A multistage closed-loop sigma-delta modulator (MSCL)

A new family of high order Sigma Delta modulators called MSCL (Multi Stage Closed-loop) is presented in this paper. They use a global feedback to lower the sensitivity to circuit imperfections. This feedback from the output of the modulator is the sum of the output of each comparator so that no digital prefiltering is required before summing up these signals. However, easy calibration will be required to compensate for the feedback imperfections. MSCL modulators present the same insensitivity to circuit imperfections as classical multi-order one-bit converters, but reach the performance of high-order MASH (MultistAge noise SHaping) modulators. They help make high-order low-pass or band-pass modulators without limit cycles so that their quantizing noise characteristics are similar to those predicted by the linear simplified model.