Full-Custom Analog/Mixed Signal Components for CMOS Integrated Autonomous Microelectronic ...

188 Pages·2014·8.08 MB·English

by  Matthias Kuhl

Dissertation zur Erlangung des Doktorgrades der
Technischen Fakultät der
Albert-Ludwigs-Universität Freiburg im Breisgau
Full-Custom
Analog/Mixed Signal Components
for CMOS Integrated Autonomous
Microelectronic Systems
M. Sc. Matthias Kuhl
02.06.2014
Albert-Ludwigs-Universität Freiburg im Breisgau
Technische Fakultät
Fritz-Hüttinger-Professur für Mikroelektronik
Dekan
Prof. Dr.-Ing. Yiannos Manoli
Referenten
Prof. Dr.-Ing. Yiannos Manoli
Prof. Dr.-Ing. Roland Thewes
Datum der Disputation
16.12.2013
"Genius is one per cent inspiration,
ninety-nine per cent perspiration."
(Thomas Alva Edison)

Contents
Abstract 1
Zusammenfassung 3
1 Introduction 5
1.1 Defining Autarky, Autonomy, and Heteronomy . . . . . . . . . . . . . 6
1.2 General Topology of Autonomous Microelectronic Systems . . . . . . 7
1.3 Sample Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.1 I2Brenn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3.2 Smart Bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4 Author’s Contribution & Thesis’s Organization . . . . . . . . . . . . 15
2 Input Units 17
2.1 Overview of Available Input Units . . . . . . . . . . . . . . . . . . . . 17
2.2 Stress Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.1 Sensor Principle & Sensor Design . . . . . . . . . . . . . . . . 19
2.2.2 Sensor Operation Mode - Discrete Current Switching . . . . . 21
2.2.3 Stress Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2.4 Sensor Layout & Offset Voltage . . . . . . . . . . . . . . . . . 23
2.2.5 Noise Characterization . . . . . . . . . . . . . . . . . . . . . . 25
2.2.6 Common Mode Prediction and Manipulation . . . . . . . . . . 28
2.3 Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3.1 Fuel Cell Principle & Fuel Cell Design . . . . . . . . . . . . . 33
2.3.2 Fuel Cell Connectivity in CMOS . . . . . . . . . . . . . . . . 34
2.3.3 Electrical Parameters of the Fuel Cells . . . . . . . . . . . . . 35
2.4 Planar Microcoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3 Processing Units 39
3.1 Overview of Available Processing Units . . . . . . . . . . . . . . . . . 39
3.2 Reference Circuits - Amplitude Related . . . . . . . . . . . . . . . . . 41
3.2.1 Shunt Voltage Regulator . . . . . . . . . . . . . . . . . . . . . 42
3.2.2 Bandgap Current & Voltage Source . . . . . . . . . . . . . . 45
3.3 Reference Circuits - Timing Related . . . . . . . . . . . . . . . . . . . 48
3.3.1 Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.3.2 Clock Extractor . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.3.3 Frequency Divider . . . . . . . . . . . . . . . . . . . . . . . . 58
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Contents
3.4 Fuel Cell Bypass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.5 Differential Difference Amplifier (DDA) - Sensor Interface . . . . . . . 61
3.5.1 Basics of Instrumentation Amplifiers . . . . . . . . . . . . . . 62
3.5.2 Basics of DDAs . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3.5.3 DDA Feedback Configuration . . . . . . . . . . . . . . . . . . 65
3.5.4 Design & Layout of the DDA . . . . . . . . . . . . . . . . . . 67
3.5.5 Digital Back-End with Automatic Gain Adjustment . . . . . . 92
3.5.6 DDA Measurement Results . . . . . . . . . . . . . . . . . . . 94
3.5.7 DDA Improvements . . . . . . . . . . . . . . . . . . . . . . . . 100
4 Output Units 101
4.1 Low-Dropout Voltage Regulator (LDO) - DC Voltage Converter . . . 101
4.1.1 Basics of LDOs . . . . . . . . . . . . . . . . . . . . . . . . . . 102
4.1.2 Parallel Low-Dropout Voltage Regulator (PLDO) . . . . . . . 104
4.1.3 Switched Low-Dropout Voltage Regulator (SLDO) . . . . . . . 108
4.1.4 Multi-Purpose Low-Dropout Voltage Regulator (MLDO) . . . 111
4.2 Rectifier - AC Voltage Converter . . . . . . . . . . . . . . . . . . . . 118
4.3 Radio Frequency Communication . . . . . . . . . . . . . . . . . . . . 120
4.3.1 RF Transmitter - Energy Transmission . . . . . . . . . . . . . 120
4.3.2 Back-Telemetry - Data Transmission . . . . . . . . . . . . . . 122
4.3.3 RF Demodulator - Data Transmission . . . . . . . . . . . . . 122
5 Sample Projects 125
5.1 I2Brenn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
5.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
5.1.2 Fabrication Technology . . . . . . . . . . . . . . . . . . . . . . 126
5.1.3 ibre0201 Design Overview . . . . . . . . . . . . . . . . . . . . 127
5.1.4 ibre0201 Characterization . . . . . . . . . . . . . . . . . . . . 129
5.1.5 ibre0201 Conclusion & ibre0301 Modifications . . . . . . . . . 132
5.1.6 ibre0301 Fuel Cell Switching . . . . . . . . . . . . . . . . . . . 133
5.2 Smart Bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
5.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
5.2.2 Smart Bracket Overview . . . . . . . . . . . . . . . . . . . . . 139
5.2.3 System Components . . . . . . . . . . . . . . . . . . . . . . . 141
5.2.4 System Characterization . . . . . . . . . . . . . . . . . . . . . 145
6 Conclusion & Outlook 149
6.1 I2Brenn Conclusion & Outlook . . . . . . . . . . . . . . . . . . . . . . 149
