MOS-FET AMPLIFIER CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide a MOD-FET amplifier circuit capable of keeping the drain current of the amplifying MOS-FET of an input signal to be optimal so as to be free from change with lapse of time. SOLUTION: This MOS-FET amplifier circuit 200 amplifies an input signal by an amplifying MOS-FET 1 which has an operation point set by a drain current flowing between a source and a drain in the case of no-input. For purpose of this, the circuit 200 has a simulating MOS-FET 2 for simulating the operation of the MOS-FET 1 and a monitoring control circuit 3 which includes a simulating bias circuit where a constant drain current flows without regard to the lapse of time with respect to the MOS-FET 2, detects the gate-source voltage VGS2 of the MOS-FET 2 varied with the lapse of time, and gives gate- source voltage VGS1 for the MOS-FET 1 corresponding to the detected voltage to the gate of the MOS-FET 1 to operate the MOS-FET 1 optimally without change with lapse of time.