Harmonic Balance with Small Signal Perturbation

Investigating perturbations of a periodic steady state of an electric circuit is of interest e.g. for small signal responses, noise analysis or the generation of X-parameter models. We present a method based on Harmonic Balance, to compute the Fourier coefficients of the circuit response for a small signal perturbation of the input. The relation to two-tone Harmonic Balance is investigated and it is shown that under suitable conditions the perturbation method can approximate the full two-tone solution at extremely lower costs. The method is tested on a Gilbert mixer circuit.