In this article

it is first shown that two fundamental parameters

the voltage-feedback coefficient η under constant collector current and the current-feeback coefficient σ under constant base-emitter voltage are most suitable for a complete and rigorous description of the Early-effect of a transistor

and the low-frequency small-signal circuit parameters can readily be derived from them.For the general case where the impurity profile in the base region is arbitrary

η can be expressed in terms of the effective base-doping charge Qb and the transition capacity Cc of the collector junction

and a can be expressed in terms of Qb and the base transit time tb of the transistor. For a planer transistor with a Gaussian base-doping profile

a series of graphs is given

available for evaluating η

σ

Cc

tb and other small-signal circuit parameters. The case of a lateral pnp transistor is also discussed

and a numerical example is given. This article is ended with a brief discussion of the so-called Early-voltage and its relation to coefficients η and σ.