An H∞ Approach for Robust Calibration of Cascaded Sigma Delta Modulators

In this paper, we propose a novel robust H_∞ optimisation approach to the design of digital filters for calibrating 2-1 cascaded sigma delta modulators. The main contribution of this paper consists of two parts. First, we develop a new filter design technique based on a linear matrix inequality (LMI) approach to model-matching problem with polytopic uncertainties in parameters. The advantage of the proposed method is that it leads to an optimal, less conservative, solution to the robust H_∞ filtering problem. The second contribution involves the application of the proposed robust filter design scheme to correct for inevitable and unwelcome analog imperfections typically associated with cascaded sigma delta modulators. For numerical illustration we concentrate on the 2-1 architecture. Simulation results for a range of parameter excursions suggest that our robust H_∞ filter guarantees an improved signal-to-noise ratio (SNR) performance over the nominal filter