Recursive causal convolution [passive distributed circuits]

A new method is presented for implementing discrete numerical convolution in passive circuit simulation which achieves high efficiency by using a recursive formulation. The technique starts with an FIR response obtained by a conventional convolution method and obtains an IIR filter using Pade approximants in the z-domain. The resulting IIR filter is tested for stability using the Lehmer-Schur algorithm and for accuracy by comparing its impulse response to that of the original FIR filter.