Techniques for nonlinear high-frequency circuit-level simulation

New modes of high frequency circuit operation may involve severe nonlinearity and extensive use of digital control or mixed-signal waveforms together with microwave carriers which in combination present significant challenges for simulation. Much progress has been made in simulation techniques in recent years and this is reviewed briefly, indicating a few limitations and still outstanding challenges. Some features of an in-house transient simulator are outlined, which has proven robust and accurate even for the most challenging applications.