Revisiting the analytic theory of p-n junction impedance: Improvements guided by computer simulation leading to a new equivalent circuit

We revisit the analytic derivation of the de and low frequency ac behavior of the p-n step junction and suggest all preexisting treatments are flawed for three important reasons, First, not all contributions to the diode curr ent are included. We derive a rigorous expression for each component of cur rent that can be used to judge the completeness of existing analytic theori es. Additionally, wrong boundary conditions for minority carrier concentrat ions and incorrect equivalent circuit topologies undermine present analytic theories of the diode. We propose a new analytic equivalent circuit model which institutes correct boundary conditions. The resulting circuit model d emonstrates excellent de and ac accuracy for symmetric and asymmetric junct ions, for long, short, or intermediate base regimes, Inductive behavior ass ociated with short base diodes at large forward bias is reproduced, as is t he decrease in capacitance observed in long base diodes. The assumptions an d limitations of our new circuit model are thoroughly investigated.