Nonlinear Dynamic Modeling of RF PAs Using Custom Vector Fitting Algorithm

This paper presents an efficient implementation of a first-order modified-Volterra model for radio-frequency power amplifiers. Nonlinear dynamic effects displayed by such systems are described by nonlinear functionals that involve two-variable amplitude-frequency integral kernels. The Vector Fitting algorithm, typically employed for linear systems, is here exploited to provide a decomposition of Volterra kernels into a set of nonlinear static functions of the PA input and corresponding single-pole frequency responses. These are based on a set of global poles that efficiently describe the system dynamics and ultimately lead to a compact model representation. Model implementation results from CAD simulation data are reported for a 6W PA based on a gallium nitride (GaN) transistor.