*OSU EECS will be hosting Dr. Nguyen T. Thao this Friday at 11am in Weniger Hall 116. There will be no colloquium this Thursday.
Upcoming colloquiums are posted at http://eecs.oregonstate.edu/graduate/colloquium/ Friday February 4 11:00 - 11:50 AM Weniger 116 Nguyen T. Thao Associate Professor Electrical Engineering City University of New York Breaking the nonlinear feedback loop of Sigma-Delta modulators Sigma-Delta modulation is the modern technique to perform high resolution analog-to-digital conversion. A Sigma-Delta modulator (SDM) consists of a feedback system that coarsely quantizes an oversampled analog signal. From a signal processing point of view, an SDM is a system of high simplicity, but paradoxically of difficult rigorous analysis. Due to the presence of a nonlinear operation (quantization) in the feedback loop, one is not able to derive the explicit expression of the output of an SDM in time. With the classic white-noise assumption of the quantizer error, one "linearizes" the quantization operation, and thus facilitates the analysis, but one only obtains partial information on the error signal with limited validity. A genuine explicit expression of the output is necessary to study refine properties of the error such as correlation with the input, idle tones, etc... In this talk, we show for a generic family of Nth order SDM's (among other conditions, the N zeros of the noise transfer function must be located at z=1) with constant inputs, that the system is mathematically equivalent to a linear feedback system, followed by an N-dimensional nonlinear but instantaneous operation. In other words, the nonlinear mechanisms of the SDM can be mathematically extracted from the feedback loop for signal analysis. The explicit derivation of the equivalent instantaneous nonlinear operation is still difficult, but its existence is mathematically proved, and an approximate knowledge of this function is already sufficient to derive error properties of SDM's not predictable by white-noise modeling. We finally explain how this theory can be extended to time-varying inputs. Biography Nguyen T. Thao received his Ph.D. degree in Electrical Engineering from Columbia University, New York, in 1993. He is currently an Associate Professor in the Department of Electrical Engineering of the City University of New York. His current research emphasis is the theoretical signal analysis of Sigma-Delta modulation. _______________________________________________ Colloquium mailing list [email protected] https://secure.engr.oregonstate.edu/mailman/listinfo/colloquium
