New envelope-currents method for the Simulation of weakly nonlinear communication circuits

In this paper, a novel approach to analyze weakly nonlinear microwave circuits excited by digital communications signals is reported based on a recursive algorithm. The method analyzes a time-varying linear circuit excited by appropriate nonlinear currents (NCs) with node waveforms updated in each iteration. Simulation results are compared with harmonic balance and NC methods, showing fast convergence properties and accuracy even with only one iteration. The extension of the algorithm to the envelope-currents method gives a procedure to analyze the effects of nonlinear distortion in the case of excitation with communications signals. This approach allowed the evaluation of the spectral regrowth and adjacent channel power ratio of a MESFET amplifier at 2 GHz, with simulation results showing a good agreement with measurement data.