Patent ID: 7336125

Claim:
A power amplifier having a parallel combination of a first amplifier for operating irrespective of an amplitude of an input signal to output a signal corresponding to the amplitude of the input signal, and a second amplifier for operating when the amplitude of the input signal is equal to or larger than a threshold to output a signal corresponding to the level of the amplitude of the input signal above the threshold, power-amplifies a signal inputted through an input terminal by said first and second amplifiers, respectively, and outputs an output signal obtained by combining output signals of said first and second amplifiers through an output terminal, said power amplifier comprising: a 90-degree phase-shift power divider connected to an input side of said first and second amplifiers; and a variable electric length power combiner connected to an output side of said first and second amplifier; wherein the input signal is inputted through said input terminal, a first carrier signal and a second carrier signal which lags the first carrier signal by a phase difference of 90 degrees are inputted to said first and second amplifiers through the 90-degree phase delay power divider part, and amplified by said first and second amplifiers, respectively, and a composite output signal obtained through combination in said variable electric length power combiner is outputted through said output terminal, and said variable electric length power combiner is controlled in correspondence to a carrier frequency band of the first carrier signal so that an electric length of said variable electric length power combiner becomes nearly 90 degrees for a central frequency of the carrier frequency band.