Patent ID: 6816017
Filing Date: 2004-11-09
Classification: H03F

Abstract:
A power amplifier module comprising:a signal amplifying portion including at least a bipolar transistor as an amplifying element and amplifying and outputting an input signal; a bias circuit for providing an idling current to the signal amplifying portion; a protecting circuit constituted such that when a forward base current of the bipolar transistor exceeds a predetermined value, a current having an amount of exceeding the predetermined value flows from the bias circuit to the protecting circuit; a voltage to current conversion circuit for inputting an output control voltage, converting the output control voltage into a current and controlling an output current of a current source; a power supply voltage detecting circuit for detecting a power supply voltage and converting the power supply voltage into a current and outputting the current; and a current control circuit for inputting an output current of the power supply voltage detecting circuit, converting the output current into a voltage and controlling the voltage to current conversion circuit such that when the voltage is larger than a predetermined voltage, the output current of the voltage to current conversion circuit becomes substantially constant with regard to an input of the output control voltage equal to or higher than the voltage, wherein by making the amount of exceeding the predetermined value of the base current flow to the protecting circuit, an output of the signal amplifying portion is restricted to be equal to or smaller than a predetermined value, and wherein the predetermined value of the base current is made variable in accordance with a change in a power supply voltage.