Patent ID: 7417507

Claim:
A bias circuit for power amplification comprising: a first amplifying transistor having a base; a voltage drive bias circuit connected to the base of the first amplifying transistor; a reference voltage input terminal connected to the voltage drive bias circuit and to which a reference voltage is externally supplied, wherein the voltage drive bias circuit includes a first transistor having an emitter and supplying a bias current according to the reference voltage to the base of the first amplifying transitor, first and second resistors, a second transistor having an emitter that is grounded, a base, and a collector that is connected to a point between the emitter of the first transistor and the base of the first amplifying transistor through the first resistor, a third transistor having a base connected to the reference voltage input terminal through the second resistor, supplying a bias current according to the reference voltage to the base of the second transistor, and a third resistor having a first end connected to the reference voltage input terminal, and having a second end connected to the base of the first amplifying transistor; a fourth resistor provided between the base of the first amplifying transistor and a connecting point between the third resistor and the first transistor; a linearizer including a fifth resistor, the fifth resistor having a first end connected between the fourth resistor and the base of the first amplifying transistor, and having a second end connected to a grounding point, wherein when the base voltage applied from the reference voltage input terminal is lower than a threshold voltage at which the first transistor is operable, a first current is supplied from the reference voltage input terminal to the base of the first amplifying transistor through the third resistor, and when the base voltage applied from the reference voltage input terminal is equal to or higher than the threshold voltage, a second current is supplied from the reference voltage input terminal to the base of the first amplifying transistor through the voltage drive circuit in addition to the first current.