Modeling phase and amplitude noise in heterojunction bipolar transistor amplifiers

In this paper we present a numerical noise model for heterojunction bipolar transistor (HBT) amplifiers and use it to predict the phase modulation (PM) and amplitude modulation (AM) noise sensitivities to low-frequency current noise in linear microwave HBT amplifiers. The model predicts that at carrier frequencies close to the amplifier´s 3-dB frequency the AM noise sensitivity decreases with increasing current and with increasing carrier frequency. In addition, at these carrier frequencies the PM noise sensitivity does not show a simple dependence with current, but it varies with carrier frequency, and transistor and circuit parameters. Furthermore, at low carrier frequencies the PM noise sensitivity increases with increasing carrier frequency, at around the 3-dB frequency it reaches a maximum then it decreases with carrier frequency.