Impact of the emitter stored charge on RF noise of junction bipolar transistors

In this paper a new noise model is presented which accounts for the effect of the emitter stored charge on the RF noise behavior of bipolar junction transistors. The model is derived combining the general Van Vliet noise model for bipolar transistors and the non-quasi-static (NQS) theory in quasi-neutral base and emitter regions. Model equations are then interpreted with the help of a small-signal equivalent circuit of a bipolar transistor which includes additional circuit elements in order to take the NQS effects in the base and in the emitter into account. It is shown finally that the emitter diffusion charge can have a considerable impact on the noise FOM´s of bipolar transistors, compared to the impact of the NQS effects in the quasi-neutral base region.