Use of surface passivation ledges and local negative feedback to reduce amplitude modulation noise in AlGaAs/GaAs heterojunction bipolar transistors

It is shown that the use of surface passivation ledges and local negative feedback with an unbypassed emitter resistance reduce the AM noise of AlGaAs/GaAs heterojunction bipolar transistors (HBT's). The simultaneous use of both techniques improves the AM noise by 9 dB at 100 Hz offset. The correspondence between reductions in baseband noise and AM noise are described.>