A new design and performance-test strategy for sigma-delta modulators

The paper proposes a new approach to sigma-delta modulator design based on linear and non-linear control theories combined with a number of digital signal processing techniques. The limitations of single-stage high-order designs ar analyzed as a compatibility problem between the linear filtering and non-linear quantiser requirements. The complexity versus performance-improvements of other strategies are also discussed. In addition to the new approach to component-compatibility analysis, the paper proposes a more rigorous analyses of the system performance by using, for the first time, groups of harmonic-rich test signals. Based on this new approach and the extensive analysis of how jointly and severally the linear and non-linear parameters influence the modulator's performance, a new design strategy is proposed and results demonstrated on a single-stage second-oder modulator. The results are compared with those of an already-published second-order design for low over-sampling ratio of 64. It is shown that under the same conditions the new modulator exhibits a significantly improved signal-to-noise-ratio 'response' over a wide dynamic range of input signals. Finally, the conclusion discusses how this approach can be extended to other designs as well as used as a framework to completely new adaptive strategies.