Patent ID: 7129786
Filing Date: 2006-10-31
Classification: H03F

Abstract:
1. A bias circuit comprising: a first bias circuit and a second bias circuit connected to a reference voltage source and a power amplifier and providing different currents for the power amplifier; a switching device for selectively dropping down a voltage level of the reference voltage source that is provided to each bias circuit, wherein the first bias circuit and the second bias circuit each includes a first transistor and a second transistor, wherein a base of the first transistor is connected to a collector of the second transistor through a first node, an emitter of the first transistor is connected to a base of the second transistor through a second node, a collector of the first transistor is connected to a power supply source, an emitter of the second transistor is grounded, the first node is connected to the reference voltage, and the second node is connected to the power amplifier in each bias circuit, wherein the switching device includes a first switching transistor and a second switching transistor connected between the first node and the reference voltage source, and a mode change transistor connected between a mode selection voltage source and the second switching transistor, wherein each collector of the switching transistors is connected to the first node of each bias circuit, each emitter of the switching transistors is grounded, a base of the first switching transistor is connected to the mode selection voltage source, a base of the second switching transistor is connected to a collector of the mode change transistor, an emitter of the mode change transistor is grounded, and a collector of the mode change transistor is connected to the reference voltage source.