Patent ID: 8593223

Claim:
An automatic gain control circuit comprising: a peak detection circuit which detects and outputs a peak voltage of an output signal from a variable gain circuit which amplifies a main signal, and includes transistors; an average value detection/output amplitude setting circuit which detects an average value voltage of an output signal from the variable gain circuit, outputs a voltage obtained by adding a voltage with an amplitude ½ a desired output amplitude of the variable gain circuit to the average value voltage, and includes transistors; and an amplification circuit which controls a gain of the variable gain circuit by amplifying a difference between an output voltage of the peak detection circuit and an output voltage of the average value detection/output amplitude setting circuit and outputting the amplification result as a gain control signal to the variable gain circuit, wherein the number of base-emitter junctions of transistors on a path in the peak detection circuit from input ports which receive output signals from the variable gain circuit to an output port which outputs a voltage to the amplification circuit is equal to the number of base-emitter junctions of transistors on a path in the average value detection/output amplitude setting circuit from input ports which receive output signals from the variable gain circuit to an output port which outputs a voltage to the amplification circuit.