Multirate IIR filter structures for arbitrary bandwidths

This paper introduces new multirate infinite-length impulse-response (IIR) filter structures for arbitrary bandwidths. The overall filters have the same input and output sample rates. Multirate techniques are only used internally in order to improve the efficiency. The overall filters make use of an IIR filter for the actual filtering, periodic allpass filters for constructing complementary filters, and linear-phase finite-length impulse-response (FIR) filters for the sampling rate alterations. There are the following two main reasons for introducing the new filters: 1) they can be used to obtain so called high-speed IIR filters (i.e., filters able to operate at a high sample rate) with lower complexity than that achievable with single-rate high-speed filters and 2) they can be used to obtain approximately linear-phase filters with substantially lower complexity than that achievable with single-rate filters. The overall filters are designed by separately optimizing a number of linear-phase (possibly half-band) FIR filters, and one IIR filter being realizable as a parallel connection of two allpass filters. Design examples are included illustrating the usefulness of the proposed filters.