Alternative topologies for sigma-delta modulators-a comparative study

This paper investigates four frequently used modulator topologies, namely two single-stage and two multistage architectures. Simple parametric expressions are derived which describe minimum amplifier gain and bandwidth requirements for all implementations as well as C-ratio matching conditions for the two multistage circuits. The cumulative effect of all amplifier nonidealities, including slewing, is revealed by a discrete-time simulator. This study not only presents accurate quantitative results that illustrate the negative impact of the most stringent amplifier nonidealities but also provides the necessary insight to circumvent or minimize these parasitic effects which ultimately limit performance.