I. Introduction
Advanced silicon-based BiCMOS technologies now offer Silicon-Germanium (SiGe) heterojunction bipolar transistors (HBTs) with operating frequencies beyond 350 GHz [1]. Those technologies are expected to mature over the next couple of years and thus, will enable the implementation of ultra high-frequency (h.f.) applications, such as mm-wave imaging and 160 Gb/s fiber optic transmission. Experience shows that cost and design of h.f. front-end circuit modules represent a significant bottleneck for the implementation of the overall system. This require models for circuit simulation, so-called compact models (CM), that very accurately capture the device characteristics over a wide bias, frequency, temperature and geometry range, including non-standard characteristics such as noise and distortion that are of high importance for h.f. applications [2].