Patent ID: 8614601

Claim:
A power amplifier comprising: an RF signal input terminal; a first amplifier; a second amplifier; a first output matching circuit; a second output matching circuit; and an RF signal output terminal; wherein the first amplifier includes a first transistor with a large element size to exhibit high power added efficiency in a high power state and a second transistor with a smaller element size than the element size of the first transistor to exhibit high power added efficiency in a low power state; an input terminal of the first amplifier and an input terminal of the second amplifier are commonly connected to the RF signal input terminal, and an RF input signal that is supplied to the RF signal input terminal is amplified by the first amplifier and the second amplifier; an output terminal of the first amplifier is connected to an input terminal of the first output matching circuit, and an output terminal of the second amplifier is connected to an input terminal of the second output matching circuit; an output terminal of the second output matching circuit is connected to the input terminal of the first output matching circuit and an output terminal of the first output matching circuit is connected to the RF signal output terminal; an inductive reactance is connected between the output terminal of the second output matching circuit and the input terminal of the second output matching circuit, and a capacitive reactance is connected between the input terminal of the second output matching circuit and a ground voltage; if the power amplifier executes power amplification in the high power state, the RF input signal is amplified by the first amplifier, and a first RF amplified output signal of the first amplifier is output to the RF signal output terminal through the first output matching circuit; the RF input signal is amplified by the second amplifier if the power amplifier executes power amplification in the low power state and a second RF amplified output signal of the second amplifier is output to the RF signal output terminal through the second output matching circuit and the first output matching circuit; the inductive reactance and the capacitive reactance of the second output matching circuit are set at respective predetermined values if the power amplifier executes the power amplification in the low power state and the RF input signal having a first frequency is amplified by the second amplifier; and at least one reactance of the inductive reactance and the capacitive reactance of the second output matching circuit is set at a larger value than the predetermined value if the power amplifier executes the power amplification in the low power state and the RF input signal having a second frequency that is lower than the first frequency is amplified by the second amplifier.