US Patent 7522001 Power amplifier

An emitter follower circuit applies to an input terminal of a second amplifying device a voltage according to a reference voltage applied to a reference terminal. First and second resistors are connected in series between the reference terminal and an input terminal of a first amplifying device. The collector of a first transistor is connected to the reference terminal and a control voltage is applied to the base of the first transistor. A third resistor is connected between the emitter of the first transistor and a grounding point. A current mirror circuit draws a current proportional to a current input from the collector of the first transistor from a connection point of the first and second resistors.