CONSISTENCY IN MODELING THE EARLY EFFECT IN BIPOLAR TRANSISTORS.

Extended Ebers-Moll models of bipolar junction transistors have proven useful in computer-aided design packages for many years. The most recent refinement has been the incorporation of base-width modulation or Early effect through a single model parameter called the Early voltage. This paper delineates the conditions under which a unique Early voltage can be defined and shows that a necessary condition is the base current must independent of collector-emitter voltage. Further, a linearization of the large-signal model around a dc operating point leads to a small-signal hybrid-pi model in which the collector-base resistor r//u is necessarily absent. The absence of r//u has many implications in the design of high performance amplifier circuits.