Symbolic pole/zero calculation using SANTAFE

The aim of symbolic analysis is to gain insight into circuit behavior. Therefore, in general, the location of the poles and zeros has to be known, which cannot be calculated symbolically for polynomials with degree greater than four. The CAD tool SANTAFE (Symbolic Analysis of Transfer Functions) applies the signal-flow graph method which tries to keep the result in a factorized form. The graphic view provided by a signal-flow graph is more visual and, as will be demonstrated, enables the user to perform circuit knowledge based approximations. A novel procedure based on symbolic Newton iteration accurately calculates high order transfer functions in the desired pole/zero form. In this way an Op-Amp was realized in a 1 ??m 4 GHz BiCMOS process.