Patent ID: 7477104

Claim:
A power amplifier circuit which outputs an output voltage corresponding to an input voltage supplied thereto, comprising: a positive-side output unit which includes a positive-side output resistor, and a positive-side transistor having its source terminal connected to one end of the positive-side output resistor to make a current corresponding to a voltage supplied to its gate terminal flow to the positive-side output resistor; a negative-side output unit which is connected to the positive-side output unit and includes a negative-side output resistor, and a negative-side transistor having its source terminal connected to one end of the negative-side output resistor to make a current corresponding to a voltage supplied to its gate terminal flow to the negative-side output resistor; a positive-side bias generating unit which generates a positive-side bias voltage corresponding to the input voltage; a negative-side bias generating unit which generates a negative-side bias voltage corresponding to the input voltage; a positive-side control unit which controls the voltage to be applied to the gate terminal of the positive-side transistor in a manner that the positive-side bias voltage and a source voltage of the positive-side transistor become generally equal; a negative-side control unit which controls the voltage to be applied to the gate terminal of the negative-side transistor in a manner that the negative-side bias voltage and a source voltage of the negative-side transistor become generally equal; and a resistance control unit which controls an output impedance of the power amplifier circuit by controlling the resistance values of at least one of the resistors included in the power amplifier circuit, wherein the power amplifier circuit outputs a voltage at a connection node between the positive-side output unit and the negative-side output unit, as the output voltage.