Small-Signal Model Verification and Analysis of Unmatched Multi-Finger HBT Cells at 220 GHz

In this paper we verify the small-signal performance and simulation accuracy of two common-emitter (CE) and one common-base (CB) multi-finger heterojunction bipolar transistor (HBT) cells used in power amplifier designs at 220 GHz. We first verify the accuracy of the manifold simulation, the structure connecting multiple HBTs together, using passive structures that comprise the manifold before verifying the accuracy of the single-finger model and the four-finger cell simulation. We find that the discrepancies between simulation and measurement of the four-finger cell tends to be the same as or lower than the discrepancies in the single-finger device from140 - 230 GHz. The simulation accurately predicts the gain of all cells and the reflection coefficients of the CB cell. However, there are discrepancies between simulated and measured reflection coefficients of both CE cells, with a difference in linear magnitude greater than 0.1, and discrepancies with the measured stability factor of the CB cell.