Filter structures composed of all-pass and FIR filters forinterpolation and decimation by a factor of two

摘要

This paper introduces filter structures for interpolation andndecimation by a factor of two. The structures are derived by using thenfrequency-response masking approach, in which the overall filter makesnuse of a periodic model filter, its complementary filter, and twonmasking filters. The periodic model filters are obtained by replacingneach delay element in a model filter with M delay elements in cascade.nThe model filter is a half-band infinite-impulse response (IIR) filterncomposed of two all-pass filters in parallel, whereas the maskingnfilters are linear-phase finite-impulse response (FIR) filters. In thenfinal interpolator and decimator structures the filtering takes plate atnthe lowest of the two sampling rates involved. The corresponding overallnfilter can be designed by separately optimizing a half-band IIR filternand a linear-phase FIR filter. Both nonlinear-phase and approximatelynlinear-phase filters are considered. One advantage of the proposednfilter structures over conventional half-band IIR filter structures isnthat their maximal sample frequency is M times higher, which may benutilized to increase the speed in an implementation and/or to reduce thenpower consumption via power supply voltage scaling techniques. In thencase of approximately linear-phase filters, the computational complexityncan be reduced as well. Several design examples are includedndemonstrating the properties and advantages of the proposed filternstructures