Nonlinearities in the Base Emitter Junction of Heterojunction Bipolar Transistors

Abstract

The nonlinear behaviour of the base emitter junction in HBTs is investigated.Nonlinearities cause troublesome distortion and intermodulation of signals and raise the bit error rate. They are therefore a key issue in microwave communication systems.Hewlett-Packard's Microwave Design System (MDS) software package has been used to simulate these phenomena. The simulation results are verified by an analytical method called nonlinear current method which is a derivative of the Volterra series approach. With the aid of this method new analytical expressions are derived that provide insight into the subtleties of nonlinear phenomena. These expressions are evaluated by the program MAPLE and subsequently compared with the MDS results. Two different models for the B-E junction are juxtaposed. The derived equations reveal the identity and correspondence between the two models.Finally, this thesis also addresses harmonic balance simulation which is the type of simulation MDS employs to simulate nonlinear circuits.