Electrothermal models of transistors based on finite element analysis for radar applications

Electrothermal models of power devices are necessary for an accurate analysis of their performances. For this reason, this paper deals with the methodology to obtain an electrothermal model based for its thermal part on a reduced model of a three dimensional Finite Element (FE) thermal simulation and on electrical measurements for its electrical part. The reduced thermal model is based on a Ritz vectors approach and its equivalent SPICE subcircuit implementation. The complete model has been successfully implemented in the Advanced Design Simulator (ADS) for two kind of X band power amplifiers of 8 W class. One is based on TRIQUINT PHEMT transistors and the other on UMS HBT transistors. Coupled to a distributed electrical model, this electrothermal model has been used in order to investigate the behavior of these two High Power Amplifiers (HPAs) during radar pulses.