Custom designed high-order frequency transformations for IIR filters

This paper addresses high-order frequency transformation and extends standard Constantinides, Mullis/Franchitti transformations and the exact N-point approach we have previously reported. Using specially designed M^th order allpass filters, mapping of N features of the prototype filter can be carried out independently (where N<M). The mapping filter is designed taking special care to ensure that there are no excess mapping replicas which may arise if an exact N-point transformation is used. This design viewpoint represents a significant departure from previous approaches to filter transformations