AUTOMATIC GAIN ADJUSTMENT CIRCUIT

PROBLEM TO BE SOLVED: To reduce the temperature dependence of an output amplitude of a variable gain circuit.SOLUTION: An automatic gain adjustment circuit includes: a peak detection circuit 10 for detecting a peak voltage of an output signal of a variable gain circuit 3; an average detection/output amplitude setting circuit 11 for detecting an average voltage of the output signal of the variable gain circuit 3, and adding a voltage that is half a desired output amplitude of the variable gain circuit 3 to the average voltage; and a high gain amplifier 12 for amplifying a difference between an output voltage of the peak detection circuit 10 and an output voltage of the average detection/output amplitude setting circuit 11, and controlling the gain of the variable gain circuit 3 with a gain control signal, which is the result of amplification. The number of base-emitter junctions of transistors inserted in a path from an input terminal to an output terminal of the peak detection circuit 10 is the same as the number of base-emitter junctions of transistors inserted in a path from an input terminal to an output terminal of the average detection/output amplitude setting circuit 11.