Large-signal modelling including low-frequency dispersion of n-channel SiGe MODFETs and MMIC applications

Abstract

This paper presents a circuit-design oriented, large-signal model for n-channel SiGe MODFET transistors, its application to the design of mixer and amplifier MMICs as well as measurement results. The model is based on an equivalent circuit approach and employs robust, globally continuous equations to describe the non-linear circuit elements. All transistor operating regions are covered without the use of partially defined equations or smoothing functions. Significant low-frequency dispersion effects similar to those found in III–V HEMT devices are observed and incorporated in a large-signal dispersion model. The bias dependency of the gate–drain and gate–source capacitance is extracted and modelled, allowing for verification of the model for frequencies up to 50 GHz. Based on the presented transistor model, an active FET mixer MMIC and a travelling-wave amplifier using the SiGe MODFET technology are designed and good agreement between simulation and measurements is achieved.