IIR Approximation of FIR Filters Via Discrete-Time Hybrid-Domain Vector Fitting

We present a discrete-time hybrid-domain vector fitting algorithm, called HD-VFz, for the IIR approximation of FIR filters with an arbitrary combination of time-and frequency-sampled responses. The core routine involves a two-step pole refinement process based on a linear least-squares solve and an eigenvalue problem. Through hybrid-domain data approximation and digital partial fraction basis with relative stability consideration, HD-VFz exhibits fast computation and remarkable fitting accuracy in both time and frequency domains.