A Design Procedure for Stable High Order, High Performance Sigma-Delta Modulator Loopfilters

Abstract

In this paper we present the ideas for design of stable high order single bit sigma-delta modulator loopfilter transfer functions that provide high signal-to-noise ratio. The procedure is backed up with example and results made for third order loopfilter sigma-delta modulators and give the performance impact on them when varying the poles of the noise transfer function, when using optimized zeroes. This loopfilter function design is computed with fast theoretical calculation of the signal to noise ratio with mathematical formula, instead of approximation based on simulations and combined with theory that presents approximated value for modulator’s maximal stable DC input signal, resulting in design without the need of simulations of the modulator output bitstream.