On A/D Converters with Low-Precision Analog Circuits and Digital Post-Correction

155 Pages·2013·2.25 MB·English

by  Jonas Biveroni

ETH Library
On A/D converters with low-
precision analog circuits and digital
post-correction
Doctoral Thesis
Author(s):
Biveroni, Jonas
Publication date:
2013
Permanent link:
https://doi.org/10.3929/ethz-a-007635276
Rights / license:
In Copyright - Non-Commercial Use Permitted
Originally published in:
Series in Signal and Information Processing 24
This page was generated automatically upon download from the ETH Zurich Research Collection.
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Series in
Diss. ETH No. 20629
Signal and
Information
Processing
On A/D Converters
Volume 24
with Low-Precision
Analog Circuits and
Digital Post-Correction
A dissertation submitted to
ETH Zurich
for the degree of
Doctor of Sciences
presented by
Jonas Biveroni
MSc ETH in Electrical Engineering and Information Technology
born on March 25, 1977
citizen of Bever (GR) and Samedan (GR)
accepted on the recommendation of
Hartung
Prof. Dr. Hans-Andrea Loeliger, examiner
Gorre Prof. Dr. Boris Murmann, co-examiner
Konstanz
2012
Series in Signal and Information Processing Vol. 24

Editor: Hans-Andrea Loeliger

Bibliographic Information published by Die Deutsche Nationalbibliothek

Die Deutsche Nationalbibliothek lists this publication in the Deutsche
Nationalbibliografie; detailed bibliographic data is available in the internet at http://dnb.d-nb.de.

