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
  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Electrical and Computer Engineering
  • Specialization
    • Biomedical Engineering
  • Supervisor / co-supervisor and their department(s)
    • Elliott, Duncan (Electrical and Computer Engineering)
    • Moez, Kambiz (Electrical and Computer Engineering)
  • Examining committee members and their departments
    • Barlage, Doug (Electrical and Computer Engineering)
    • Nairn, David (University of Waterloo, Electrical and Computer Engineering)
    • Mousavi, Pedram (Mechanical Engineering)