Patent ID: 7525387

Claim:
An amplifier circuit, comprising: a first bipolar transistor of which the emitter is grounded; and a bias circuit of the first bipolar transistor, wherein the bias circuit includes a second bipolar transistor constituting a current mirror circuit along with the first bipolar transistor, a first resistor connected to the bases of the first bipolar transistor and the second bipolar transistor, and a third bipolar transistor of which the emitter is connected to the bases of the first bipolar transistor and the second bipolar transistor through the first resistor, and of which the base is connected to the collector of the second bipolar transistor, wherein the first bipolar transistor amplifies a signal input to the base thereof and then outputs the amplified signal from the collector of the first bipolar transistor, and a voltage is applied from a voltage source to the collector of the third bipolar transistor and the bias circuit has a second resistor connected to the collector of the third bipolar transistor.