PA design and statistical analysis through X-par driven load-pull and EM simulations

Modeling the active device is a key step for the successful statistical analysis of power amplifiers: the nonlinear model must not only depend on the most relevant device fabrication parameters, but should also work accurately in source/load-pull analysis, since variations of the passive embedding network effectively act as a load-pull at the active device ports. We demonstrate that the X-parameter model extracted from physics-based nonlinear TCAD simulations is extremely accurate for load-pull analysis. The X-parameter model is coupled to electromagnetic simulations to assist the variability-aware design of a GaAs MMIC X-band power amplifier (PA): concurrent variations of the active device doping and of the capacitor dielectric layer thickness are considered as the main contributions to PA variability. Two possible output matching networks, with distributed or semi-lumped design, are compared: already for moderate doping variations the PA output power spread is dominated by the active device variability, while passive network variations are always the relevant contribution to PA efficiency.