Circuits for efficient and secure power delivery in distributed applications

167 Pages·2017·22.24 MB·English

Circuits for Efficient and Secure Power Delivery in
Distributed Applications SSACUSETS INSTITUTE
MA OF TECHNOLOGY
by MAR 13 2017
Nachiket Venkappayya Desai
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ARCHNES
B.Tech., Indian Institute of Technology, Kharagpur (2010)
S.M., Massachusetts Institute of Technology (2012)
Submitted to the Department of Electrical Engineering and Computer
Science
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
February 2017
@ Massachusetts Institute of Technology 2017. All rights reserved.
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Signature
A u th o r ..... - -- - - -- - -- - .................
Department of Electrical Engineering and Computer Science
November 8, 2016
Signature redacted
Certified by.........
Anantha P. Chandrakasan
Vannevar Bush Professor of Electrical Engineering and Computer
Science
Thesis Supervisor
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Signature redacted,z
Accepted by .............
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Chair, Department Committee on Graduate Students
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Circuits for Efficient and Secure Power Delivery in
Distributed Applications
by
Nachiket Venkappayya Desai
Submitted to the Department of Electrical Engineering and Computer Science
on November 8, 2016, in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy
Abstract
The growing number of widely distributed IoT devices presents new challenges in
power delivery. Existing frameworks for charging electronic devices, be they wired
or wireless, either end up limiting the amount devices can be shrunk due to the size
of standardized connectors or end up restricting their free placement due to their
reliance on charging mats. The large amounts of vital data IoT devices gather and
their heavily distributed nature also makes it important to protect them against
unauthorized or malicious charging that might be aimed at damaging and/or stealing
data from them. This thesis focuses on developing circuits and architectures to enable
a more distributed and secure approach to charging such devices by exploring two
topics in particular - energy harvesting and wireless charging.
First, a converter for harvesting power from thermoelectric generators (TEGs)
is presented. The converter is capable of cold-starting from a bipolar supply as
low as 40 mV, making it suitable for applications where the direction of heat flow
from which energy is harvested could be bi-directional. Upon cold-starting from
such low voltages, the converter transitions to a high-efficiency mode in steady state
that achieves up to 60% efficiency while delivering 110 pW of power. With the goal
of building a fully integrated transformer in the future, techniques for modeling an
integrated transformer for optimal harvester performance have also been presented.
Second, a receiver for device-to-device wireless charging is presented. The receiver
dynamically measures the end-to-end system efficiency adjusts the ac input impedance
it presents to the wireless power transmission system in order to track the maximum
efficiency point. It also employs an inverter-inspired resonant rectifier that overall
results in a 13.8% total energy saving for the transmitter with when the received
power is 650 mW.
Next, an adaptive rectifier control scheme for wireless power transfer that inte-
grates linear regulation into the high-side switches of the rectifier is presented. This
has the capability to reduce the area of an integrated converter by eliminating an
additional LDO at the output of the rectifier. Additionally, the regulation technique
presented results in lower system efficiency degradation when the output power is
regulated below the maximum value.
Finally, a wireless power receiver detuning technique is presented. Detuning al-
lows the receiver to protect itself from harmful transients imposed by counterfeit or
malicious chargers, by reducing the received power by up to 16 x. It also allows mul-
tiple receivers coupled to the same charger to co-operate in order to balance their
received powers. Using this technique, the asymmetry in the output powers of two
receivers at 4:1 distance ratios from the transmitter can be reversed.
Thesis Supervisor: Anantha P. Chandrakasan
Title: Vannevar Bush Professor of Electrical Engineering and Computer Science
To my mother, Savita, and my father, Venkappayya Desai
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Acknowledgments
It only feels like yesterday when I first set foot on the MIT campus, getting lost
multiple times while going from one Orientation event to the next, and feeling like
grad school was one big party. While that certainly (and fortunately, I might add)
did not turn out to be true, it would be fair to say that this has been the most
exciting period of my life and would probably continue to be so. This is a token
of my appreciation to everyone that has made these past six years such an amazing
journey.
The person I am indebted to the most for making my experience at MIT such
a rewarding one would be my advisor, Prof. Anantha Chandrakasan. Not only has
he been a constant source of inspiration and support to try out new ideas and push
the boundaries of research, but I have learnt so much more from him about topics
that might, at first glance, be considered peripheral to academic life, but play a very
important role in it - things such as logistics, funding and presenting your work
effectively. His propensity for seeking out new ways to solve problems or new ways to
improve things by drawing on ideas from a very diverse set of topics, both in research
and as part of his administrative responsibilities, continues to baffle me. I can only
hope that I am nearly as creative and productive as he is! It has been a great honor
and privilege to be his student.
