Nonlinear simulation of digital RF transmitters under modulated excitation

A technology push towards digital radio frequency (RF) transmitters (DRFTx) is all apparent due to the many beneficial properties they offer. However, their distortion mechanisms pose a challenging problem for practical realizations. To a significant extend this is caused by the nature of the excitation signal. DRFTx are driven by a binary signal with rates in the Gbit/s domain and only a fraction of this signal constitutes the desired modulated RF output. All other signal components are required to achieve an energy efficient operation of the DRFTx´s PA stage. Such significant cross dependencies call for nonlinear simulations that predict the behavior of a circuit in question. This paper addresses this issue by demonstrating a method that allows to predict a DRFTx´s output time-domain waveform in a computational efficient manner. The underlying nonlinear model is based on readily available nonlinear transistor models within RF computer aided design (CAD) tools. Additionally this simulations are compared to measurements of the same amplifier in a lab setup.