Early effect modeling in SPICE

The approximations made in the Early effect formulation of the SPICE Gummel-Poon bipolar junction transistor (BJT) model were reasonable when the model was first developed but introduce unnecessary inaccuracies when modeling the output conductance of modern BJTs. In this paper, we give the reason the original approximations were made, present a new way to plot data to best show the Early effect, and detail a new, consistent, coupled method to determine forward and reverse Early voltages.