US Patent 10469032 Power amplifier circuit

A power amplifier circuit includes a transistor, a bias current source, and an adjustment circuit. The transistor amplifies an RF signal when supplied with a variable power supply voltage. The bias current source supplies a bias current to the base of the transistor through a first current path. The adjustment circuit increases a current flowing from the bias current source to an input terminal of a matching circuit through a second current path as the variable power supply voltage decreases, and decreases the bias current flowing from the bias current source to the base of the transistor through the first current path as the current flowing from the bias current source to the input terminal through the second current path increases.