A comparison of various low-pass filter architectures for sigma-delta demodulators

Abstract

A comparison of various low-pass filter architectures that are commonly used in Sigma-Delta(/spl Sigma/-/spl Delta/) demodulators is presented in the paper. In this comparison the conventional demodulator filter architectures such as the optimal FIR filter, Sinc/sup k/ filter and non-linear Zoomer filter are considered. It is shown that the optimum FIR filter provides the most attractive properties among the conventional demodulator low-pass filters. As an alternative to the optimal FIR filter, optimal Laguerre IIR filter architecture is then proposed in the paper. A design scheme for the optimal IIR filter is presented via the use of orthonormal Laguerre functions. In comparison with the conventional FIR filter approach, this design offers several attractive features. The proposed IIR filter design problem is easy to solve and numerically robust. Furthermore, the optimal IIR filter is easy to implement because it needs only a small number of components and therefore well suited for VLSI implementations.