Efficient polyphase decimation filter

Abstract

An efficient polyphase half rate finite impulse response (FIR) filter module includes an odd/even sample delay line. The odd/even sample delay line includes two parallel paths of delays corresponding respectively to odd and even sample processing, i.e., every other sample. A first input sample is presented to the first register phase in the odd/even sample delay line and is fed directly to the third register phase bypassing the second register phase, the third register phase feeds directly into the fifth register phase, and so on until the ninth register phase of the odd/even sample delay line feeds directly into the eleventh register phase bypassing the tenth register phase. A second input sample skips over the first register phase and is presented directly to the second register phase in the odd/even sample delay line. Thereafter, the second register phase feeds directly to the fourth register phase, and so on until the tenth register phase of the odd/even sample delay line feeds directly into the twelfth register phase bypassing the eleventh register phase. A plurality of polyphase half rate filters may be serially combined to provide the desired decimation rate. The bit width of sub-products in a polyphase math logic module is reduced from that in conventional FIR filter math logic modules to allow faster clocking of the FIR filter.