A SPICE Model for Bipolar Junction Transistor Amplifier Design Verification That Uses Specified DC and Small-Signal AC Parameters Simultaneously

Abstract

This bipolar junction transistor SPICE model was developed to improve students’ confidence in their amplifier analysis and design techniques. The model is used to verify amplifier design calculations that are based on assumed transistor parameters. The model incorporates specifications for the large-signal dc bias circuit and small-signal ac gain simultaneously, including the Early effect. It also accommodates "ideal" assumptions like a particular thermal voltage and base-emitter voltage at the dc quiescent point. The necessary variables of SPICE’s Gummel-Poon bipolar transistor model are computed from the user-specified design and environmental parameters. If the user’s circuit design calculations are correct, the amplifier’s simulated bias point and gain will be nearly identical to the specifications, limited primarily by the numerical precision of the original calculations, readily verifying the design’s accuracy. This modeling technique eliminates the need to use separate dc and small-signal ac simulation models that result from the typical way bipolar transistor theory is applied.