D.C.-parameter characterization of the early effect in bipolar junction transistors

The effects of base width modulation (`Early effect¿) on the d.c. and low-frequency incremental output characteristics of a bipolar junction transistor are reviewed critically, using only a basic consideration of the physical electronics of device operation. Attention is focused on the dependence on collector-base voltage of the majority carrier charge in the base of a device having an arbitrary base doping distribution. The conditions under which a single voltage parameter (`Early voltage¿) can be used to describe the output characteristics, independent of baseemitter drive conditions, are examined and some implications of the results to the circuit engineer outlined.