POWER AMPLIFIER

PURPOSE:To obtain the power amplifier in which a power transmission efficiency between the power amplifier and external circuit is maintained even in the presence of fluctuation of a power supply voltage by controlling the capacitance of a capacitive element of a matching circuit with the power supply voltage in the power amplifier provided with the matching circuit for the external circuit. CONSTITUTION:Since it is unavoidable that an input/output impedance characteristic of an amplifier circuit 3 changes against a change in a power supply voltage, the impedance is matched by varying a component value of matching circuits 1,2 corresponding to the power supply voltage fluctuation. That is, when a power supply voltage is fluctuated resulting in fluctuating an impedance level, the capacitance of capacitive elements 1a, 2a of the matching circuits 1,2 varies with the power supply voltage fluctuation. it is possible to provide the function of impedance conversion between the amplifier circuit 3 and an external circuit for the matching circuits 1,2 to prevent the reduction in the power transmission efficiency. Thus, the characteristic fluctuation against the power supply voltage fluctuation is suppressed to improve the stability of a communication equipment.