Model-Based Nonlinear Embedding for Power-Amplifier Design

Abstract

A fully model-based nonlinear embedding device model including low- and high-frequency dispersion effects is implemented for the Angelov device model and successfully demonstrated for load modulation power-amplifier (PA) applications. Using this nonlinear embedding device model, any desired PA mode of operation at the current source plane can be projected to the external reference planes to synthesize the required multi-harmonic source and load terminations. A 2-D identification of the intrinsic PA operation modes is performed first at the current source reference planes. For intrinsic modes defined without lossy parasitics, most of the required source impedance terminations will exhibit a substantial negative resistance after projection to the external reference planes. These terminations can then be implemented by active harmonic injection at the input. It is verified experimentally for a 15-W GaN HEMT class-AB mode that, using the second harmonic injection synthesized by the embedding device model at the input, yields an improved drain efficiency of up to 5% in agreement with the simulation. A figure-of-merit is also introduced to evaluate the efficacy of the nonlinear embedding PA design methodology in achieving the targeted intrinsic mode operation given the model accuracy.