Patent ID: 7772927

Claim:
A circuit comprising: a first bipolar transistor element comprising: a first emitter; a first base; and a first collector adapted to provide a radio frequency (RF) output signal; a second bipolar transistor element comprising: a second emitter coupled to the first base; a second base adapted to receive an RF input signal; and a second collector coupled to the first collector; and feedback and active bias circuitry: adapted to: sense bias conditions at the first emitter via a bias sense input; sense RF output conditions at the first collector via an RF output sense input; and provide bias and feedback to the second base via a feedback and bias output based on the bias conditions and the RF output conditions; and comprising a feedback network and a feedback filter coupled in series between the feedback and bias output and the RF output sense input, such that the feedback network provides feedback to the second bipolar transistor element and the feedback filter provides frequency dependent feedback to the second bipolar transistor element, wherein the first and second bipolar transistor elements form a Darlington amplifier adapted to amplify the RF input signal to provide the RF output signal.