Behavioral Model for RF Power Transistors Based on Canonical Section-Wise Piecewise Linear Functions

A new, frequency-domain, behavioral modeling methodology for radio frequency (RF) power transistors, based on canonical section-wise piecewise linear (CSWPL) functions, is presented in this article. The basic theory of the proposed model for fundamental, harmonic, and dc responses is provided within. Compared with the existing nonlinear behavioral models, which require tables of coefficients to account for varying input powers, the model described in this article is able to predict transistor behavior over the entire Smith chart, at different levels of input power, from the linear region to strongly nonlinear region, with only a single set of model coefficients. Model verification is performed at fundamental, harmonic, and dc frequencies through comparisons with simulated data from a reference nonlinear circuit model and with experimental data from separate 10- and 2-W GaN HEMT devices, over a wide range of load conditions. The models can predict, accurately, the optimal area on the Smith chart for maximum fundamental output power. Furthermore, the ability of the model to interpolate across input power levels is also tested, with excellent fidelity to the simulated and measured data obtained. Compared with a 2-D polynomial-based model, the proposed method provides for a more accurate prediction, while using fewer model coefficients.