Patent ID: 7170353

Claim:
A balanced amplifier circuit in which a single-ended first unit amplifier and a single-ended second unit amplifier are disposed in parallel and driven substantially with a phase difference of 180 degrees and substantially at identical amplitude, with an output terminal of a semiconductor device in a last stage in the first unit amplifier being a first node, an output terminal of a semiconductor device in a last stage in the second unit amplifier being a second node, and a single output terminal of the amplifier circuit as a whole being a third node; comprising: a −90 degrees phase-shift circuit for shifting phase substantially by −90 degrees which is connected between the first node and the third node; a +90 degrees phase-shift circuit for shifting phase substantially by +90 degrees which is connected between the second node and the third node; a first inductance component and a second inductance component having substantially an identical size which are connected to between the first node and the second node; a bias feed terminal connected to a middle point between the first inductance component and the second inductance component for feeding a DC bias to the semiconductor device in the last stage in the first unit amplifier and to the semiconductor device in the last stage in the second unit amplifier, wherein between the middle point and a ground a series circuit made up of at least a resistance and a capacitance is provided.