An Exact Circuit Analogue of Transistor Alpha†

Abstract

This paper describes an exact circuit analogue of the theoretical expression for the current amplification factor a of a junction transistor, obtained by solving the one-dimensional diffusion equation. It consists of an exponentially tapered RC transmission line, driven by a current generator and terminating in a capacitor. With proper choice of the source current, the line parameters and the load capacitance, the expression for the output current is exactly the same as that for a, deduced from a consideration of the physics of transistor action. On the basis of the above circuit analogue, the frequency variation of the collector conductance g c and collector capacitance C c are examined and the results are compared with those obtained from earlier circuit models for α.