Patent ID: 7609113

Claim:
A constant current bias circuit, comprising: an output stage operably coupled with a first voltage, for amplifying a radio frequency (RF) signal; and a bias circuit operably coupled with the output stage, wherein the bias circuit comprises: a first bias transistor having a base and a collector, the collector of the first bias transistor operably coupled with a second voltage through a first impedance element; a second bias transistor having a base, a collector, and an emitter, the base of the second bias transistor operably coupled with the collector of the first bias transistor, the collector of the second bias transistor operably coupled with the second voltage, and the emitter of the second bias transistor operably coupled with a ground through a second impedance element; a third bias transistor having a base and a collector, the base of the third bias transistor operably coupled with the base of the first bias transistor and with the emitter of the second bias transistor; and a fourth bias transistor having a base, a collector, and an emitter, the base of the fourth bias transistor operably coupled with the collector of the first bias transistor, the collector of the fourth bias transistor operably coupled with the second voltage through a third impedance element, and the emitter of the fourth bias transistor operably coupled with the collector of the third bias transistor.