Copyright © 2013 by Jonas Biveroni

First Edition 2013

HARTUNG-GORRE VERLAG KONSTANZ

ISSN 1616-671X
ISBN-10: 3-86628-452-7
ISBN-13: 978-3-86628-452-4
to Hina ♥

Acknowledgments
First of all, “thank you!” to my PhD supervisor Andi Loeliger for giving
me the opportunity to do research. At the Signal and Information Pro-
cessing Lab (ISI), I found a very inspiring and open-minded environment.
IverymuchappreciateAndi’swayofmakingresearchhappenwhilekeep-
inganotherfocusoneducation. Hiscatchingenthusiasmwasalwaysmost
inspiring and encouraging to me, especially during exhausting periods.
I would also like to thank Prof. Boris Murmann for kindly accepting
to be co-examiner at my PhD examination. Due to his vast knowledge
in real-world circuit design, his valuable comments on my thesis served
as a reality check. Thank you again!
Many thanks also to the professors Amos Lapidoth and Hanspeter
Schmid for the entertaining chats and the great teaching! I am also
grateful for the collaboration with Nikolai Nefedov at the beginning of
my PhD.
I very much enjoyed the Fachsimpeln about electronics with Paddy
Strebel and also Thomas Sch¨arer. Paddy helped me a lot with the chip
testing. I would also like to thank Rita Hildebrand and Marion Widmer
fromtheadministrativestaff. Withyourfreshandcordialkind, youhave
contributed a lot to the ISI spirit!
Most important for my time at the lab: My numerous colleagues
duringall the ISIyears—MatthiasFrey, TobiasKoch, St´ephaneTinguely,
Mich`ele Wigger, Maja Ostojic, Justin Dauwels, Volker Koch, Sascha
Korl, Junli Hu, Stefan Moser, Daniel H¨osli, Natalia Miliou, Murthy
Devarakonda, Christoph Reller, Raphael Berner, Ligong Wang, Georg
Wilckens, Lukas Bolliger, Mehdi Molkaraie, Jiun-Hung Yu, Lukas Brud-
erer, Christoph Bunte, Sarah Neff, Christian Schu¨rch—Thank you all!
Many thanks also to my colleagues from the Integrated Systems Lab
(IIS), Frank Gu¨rkaynak, Craig Keogh and especially Ju¨rg Treichler for
the great support in chip design.
v
vi Acknowledgments
Ofcourse,thisthesiswouldnothavebeenpossiblewithoutthesupport
of my friends, especially Andrea, Uli, Miri, Andreas. I am also deeply
grateful for the love and support of my parents and brothers.
But most important—Thank you, Hina and Hannah, for all.
Abstract
Progress in the fabrication of integrated circuits (ICs) enables smaller
and smaller minimum feature sizes, so that more and more transistors
can be realized per chip area. Digital circuits greatly benefit from the
miniaturization. Bycontrast,analogcircuitssufferfromreducedprecision
when component sizes are decreased, because for decreased component
sizes, the respective component values increasingly deviate from their
nominal values in a non-deterministic manner. Some of the resulting
precisionerrorscanbecorrectedbydigitalprocessing. Thus, apromising
approachtomixed-signalcircuitdesignisusingsmalllow-precisionanalog
circuits and applying digital correction, such that the system as a whole
is sufficiently precise.
In this thesis, we apply the above-mentioned approach to analog-to-
digital converters (ADCs), as they combine analog and digital circuits.
ADCs are key building blocks of modern electronic devices which process
physical quantities digitally. Examples of such devices are mobile phones,
digital cameras or measurement devices such as digital voltmeters. Such
devices often contain several ADCs which convert radio signals, touch-
screen information, optical image data or plain voltage values into digital
signals.
Specifically, we consider ADCs using low-precision analog circuits
and digital post-correction. We mostly consider static characteristics,
ignoring dynamical issues like noise, sampling or settling. The thesis
presents a few studies and ideas on the topic.
We study the static accuracy of various flash-type ADCs with low-
precision components and digital correction. We model the key analog
componentsandassessthestaticaccuracyusingMonteCarlosimulations.
Similarly, we extend the discussion of the static accuracy to sequential
ADCs based on beta expansions (“radix <2” conversion). We conclude
that both flash-type ADCs and sequential ADCs using low-precision
vii
viii Abstract
analog circuits are useful with proper digital correction.
Afterfabrication, thestaticcharacteristicsoftheADC’slow-precision
analog part are not known exactly. However, proper digital correction
requires the static characteristics to be known. We thus elaborate a
calibration method, which is suited for a built-in self-test (BIST). The
method includes a test signal generator circuit and algorithms which
estimate the static characteristics using measurement data of the test
signals. The algorithms are based on Gaussian message passing on a
graphical model (factor graph) of the system. In simulations, we achieve
very accurate estimations of the static characteristics using the presented
method.
Finally, we design and manufacture an experimental pipeline ADC
in a 0.13µm CMOS process. The circuit implements the beta-expansion
principle using simple analog low-precision sub-circuits.
Keywords: Analog-to-digital converter, flash ADC, sequential ADC,
low-precision analog circuits, digital post-correction, static accuracy,
calibration, factor graph, message-passing algorithms, integrated circuit
design.
Kurzfassung
Fortschritte in der Fertigung von integrierten Schaltungen erm¨oglichen
immer kleinere Strukturen, so dass immer mehr Transistoren auf gleicher
Fl¨ache Platz haben. Digitale Schaltungen profitieren stark von dieser
Miniaturisierung. Analoge Schaltungen hingegen werden zunehmend un-
pr¨azise, je kleiner die Komponenten sind, denn je kleiner die Komponen-
ten, desto st¨arker weichen deren Werte auf nichtdeterministische Weise
vom jeweiligen Nennwert ab. Einige der entstehenden Ungenauigkeiten
k¨onnen korrigiert werden mit digitaler Nachbearbeitung. Ein vielverspre-
chenderAnsatzimEntwurfvonMixed-Signal-Schaltungenistdeshalbdie
Verwendung von kleinen, unpr¨azisen analogen Schaltungen mit digitaler
Fehlerkorrektur, so dass das Gesamtsystem wiederum pr¨azise genug ist.
In dieser Arbeit wenden wir den obengenannten Ansatz auf Analog-
Digital (A/D)-Wandler an, da diese analoge und digitale Schaltungen
zusammenbringen.A/D-WandlersindzentraleBauelementevonheutigen
elektronischen Ger¨aten, welche physikalische Gr¨ossen digital verarbei-
ten. Beispiele solcher Ger¨ate sind Mobiltelephone, Digitalkameras oder
Messger¨ate wie z.B. digitale Voltmeter. Solche Ger¨ate enthalten oft meh-
rere A/D-Wandler, welche Funksignale, Touchscreen-Daten, optische
Bilddaten oder einfach Spannungswerte in digitale Signale umwandeln.
Wir befassen uns mit A/D-Wandlern mit unpr¨azisem Analogteil und
digitaler Fehlerkorrektur. Haupts¨achlich betrachten wir deren statische
Eigenschaften und ignorieren dynamische Vorg¨ange wie Rauschen, Ab-
tastung oder Einschwingvorg¨ange. In dieser Dissertation stellen wir ein
paar Studien und Ideen zum Thema vor.
WiruntersuchendiestatischenEigenschaftenvonverschiedenenFlash-
¨ahnlichen A/D-Wandlern mit unpr¨azisen Komponenten und digitaler
Fehlerkorrektur. Dazu modellieren wir die wichtigen analogen Kompo-
nenten und ermitteln die statische Genauigkeit der Wandler anhand
von Monte-Carlo-Simulationen. Entsprechend dazu untersuchen wir se-
ix