Patent ID: 8212618

Claim:
A variable gain amplifier which includes a plurality of individual amplifiers and variably controls a gain by switching to and using one of the individual amplifiers, comprising: an individual amplifier which amplifies a signal input from an input terminal of the variable gain amplifier by an active element, and outputs the input signal; an attenuator which attenuates the input signal by a passive circuit, and outputs the input signal as an attenuated signal; and a virtual ground point providing circuit, wherein said virtual ground point providing circuit includes an isolation active circuit interposed between an input terminal of said virtual ground point providing circuit and a ground node of the variable gain amplifier, and provides, by the isolation active circuit, a virtual ground potential to the passive circuit of said attenuator that is connected to the input terminal of said virtual ground point providing circuit, and wherein the isolation active circuit includes one of a field effect transistor biased to a saturation region and a bipolar transistor biased to a saturation region.