Abstract: The response of linear and non-linear systems to an arbitrary pulse train is modeled for efficient and accurate circuit simulation. First, a harmonic balance analysis is performed for a system incorporating linear and non-linear components. Then, the even and odd frequency components of the harmonic balance result are separated and interpolated. Finally, the resulting interpolated components are combined to generate the frequency domain positive step response and the frequency domain negative step response of the system. These resulting frequency domain step responses are utilized to generate a low order pole/zero model of the step responses. The pole/zero model can then be used to efficiently and accurately model the response of the system to an arbitrary sequence of positive and negative going pulses.