Exact design of multirate switched-current FIR filters with improved phase linearity

The design of linear phase multirate FIR filters for switched-current decimators is presented. The question of finding the decimating factor M for a given filter order N, as function of the timing used, is discussed. It is shown, that exact linearity can be achieved only for special cases of M and N, and that it depends on the chosen timing. Furthermore, we show that modulo arithmetic is a useful tool for analyzing multirate systems.