Optimization based passive constrained fitting

Verification of contemporary integrated circuits requires accurate modeling of high frequency effects in all passive component subsystems. Often, descriptions of those subsystems are only available in the frequency-domain. In this paper, we propose a simple, scalar, constrained-passive rational approximation scheme that incorporates a grid-based test for strict positive realness. In contrast to similar recent work based on convex optimization and the positive real lemma, the methodology is potentially more efficient, since it does not introduce a quadratic number of auxiliary variables, is potentially more accurate, since pole locations can be re-adjusted during the optimization, but possibly less reliable, since it relies on the solution of optimization problems that are not convex. Therefore, because of the use of local constrained non-convex optimization, the generation of feasible initial guesses is also considered.