High-speed recursive digital filters based on the frequency-response masking approach

The frequency-response masking approach for highspeed recursive infinite-im pulse response (IIR) digital filters is introduced. In this approach, the o verall filter consists of a periodic model filter, its power-complementary periodic Filter, and two masking filters. The model filters are composed of two all-pass filters in parallel, whereas the masking filters are linear-p hase finite-impulse response (FIR) filters. The transfer functions of the a ll-pass filters are functions of z(M), which implies that the maximal sampl e frequency for the overall filter is M times that of the corresponding con ventional IIR filter The maximal sample frequency can be increased to an ar bitrary level for arbitrary band-widths. The overall filter can be designed by separately optimizing the model and masking filters with the aid of con ventional approximation techniques. The obtained overall filter also serves as a good initial filter for further optimization. Both nonlinear-phase an d approximately linear-phase filters are considered. By using the, new appr oach, the potential problems of pole-zero cancellations, which are inherent in algorithm transformation techniques, are avoided. Further, robust filte rs under finite-arithmetic conditions can always be obtained by using wave- digital all-pass filters and nonrecursive FIR biters, Several design exampl es are included illustrating the properties of the new filters.