ALTERNATIVE TOPOLOGIES FOR SIGMA-DELTA MODULATORS - A COMPARATIVE-STUDY

This paper investigates four frequently used modulator topologies, nam ely two single-stage and two multistage architectures. Simple parametr ic expressions are derived which describe minimum amplifier gain and b andwidth requirements for all implementations as well as C-ratio match ing conditions for the two multistage circuits, The cumulative effect of all amplifier nonidealities, including slewing, is revealed by a di screte-time simulator, This study not only presents accurate quantitat ive results that illustrate the negative impact of the most stringent amplifier nonidealities but also provides the necessary insight to cir cumvent or minimize these parasitic effects which ultimately limit per formance.