Patent ID: 6919761

Claim:
A variable gain amplifier having an input terminal and an output terminal, for amplifying a signal inputted to the input terminal to output the amplified signal, operating in a high gain mode or a low gain mode, comprising: an amplifier element having a first terminal constituting the input terminal of the variable gain amplifier, a second terminal constituting the output terminal of the variable gain amplifier and a third terminal connected to a second power supply, wherein the amount and direction of current of the amplifier element, which flows from the second terminal to the third terminal, are varied based on the amount of a voltage applied to the first terminal; a wideband-matching element connected between the input terminal and the output terminal of the variable gain amplifier, for matching input impedance at a wideband upon the operation of the variable gain amplifier in the high gain mode; an attenuator connected between the input terminal and the output terminal of the variable gain amplifier, for attenuating the input signal to output the attenuated signal to the output terminal upon the operation of the variable gain amplifier in the low gain mode; means connected to the first terminal of the amplifier element, for activating the amplifier element upon the operation of the variable gain amplifier in the high gain mode; and a load resistor connected between the second terminal of the amplifier element and a first power supply.