Oversampling Analog-to-Digital Conversion

November 30, 2007
Bruce Wooley, Electrical Engineering - Integrated Circuits Laboratory, Stanford University, California

Through the exchange of resolution in time for that in amplitude, oversampling methods can be used to facilitate the realization of programmable high-resolution analog-to-digital converters in scaled CMOS VLSI technologies. So-called oversampling modulators combine coarse quantization at sampling rates well above the Nyquist rate with feedback and subsequent digital filtering to avoid the need for precision analog circuits. Such modulators were originally conceived in the mid-twentieth century as a means of digitizing the rate of change of a signal, rather than the signal itself. However, noise-shaping modulators that directly encode the signal proved to be a more robust approach and have subsequently come into widespread use. In particular, cascades of inherently stable noise shaping modulators are an effective approach to extending the dynamic range of oversampling converters that is largely immune to both analog circuit imperfections and fundamental stability concerns. This presentation begins with an overview of both architectural and circuit issues that attend the design of oversampling modulators, and then presents some recent examples of their implementation under increasingly severe constraints on power dissipation and supply voltage.

Bruce A. Wooley is the Robert L. and Audrey S. Hancock Professor of Engineering and the Chairman of the Department of Electrical Engineering at Stanford University. He received the B.S., M.S. and Ph.D. degrees in Electrical Engineering from the University of California, Berkeley in 1966, 1968 and 1970, respectively. From 1970 to 1984 he was a member of the research staff at Bell Laboratories in Holmdel, NJ, and he joined the faculty at Stanford in 1984. At Stanford he has also served as the Senior Associate Dean of Engineering and the Director of the Integrated Circuits Laboratory. His research is in the field of integrated circuit design, where his interests include low-power mixed-signal circuit design, oversampling A/D and D/A conversion, circuit design techniques for video and image data acquisition, high-speed embedded memory, noise in mixed-signal integrated circuits, and circuits for wireless and wire line communications. Prof. Wooley is a Fellow of the IEEE and the Past President of the IEEE Solid-State Circuits Society. He has served as the Editor of the IEEE Journal of Solid-State Circuits and as the Chairman of both the International Solid-State Circuits Conference (ISSCC) and the Symposium on VLSI Circuits. Among the awards he has received are the University Medal from the University of California Berkeley, the IEEE Journal of Solid-State Circuits 2002 Best Paper Award, recognition for his Outstanding Contributions to the Technical Papers of the International Solid-State Circuits Conference, an IEEE Third Millennium Medal, the Outstanding Alumnus Award from the EECS Department at the University of California, Berkeley, and the IEEE Solid-State Circuits Technical Field Award.