US Patent 7696827 Power amplifier system provided with improved protection function

A power amplifier system including a power terminal, a ground terminal, an output terminal, a ripple terminal, a control terminal to which a control signal is supplied from outside, a power amplifier circuit connected between the power terminal and the ground terminal, a negative potential detection circuit connected to the output terminal, and a bias circuit which supplies a bias voltage to the power amplifier circuit, and a bias start-up circuit controlling the startup operation of the bias circuit.