or so since the ripple component put on the peak detection output can be deleted by the circuit 3. Thus it is possible to accelerate both the recovery time and the amplifying time, to eliminate the fluctuation of the AGC output level caused by the fluctuation of the signal duty ratio and to reduce the distortion of the output signal. Then such an amplifier 1 can be used effectively as an AGC circuit of a system like an IC for a magnetic disk, etc., where the signal duty ratio changes.