A BJT model with self heating for WATAND computer simulation

Abstract

A brief overview of bipolar junction transistor (BJT) modeling is presented. Two macromodels based on the Gummel-Poon model are designed to simulate npn and pnp BJT performance including self heating. The self-heating models calculate BJT junction temperature, account for temperature dependency in the modeling equations and give automatic adjustment to temperature-variant parameters including the saturation current (Is) and the forward current gain (ß ). Two external thermal equivalent circuit nodes make it possible to connect improved and more complete thermal equivalent models. A 2N2222 model based on the npn macromodel is developed and used for testing. Common-emitter and mirror current circuits are used to test the models. Experimental results for the thermal steady-state and transient responses are compared with WATAND and PSPICE analysis using the self-heating and nonthermal models of the 2N2222 transistor. For the self-heating model, the error with respect to steady-state experimental data is less than 7%. For the nonthermal models, the error is up to 84%. As temperature increases, error also increases. The self-heating model tracks the thermal transient response correctly, while the nonthermal model shows no thermal transient response. The self-heating model is also used to test the temperature stability of the mirror current circuit fabricated on an IC chip.