High-frequency noise modelling and the scaling of the noise parameters of polysilicon emitter bipolar junction transistors

This paper presents detailed results from modelling the four noise parameters: minimum noise figure (NF MIN ), noise resistance (R N ), optimal source resistance (R S,OPT ), and reactance (X S,OPT ) as functions of frequency and collector-biasing current. Compared to previous BJT (bipolar junction transistor) high-frequency noise models, we include the emitter resistance, which results in an increased input device impedance, and a degeneration of the device transconductance. We also give an explicit formula for the noise resistance. We present noise results for polysilicon emitter bipolar transistors as a function of emitter areas to demonstrate how the noise parameters scale with emitter areas over a range of frequencies. However, these results are given only for devices in which the pad impedances are much larger than the device input impedance, so that very little input signal is lost through the pads to ground.