Circuit for automatically biasing rf power transistor by use of on-chip

Abstract

A circuit arrangement automatically sets quiescent collector current conditions for a class A/B RF power transistor, which is configured of a plurality of parallel-connected transistors formed in a common semiconductor die. The biasing circuit arrangement includes a temperature-sensing transistor having its collector-emitter current flow path coupled with a programmable constant current source. A differential amplifier circuit is coupled to the base and emitter electrodes of the temperature sensing transistor, and generates a bias voltage for biasing each of the transistors of the RF power device. This bias voltage is combined with a programmable D.C. offset voltage. The values of the constant current and D.C. offset voltage are programmed such that the average of the quiescent collector currents of the parallel-connected transistors of the RF power transistor corresponds to the quiescent collector current through the temperature-sensing transistor. An optional external control voltage may be used to further adjust the bias voltage for the RF power transistor.