Patent ID: 7936219

Claim:
A power amplifier and bias circuit comprising: a first amplifier transistor having an emitter, a base, and a collector; a voltage drive bias circuit connected to said base of said first amplifier transistor; a current drive bias circuit connected in a parallel relationship with said voltage drive bias circuit and connected to said base of said first amplifier transistor; first and second resistances; and an idle current control circuit for controlling bias current input to said base of said first amplifier transistor in accordance with collector voltage of said first amplifier transistor, wherein said voltage drive bias circuit and said current drive bias circuit are connected to a reference voltage input terminal to which a reference voltage is externally applied, said voltage drive bias circuit includes: a first transistor having an emitter, a base, and a collector, supplying a bias current corresponding to the reference voltage to said base of said first amplifier transistor, a second transistor having a collector connected between said emitter of said first transistor and said base of said first amplifier transistor, through said first resistance, having a grounded emitter, and having a base, and a third transistor having a base connected to said reference voltage input terminal, through said second resistance, and supplying a bias current corresponding to the reference voltage to said base of said second transistor; said current drive bias circuit includes a third resistance connected at a first end to said reference voltage input terminal and at a second end to said base of said first amplifier transistor, and said idle current control circuit includes a first control section transistor having a collector connected between said base of said first amplifier transistor and parallel circuitry including said voltage drive bias circuit and said current drive bias circuit, having a base receiving a current corresponding to the collector voltage of said first amplifier transistor, and an emitter.