Automated Design of Sigma-Delta Modulators with FIR Feedback

In this paper the heuristic-search based design of Sigma-Delta modulators with FIR feedback is described. Using single-bit quantizers in Sigma-Delta modulators (SDMs) is very common due to their inherent linearity. However, their binary feedback increases the requirements for the integrators and the jitter sensitivity in the loop compared to multi-bit feedback. FIR feedback tries to resolve these problems, however, requires a second compensating FIR filter and an adjusted loopfilter scaling in order to restore the original noise transfer characteristic. This not only makes the design process more challenging but also leads to increased peaking of the STF, undesirable for many applications. Therefore, in this work a heuristic-search based design approach is presented which offloads work from the designer to an automated design environment. It allows to design CT SDMs directly in the CT domain including the compensation of nonidealities and STF engineering in order to counteract the peaking. The theoretical background is described as well as the additions to the underlying design framework. Alongside, design examples are given to illustrate the advantages of this approach.