6.2 Smart Bracket Conclusion & Outlook . . . . . . . . . . . . . . . . . . 151
6.3 Benefits for Upcoming Projects . . . . . . . . . . . . . . . . . . . . . 153
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Contents
Acknowledgments 155
A Appendix 157
A.1 Author’s Scientific Track . . . . . . . . . . . . . . . . . . . . . . . . . 157
A.2 Supervised and Co-Supervised Theses . . . . . . . . . . . . . . . . . 161
Bibliography 163
Nomenclature 175
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Abstract
This thesis summarizes the author’s research activities on the development of au-
tonomousmicroelectronicsystems,whichcombineelectro-chemicalorelectro-mecha-
nical devices with the processing power of modern CMOS technologies within one
chip. Termed by the keyphrase “More-than-Moore”, such extensions of CMOS pro-
cesses allow for the construction of fully integrated microsystems, leading to ex-
tremely compact autonomous microsensor nodes.
The project I2Brenn introduces CMOS-integrated fuel cells and thus describes an
energy-autonomous microsystem. The project Smart Bracket presents the integra-
tion of stress sensors and thereby lays the foundation for a telemetric stress mapping
system integrable into orthodontic brackets. Developing these autonomous micro-
electronic systems and designing the required components are the central objectives
of this thesis. Even though all circuit components were developed as application
specific blocks, the resulting architectures and discussed concepts as well as the the-
oretical and practical results are universally valid. For this reason, the developed
full-custom analog/mixed-signal CMOS circuits are presented as collections of in-
put,processing,andoutputunits,thusfollowingtheterminologyofsignalprocessing
chains.
Input Units Three devices were developed within or in parallel to this thesis, en-
abling a microsystem to gather information from its environment: electro-magnetic
microcoils, electro-mechanical stress sensors, and electro-chemical fuel cells. The re-
quired performance of microcoils for autonomous microelectronic systems was speci-
fied, and the fabricated prototypes were characterized electrically. The initial design
of the stress sensors was supplemented by the development of an additional design
parameter, thus offering an adaptation of the operating conditions. The impact of
the CMOS integrated fuel cells on standard circuitry was analyzed, and layout rules
were proposed. Furthermore, a variable formation of these cells was generated using
CMOS switches, resulting in adaptive fuel cell cascades for a use-oriented balance
between performance and efficiency.
Processing Units A differential difference amplifier was implemented as analog
readout frontend for stress sensors. It utilizes an amplitude related gain selection to
actively regulate the total harmonic distortion to less than 2%, and a current injec-
tion path to improve the power supply rejection ratio by up to 37 dB. Furthermore,
a control unit for the experimental fuel cells was developed in order to perform
a functionality check on each cell. This inspection guarantees reliable operation,
while consuming only 30 pWs. Processing chains are in urgent need of appropri-
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ate reference elements for reliable quantitative comparisons. Therefore, two shunt
voltage references were developed and combined to a voltage regulator, limiting an
unregulated input voltage to a maximum value of 3.3 V, while consuming 900 µA
during startup and 4 µA in steady state. A complementary-to-absolute-temperature
current and voltage reference was combined with a current-starved ring oscillator,
which together generate a temperature-compensated clock signal of 35 kHz with a
power consumption of only 620 nW. Additional timing-related processing units, i.e.,
a clock extractor and clock dividers, were developed.
Output Units The quality of the supply voltage is of high importance for the
overall system performance. Three concepts of low-dropout voltage regulators were
developed: the first allows for parallel connection of various DC sources, the second
increasespowerefficiencyincontrasttothefirstbyupto50%byusingsourceswitch-
ing, and the third offers multiple user-selectable output voltages between 1.1 V and
3.3 V. Additionally, two rectifiers were compared, namely a full-wave rectifier and
a negative voltage converter with attached Schottky diode. The latter reduces the
voltage drop by a factor of 3.5 in comparison to the full-wave rectifier. As examples
of information-related output units, a back-telemetry communication concept and
a radio frequency demodulator were developed, both operating at 13.56 MHz.
Based on all these components, the energy-autonomous system I2Brenn and the
stress mapping system Smart Bracket were developed and fabricated. Subsequently,
thefullyfunctionalprototypeswerecharacterized. Inconclusion, thecombinationof
electro-chemical or electro-mechanical devices with the processing power of modern
CMOS technologies culminated in extremely compact autonomous microelectronic
systems.
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