Variable resistor and gain control circuit and integrated circuit having the variable resistor

摘要

A gain control circuit according to the present invention comprises an amplifier circuit for controlling gain thereof to amplify an input signal (RF in) and a control circuit. The amplifier circuit includes an input terminal (T3) for inputting the signal, a first transistor (11) having a drain electrode connected to a first potential through a first resistive means (13) and a source electrode connected to a second potential, and an output terminal (T5 ) connected to a first electrode whereby the amplifier circuit varies the value of a resistance between the source and drain of the first transistor (11) based on the signal supplied to the input terminal (T3). The control circuit is composed of a second transistor (12) having a source electrode connected to the source of the first transistor (11), a drain electrode connected to the drain of the first transistor and a gate electrode supplied with a control signal (Vagc), the control circuit varying the value of a resistance therebetween based on the control signal supplied to the gate electrode. Thus, since the gain control circuit is simple in structure, it can be activated at a low voltage and can realise a wide gain control range. It is also possible to achieve a gain control circuit whose output (RF out) does not have distortion.