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

• Author / Creator

  Davis, Caitlin

• 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.

• Subjects / Keywords

  • IOP
  • Low-power
  • VLSI
  • Capacitive-to-digital-conversion
  • Low-voltage
  • Switched-capacitor

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3HQ2H

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.