Non-linear Modeling of a Multi-FET Multi-Port IC

A method is presented for developing a large-signal MESFET model for a compact multi-FET and multiport GaAs IC, which is employed in a 2 GHz hybrid power amplifier. The approach employs Agilent (formerly HP) EEsof??s IC-CAP?? computer-aided measurement acquisition and parameter extraction software. IC-CAP is used to develop conventional Curtice Cubic MESFET models for the constituent FETs. The interesting aspects of the work are the multi-port nature of the IC, and the inability to derive suitable device characterization measurements directly from the multi-FET IC. Our approach was to model individual ??dropout?? devices that are similar, though not identical to, the devices comprising the IC. The composite multi-FET non-linear model has more than six accessible ports to which, ground connections, package parasitics, biasing and matching networks are connected to enable simulation of the entire power amplifier. Individual FET model parameters are extracted from swept DC and small-signal S-parameter measurements. Linear transformations and regression algorithms within the IC-CAP software facilitate parameter extraction. Measurements and subsequent large-signal models were made of three individual MESFET devices, with gate widths of 300??m, 1200??m and 7200??m, representative of those that comprise the MMIC power amplifier. Additional measurement challenges included the relatively high power output, and current of the largest FET device. Exploration of accuracy and limitations of the non-linear models was carried out with linear and non-linear measurement and model comparisons.