I would also like to thank Prof. David Perreault and Prof. Jeffrey Lang for
being part of my thesis committee. They have been very supportive throughout the
entire process and have been extremely accommodative with their schedules, both
in scheduling committee meetings and the thesis defense. Their inputs have helped
refine this thesis. I have also been fortunate to have learnt a great deal from both of
them even before they became part of my thesis committee, through some incredibly
well-taught classes on Power Electronics and Electromagnetics.
None of this would have been possible without the financial support that was
provided by Foxconn and the MIT Lincoln Labs. I am indebted in particular to Yihui
Qiu
from Foxconn and Scott Van Broekhoven from Lincoln Labs for the confidence
they placed in us as well as for their inputs during the course of the work.
I have been privileged to have collaborated with some very talented researchers
over these years. I learnt a great deal about circuit design and implementing those
on silicon from Jerald Yoo, who mentored me during my first two years as a Masters
student. More recently, working with Chiraag Juvekar has been an amazing experi-
ence, both in terms of learning so much about the theoretical aspects of cryptography
as well as spending long days and nights in the lab getting our demo to work. The
weekly meetings on the integrated thermal energy harvesting project have been a
great learning experience as well, for which I am thankful to Preetinder Garcha, Dina
El-Damak, Minjie Chen, Mohammad Araghchini, Jorge Troncoso and Prof. Jeffrey
Lang from MIT, and Dennis Buss, Terry Sculley and Joyce Mullenix from Texas In-
struments. The extensive discussions with Ujwal Radhakrishna on vibration energy
harvesting have also been very enlightening.
Fabrication support for the designs to be implemented on silicon has been kindly
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provided by TSMC. I am especially thankful to Michael McIlrath at MIT and Arun
Achyuthan at TSMC for the fantastic work they do in making sure the process runs
smoothly. Chip tapeouts inevitably run late, and I can only imagine how stressful it
must for someone to who, on a regular basis, has to make sure all the designs come
in on time so that they can be put together and sent to the fab.
I am grateful to Texas Instruments for giving me the opportunity to spend two
summers with them as an intern and include the work I did there in this thesis,
and to Dennis Buss for his assistance in setting them up. These internships were an
invaluable learning experience on how research and development is done in industry
and on how projects are conceptualized and evaluated. I would like to thank Yogesh
Ramadass and Gianpaolo Lisi for being such great mentors, making sure I was given
challenging problems to work on and helping get so much work done in such little
time. It was also a pleasure to work closely with Sakshi Arora, Raj Subramonian and
Gerard Socci during my second internship.
A large fraction of my time at MIT was spent in the lab, along with other mem-
bers of Ananthagroup. The atmosphere of friendship and cooperation that Anantha
has fostered and that previous students have cultivated in this group make it an ab-
solute pleasure to be a part of it. Owing to the breadth of the research done in the
group, every whiteboard discussion (that usually lasts hours!) is an amazing learning
experience. I have learnt so much about RF circuits from Arun and Phil, security
from Chiraag and video coding from Mehul and Rahul - topics that I would probably
know very little of otherwise. Saurav was an invaluable resource on different aspects
of power converter design in the early years. Aside from work, the social aspect of the
group is what makes it feel like a second family. I will particularly miss the (almost)
daily group lunch in the lab, the procrastination circles and the various Anantha-
group sports clubs. I wish the next generation of Ananthagroup students the best,
and hope they keep the culture going.
Margaret, our lab admin, is simply fantastic with all the administrative stuff! It
goes without saying that 38-107 functions so smoothly largely due to her diligence in
managing accounts and reimbursements, setting up meetings, etc. I would also like
to thank the EECS and MTL staff, particularly Janet, Alicia and Debb, for being
really supportive over the years. And a special shout-out to the 6.002 Spring 2016
staff and students for making my TA experience so enjoyable.
Outside of work, I have been blessed to have an amazing group of friends. I am
especially thankful to my girlfriend, Tanaya, who has been a constant source of love
and support. The various culinary endeavors undertaken with my roommates, Sagar
and Arun (who did most of the work), will be sorely missed. So will the various
weekend hikes, skiing trips with Sivaraman and Vishnu and general hangout sessions
with Atulya, Chiraag, Harshad, Mehul, Sai, Sameer, Sayalee, Tapovan, Ujwal, and
others. My experiences with taking up Squash and long-distance running during my
time here were a lot of fun because of the company of some great folks. It has also
been a pleasure being a part of AID-MIT and seeing it grow so much in such little
time, in no part due to the tireless efforts of some very dedicated volunteers. I hope
it continues to grow in the future.
Last, but not the least, I would like to express my sincerest gratitude to my
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parents, for their love, support and encouragement to follow my dreams. Throughout
my life, they have done their best to make sure I never lacked for anything and have
made countless sacrifices in the process. This thesis is dedicated to them.
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