Continuation method in multitone harmonic balance

Design of communication circuits often requires computing quasi-periodic steady state response to multiple inputs of different frequencies that may not always be harmonically related. Multitone harmonic balance method can be used to provide an accurate solution if the circuit is mildly nonlinear. However, the convergence of harmonic balance methods is not guaranteed if the initial guess is far from the actual solution. We present a novel approach to apply continuation method in multitone harmonic balance to significantly improve the convergence properties of this technique. In addition to being more robust, we show that the continuation based method can be significantly more efficient in terms of run-time compared to traditional fixed step source-stepping methods. Simulation results on strongly nonlinear circuits are used to illustrate the effectiveness of the algorithm.