In this paper, a method to design and implement a very efficient multistage
decimation filter for a sigma-delta (Sigma Delta) A/D converter is propose
d. The scheme is composed by two stages, but the proposed method can be eas
ily extended to a multiple-stage implementation, The first-stage filter is
obtained by properly rotating the zero-pole distribution of a comb filter i
n the z-plane, The obtained structure exhibits linear phase and can be impl
emented by using a recursive structure with only two multipliers, The desig
n phase is easy and very flexible. As most of the quantization noise is eli
minated at the first stage, the second-stage filter can be designed with re
laxed specifications. Any classical design algorithm can be used for it. An
alternative scheme for the second stage can be obtained by splitting the s
tage into two substages, and the method proposed in this paper can be itera
ted.
The system performances are evaluated by simulation.