Ring oscillator circuit simulation with physical model for GaAs/GaAlAs heterojunction bipolar transistors

Switching performance is simulated for GaAs/GaAlAs heterojunction bipolar transistors (HBT's) by combining a realistic physical device model that involves numerical solutions for carrier transport equations and Poisson's equation with a circuit simulator that enables direct access to the device model embedded in arbitrary circuits. Based on simulated results for five-stage ring oscillators, discussion is given as to how the switching performance depends on the circuit configuration such as current mode logic (CML) without and with emitter follower, and direct-coupled transistor logic (DCTL), inclusion or exclusion of external base areas, and choice for single- or double-heterojunction transistors.