US Patent 7777571 High frequency power amplifier

A high frequency power amplifier comprises: a multi-finger transistor with transistor cells electrically connected in parallel; an input side matching circuit connected to gate electrodes of the transistor cells; and resonant circuits respectively connected between the gate electrode of a transistor cell and the input side matching circuit. The resonant circuit resonates at a second harmonic of the operating frequency of the transistor or within a predetermined range of frequencies having a center at the second harmonic of the operating frequency, and becomes a high-impedance load at the second harmonic, or an open load.