MICL Seminar

Successive Approximation and Time Interleaving for Sub-90nm CMOS ADCs

Rick Carley

Carnegie Mellon University
Thursday, April 11, 2013
3:00pm - 5:00pm
3316 EECS

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About the Event

In the early days of MOS integrated circuits (way back in the 1970's), getting any kind of accurate analog-to-digital converter (ADC) to work was very challenging. Designers only had depletion-mode and enhancement-mode NMOS transistors to work with; and, getting even modest analog voltage gain was quite difficult. The successive approximation ADC, which does not require an amplifier (just a comparator), took off as a dominant ADC architecture in those early days of MOS. Then, as CMOS took hold in the 1980's, many other ADC architectures took over and successive approximation became just one of many possible choices. As CMOS process technology scales below gate lengths of 90nm, achieving analog voltage gain is again becoming a major challenge. In part, the more three dimensional nature of a very short channel MOSFET results in drain induced barrier lowering that typically drops the maximum gain of a single transistor amplifier down into the 5-10X range. Further, because the power supply voltages have dropped down to 1V or below, adding cascode transistors to increase voltage gain is also difficult. In this talk, the successive approximation ADC architecture will be reviewed. Two very different 45nm CMOS ADC designs that were recently developed at Carnegie Mellon will be described. The first ADC adopts digital error correction techniques to increase the accuracy of the basic successive approximation ADC to over 11 bits. The second ADC to be described develops strategies for achieving extremely high sampling rates (over 2GS/s) using time interleaving of successive approximation ADCs. The conclusion of this talk is that the characteristics of deeply scaled CMOS technologies have caused a re-emergence of the popularity of successive approximation ADCs.


L. Richard Carley received an S.B. in 1976, an M.S. in 1978, and a Ph.D. in 1984, all from the Massachusetts Institute of Technology. He joined Carnegie Mellon University in Pittsburgh Pennsylvania in 1984, and in March 2001, he became the STMicroelectronics Professor of Engineering at CMU. Dr. Carley’s research interests include design, modeling and analysis of hardware and algorithms related to data communications networks, human/cyber networks, and data storage devices. The technologies he applies to these systems include analog and RF integrated circuit design in deeply scaled CMOS technologies and novel nano-electro-mechanical device design and fabrication. Dr. Carley has been granted 15 patents, authored or co-authored over 120 technical papers, and authored or co-authored over 20 books and/or book chapters. He has won numerous awards including Best Technical Paper Awards at both the 1987 and the 2002 Design Automation Conference (DAC). In 1997, Dr. Carley co-founded the analog electronic design automation startup Neolinear which was acquired by Cadence in 2004.

Additional Information

Contact: Fran Doman

Phone: 734-615-3499


Sponsor(s): MICL and Texas Instruments

Open to: Public