Single OpAmp Higher-Order Filters in Sigma-Delta Modulators

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The aim of the proposed project is the analysis, simulation, and error correction in Sigma Delta modulators (SDM) with higher-order loopfilters realized by a smaller number of - in the extreme case of a single - operational amplifier.This technique was used in discrete filters decades ago to save active components. In SDM it gas been used for several years now, and the pure reduction of the number of operational amplifiers is stated as the advantage; but this should be questioned more generally and in more detail: in a loop filter of a SDM all operational amplifiers have completely different requirements on dynamic range, linearity, noise, speed, etc. so that the implementation of a higher-order filter with a single operational amplifier rapidly leads to extremely high demands on the single amplifier component which cannot at all be realized or only at great expense.In addition, SDM are nowadays often used in continuous-time implementation for wireless receivers, in which the signal transfer function within and outside the inband is crucial. A modification of the signal transfer function can be achieved both at the architectural level, as well as by adding additional (digital) filters in the SDM loop. This possibility is no longer available in the said higher order filters with only one or a few operational amplifiers.Therefore, the proposed project will be devoted to both the general analysis of SDM with higher order loop filters implemented with one or a few operational amplifiers. Sensitivity analysis concerning amplifier non-idealities, modeling of these non-ideal filters, possible compensation schemes for the non-ideal filters at the architectural level, both by analytical methods and using heuristic optimization are studied. For a final "proof" of the found methods with respect to the target audience of the work, circuit designers, also an existing circuit implementation of a broadband SDM with a classic loopfilter architecture will be modified - maximally reusing the existing components - into a single amplifier structure; the circuit will be manufactured and tested as proof of concept.