An Improved VBIC Large-Signal Equivalent-Circuit Model for SiGe HBT With an Inductive Breakdown Network by $X$ -Parameters

In this paper, the X-parameter measurements are applied first to establish an improved vertical bipolar inter-company (VBIC) large-signal equivalent-circuit model for silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs), which can accurately describe novel and unusual characteristics of inductive behavior at breakdown that can occur in the active region under large-signal drive. This improved VBIC model presented here for SiGe HBTs is modified by incorporating a nonlinear base-collector junction breakdown network to account for the RF avalanche delay effect in the breakdown region. Good agreement between simulated and measured X-parameters, which contain small-signal S-parameters, large-signal spectrum, and hot S-parameters, is achieved, validating the presented large-signal VBIC model in the breakdown region. The determined breakdown inductance and resistance agree well with the theoretical results. This modified model can be used to describe and predict RF large-signal performance accurately when transistors are operated in the breakdown and active regions.