Efficient modeling and simulation of nonlinear amplifiers

Traveling-wave tube amplifiers (TWTAs) and solid-state power amplifiers (SSPAs) are used in many communication systems and exhibit nonlinear distortions in both amplitude (AM/AM) and phase (AM/PM). In general, a TWTA or SSPA is part of an overall communication system that consists of other elements, such as a pulse-shaping filter. The analytical study of a system consisting of linear and nonlinear devices is often intractable and thus simulation is usually used to determine performance of such systems. An important aspect in the simulation of a nonlinear system is the selection of the sampling rate. The sampling rate must be sufficiently high to avoid aliasing distortion due to spectrum folding, which degrades the fidelity of the simulation. However, at the same time, the sampling rate should be set low to reduce computation burden and minimize simulation times. A systematic way to determine the sufficient (or optimal) upsampling factor for simulation of a communication system with a nonlinear system and a pulse-shaping filter will be presented. The tradeoff between fidelity and speed of communication system simulation will be shown. We will also show how a nonlinear system can be implemented using a hardware co-simulation technique