Comparator design and analysis for comparator-based switched-capacitor circuits

The design of high gain, wide dynamic range op-amps for switched-capacitor circuits has become increasingly challenging with the migration of designs to scaled CMOS technologies. The reduced power supply voltages and the low intrinsic device gain in scaled technologies offset some of the benefits of the reduced device parasitics. An alternative comparator-based switched-capacitor circuit (CBSC) technique that eliminates the need for high gain op-amps in the signal path is proposed. The CBSC technique applies to switched-capacitor circuits in general and is compatible with most known architectures. A prototype 1.5 b/stage pipeline ADC implemented in a 0.18 Fým CMOS process is presented that operates at 7.9 MHz, achieves 8.6 effective bits of accuracy, and consumes 2.5 mW of power. Techniques for the noise analysis of comparator-based systems are presented. Nonstationary noise analysis techniques are applied to circuit analysis problems for white noise sources in a framework consistent with the more familiar wide-sense-stationary techniques. The design of a low-noise threshold detection comparator using a preamplifier is discussed. Assuming the preamplifier output is reset between decisions, it is shown that. for a given noise and speed requirement, a band-limiting preamplifier is the lowest power implementation. Noise analysis techniques are applied to the prototype CBSC gain stage to arrive at, a theoretical noise power spectral density (PSD) estimate for the prototype pipeline ADC. Theoretical predictions and measured results of the input referred noise PSD for the prototype are compared showing that the noise contribution of the preamplifier dominates the overall noise performance. Thesis Supervisor: Hae-Seung Lee Title: Professor of Electrical Engineering Thesis Supervisor: Charles G. Sodini Title: Professor of Electrical Engineering Acknowledgments First, I would like to thank my wife Carrie for her patience and understanding. Without her support, I would not have made it. I realize it was not easy having a graduate student for a husband for 6 years. I look forward to our life after graduation. I would, like to thank my research advisors and mentors Prof. Harry Lee and Prof. Charlie Sodini. Their guidance and instruction during my years at MIT made my graduate career challenging, exciting and rewarding. I am indebted to them for their time, patience, and support. I would also like to thank John Fiorenza for listening to me talk about noise for the last 6 years. It has been nice to have at least one person in the office who had some idea of what I was talking about and that I could bounce ideas off of. And in our spare time, I think we may have actually solved some of the worlds problems over coffee. I would like to thank Peter Holloway for his assistance, guidance and many stimulating discussions over the last couple of years of my Ph.D, and Prof. Jim Roberge for taking the time to read my thesis and be on my committee. I would. like to acknowledge the many members of the Sodini group during my tenure at MIT. The group who endured the Ph.D. program with me: Anh Pham, Andy Wang, Lunal Khuon, and Albert Jerng. The many good technical discussions, the dinners out, the homework, the tapeouts, and finally graduation. To the many junior members of the group, some who have come and gone and others who must still carry on: Kevin Ryu, Farinaz Edalat, Nir Matalon, Kartik Lamba, Khoa Nguyen, Ivan Nausieda, Albert Lin, Jit Ken Tan, Matt Powell and Johnna Powell: it has been a pleasure to work with all of you. I also cannot forget to mention those who were senior members when I arrived: Don Hitko, Dan McMahill, Ginger Wang, Iliana Fujimori Chen, and Pablo Acosta Serafini for helping me when I was new. Similarly, I would like to acknowledge the members of the H. S. Lee group: former cube-mate Mark Peng, contemporaries Andrew Chen, Matt Guyton, Albert Chow, fellow Big Ten alum Mark Spaeth for many great technical and non-technical conversations, Lane Brooks for many helpful discussions about CBSC, and the senior members who welcomed me to the group on their way out: Kush Gulati, Ayman Shabra, and Susan Luschas. I have also had the pleasure of meeting many other outstanding individuals during my time at MIT who are to numerous to name, including my colleagues in the MTL community and the students on the second floor of Bldg 38. I would like to acknowledge the MTL Mallards Hockey Team and especially Andy Fan for his efforts to keep the team going and his inspirational pregame emails. Hockey with the Mallards was an important part of my MIT education. I would like thank the administrative assistants Kathy Patenaude, Rhonda Maynard, and Carolyn Collins who always helped to part the MIT red tape. Marilyn Pierce, who has been of great assistance in all departmental and institute matters. She is always looking out for the graduate students. Debb Hodges-Pabon, her enthusiasm is contagious; she has made the MTL a great place to work. I would like to thank the MTL computer and CAD support staff: Mike Hobbs, Bill Maloney, and Mike McIlrath for keeping the computing and CAD infrastructure functioning. I would like to thank my parents for their continued support and encouragement. I would like to thank my brother Scott for letting me vent my frustrations when necessary; it is great to have someone else in the family who really understands the life of a doctoral candidate. The author was funded by the MARCO Focus Center for Circuits and System Solutions (C2S2, www.c2s2.org) contract 2003-CT-888x and the MIT Center for Integrated Circuits and Systems (CICS). The chip fabrication and packing for the prototype in this thesis were donated by National Semiconductor. Dedication I dedicate this thesis to my Grandmother Beulah T. Fleming (January 6, 1912August 11. 2006) who passed away during my final days at MIT. Her letters and phone calls were always a welcome respite from life as a graduate student. I could always count on her being awake at all hours of the night, eager to hear about recent events in my life, and willing to share her thoughts on current events or memories of days gone by.