An improved small-signal model for SiGe HBTs

Accurate equivalent-circuit modelling is a prerequisite for the circuit design. In this article, an improved small-signal equivalent-circuit model for silicon-germanium heterojunction bipolar transistors (SiGe HBTs) is proposed. The proposed model has taken into account the effects of the base and collector metallisations, and the corresponding extraction method of the substrate elements is developed. The extraction approach is validated with SiGe HBTs fabricated with a 0.35-μm BiCMOS technology, 1 × 8 μm² emitter area from 50 MHz to 10 GHz. The agreements between the measured and modelled data are excellent in the desired frequency range over a wide range of bias points with different bias conditions.