Effect of Reverse Base Current on Bipolar and BiCMOS Circuits

Abstract

This paper presents a detailed study on the effect of reverse base current (RBC) on the switching behavior of bipolar BiCMOS circuits utilizing advanced high-performance bipolar transistors. It is shown that as the collector doping Ncis increased to overcome the Kirk effect (base stretching) during the switching transient, the avalanche-generated reverse base current in the collector-base junction may cause problems for bipolar output devices switching out of saturation. A basic bipolar inverter and various BiCMOS driver circuits were simulated based on measured avalanche multiplication factors from advanced bipolar transistors with various collector doping Nc. In the case of the basic bipolar inverter, the reverse base current may prevent the switching device from being shut off completely during the on-to-off transition and a self-sustained state may result which reduces the output voltage swing. For the common-emitter (CE) BiCMOS driver, a similar self-sustained state may also occur with the added adverse effect of excessive leakage in standby. The design and scaling considerations of the devices and circuits are discussed. © 1992 IEEE