The Re-Emergence of Successive Approximation as the Architecture of Choice for Integrated Analog to Digital Converters

SpeakerL. Richard Carley
Organization Carnegie Mellon University
LocationMonteith Research Center (MRC) 136
DateMarch 29, 2010 3:00 PM

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 of any kind, took off as a dominant ADC architecture in the 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 to gate lengths of 45nm and below, 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 gain of a single transistor amplifier down into the 5-10X  range.  Further, because the power supply voltages have dropped down under 1V,  adding cascode transistors to increase voltage gain is 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 will drive a re-emergence of the successive approximation ADC as the architecture of choice for implementations in those technologies.

Biography
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 analog/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 as sold to Cadence in 2004.

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