SiGe HBT's Small-Signal Pi Modeling

This paper presents the derivation procedure used in determining the parameters in SiGe HBT's small-signal model where the Pi circuit configuration is employed. For both the transistor's external base-collector capacitor and its base spreading resistor, new close-form expressions have been derived. Comparisons with existing approaches vindicate the feasibility and effectiveness of our formulations. With the impact of the lossy substrate effectively modeled and the frequency dependency of the transconductance properly addressed, this proposed extraction approach demonstrates accurate results up to 30 GHz with different bias conditions.