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Permanent link (DOI): https://doi.org/10.7939/R3HQ2H

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A Low-voltage, Low-power Intraocular Pressure Measurement Instrument Open Access

Descriptions

Other title
Subject/Keyword
switched-capacitor
capacitive-to-digital-conversion
low-power
IOP
VLSI
low-voltage
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Davis, Caitlin
Supervisor and department
Moez, Kambiz (Electrical and Computer Engineering)
Elliott, Duncan (Electrical and Computer Engineering)
Examining committee member and department
Mousavi, Pedram (Mechanical Engineering)
Nairn, David (University of Waterloo, Electrical and Computer Engineering)
Barlage, Doug (Electrical and Computer Engineering)
Department
Department of Electrical and Computer Engineering
Specialization
Biomedical Engineering
Date accepted
2014-01-24T08:41:33Z
Graduation date
2014-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Wireless sensing of abnormal intraocular pressure (IOP) levels associated with Glaucoma, a leading cause of blindness, was first proposed in the late 1960’s. While much research has been applied in the intervening time, a suitable commercially available wireless IOP monitoring instrument remains unavailable. The primary difficulty in developing a wireless IOP instrument is reduction of instrument size and power requirements. For implantation, the instrument is desired to be on the order of a few square millimeters. With such a small instrument, achieving biocompatible operation during electromagnetic field exposure necessary for inductively transferred wireless-power requires very low-power, low-voltage operation. This research presents a 325 mV, sub-μW capacitive-to-digital converter with power levels suitable for near-field wireless power operation with using an integrated circuit coil. This low-voltage, low-power operation creates the opportunity for a monolithic, millimeter-scale IOP monitoring instrument using integrated circuit technologies. The designed capacitive sensing circuitry uses Σ∆ modulation to perform capacitance-to-digital conversion. The modulator is implemented with fully-differential switched-capacitor circuits. Operational transconductance amplifiers required for the modulation are implemented with subthreshold inverters. Experimental test- ing shows the prototype instrument, comprised of the designed modulator and commercial capacitive pressure sensors, is capable of resolving 2.1 mmHg while operating at 325 mV using only 30 nW. In comparison with other systems in the field of IOP monitoring, this work represents the lowest operating voltage and power consumption reported to date.
Language
English
DOI
doi:10.7939/R3HQ2H
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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