Passive macromodeling of one-port immittances via direct rational fitting of spectral factors

In this paper, we propose an algorithm for the generation of guaranteed passive state-space models of one-port immittances from finite frequency response samples. Differently from conventional approaches, which are based on a two-step process that first fits a rational function to the samples, and only in a second stage checks and enforces passivity via perturbation, our approach provides directly a guaranteed passive model. This is achieved by computing a stable rational approximation of a spectral factor associated to the immittance function under modeling. Several examples demonstrate the feasibility of the proposed technique.