Patent ID: 8107899

Claim:
A power supply circuit for supplying a voltage to a power amplifier, comprising: an operational amplifier for amplifying a power level control signal which controls a power level of the power amplifier and controlling in accordance with the power level of the power amplifier, an internal current of the operational amplifier at a time of amplifying the power level control signal; and a power transistor for amplifying an output signal of the operational amplifier, and supplying the power amplifier with a voltage, wherein an internal current control signal which indicates the power level of the power amplifier is inputted to the operational amplifier, and the internal current is controlled in accordance with the inputted internal current control signal, wherein the operational amplifier includes: two transistors for amplifying the power level control signal; and two variable current sources for supplying an internal current to the two transistors, and wherein when the internal current control signal increases in magnitude, the two variable current sources increase the internal current to be supplied to the two transistors, and when the internal current control signal decreases in magnitude, the two variable current sources decrease the internal current to be supplied to the two transistors.