Patent ID: 7515001

Claim:
An AC amplifier, comprising: an amplification circuit; and a bias circuit, wherein the bias circuit generates a bias voltage conformed to an amplitude of an AC signal inputted into the amplification circuit, and the bias voltage controls an operating point of the amplification circuit, wherein the AC signal is inputted into the bias circuit via connecting wiring, and the bias voltage generated by the bias circuit is supplied to the amplification circuit via the connecting wiring, and further wherein the amplification circuit has a first MOS transistor of a p- or n-type and a second MOS transistor of an n- or p-type having drains interconnected, the amplification circuit includes a first feedback resistance connected between the drain and a gate of the second MOS transistor, and a first coupling capacitor connected between a gate of the first MOS transistor and the gate of the second MOS transistor, the gate of the first MOS transistor is connected to the connecting wiring, the gate of the first or second MOS transistor is used as an input terminal for the signal to be amplified, and the interconnected drains of the first MOS transistor and the second MOS transistor are used as an output terminal for the amplified signal.