Voltage- and current-dependent model for the base resistance of bipolar transistors

A physical model for the variation of the base resistance of bipolar transistors as a function of operating current, base-emitter voltage, and base-collector voltage, compatible with CAD (computer-aided design) programs, is presented. The model is based on the solution of the free-carrier distribution within the base and collector regions under low- and high-level injection conditions as well as the solution of base-width modulation due to the Kirk effect and the Early effect. The model has been implemented in the WATAND circuit simulator and the agreement between simulations and computed base resistance using the BIPOLE program is shown to be very good