Event-driven simulation of Volterra series models in SystemVerilog

This paper presents a method to simulate the behavior of a weakly-nonlinear analog circuit in a digital logic simulator like SystemVerilog. To our knowledge, this is the first report on a true event-driven simulator that can compute the nonlinear circuit response modeled with a Volterra series. The core idea is to express a continuous-time signal as a linear combination of basis functions, t^m exp(at)·u(t), which was previously demonstrated for linear systems. To extend this approach to nonlinear systems, a Volterra series model is reformulated into a set of linear differential equations each corresponding to a different-order component of the nonlinear system response and describing the contribution of the initial condition explicitly. The presented simulator is demonstrated on the cases of estimating the spectral regrowth of a RF power amplifier and distortion-induced eye-opening reduction in a continuous-time linear equalizer. Compared to a commercial SPICE simulator, the proposed simulator achieves 300~1000× speed-up in performing timedomain simulations with the same level of accuracy.