This paper presents a new approach for estimating non-idealities in unit element feedback digital-to-analog converters of Sigma-Delta analog-to-digital converters. The presented method involves a background correlation technique to determine static and dynamic device mismatches causing linear time-invariant errors of the unit cells, as well as a way to digitally correct a modulator's output. Simulations show that the method can be used to precisely estimate imperfections and improve non-ideal modulators up to their ideal resolution, independent from the chosen oversampling ratio or architecture. The method is defined mathematically and verified by simulations. Comparisons with a common dynamic element matching technique show its superior behavior especially for low oversampling ratios.