Title:
Design of a Current-to-Digital Converter for Luminescent Sensing Applied to Transcutaneous Carbon Dioxide Monitoring
Abstract:
Continuous monitoring of arterial carbon dioxide is essential for assessing respiratory function and identifying ventilation deficiencies, yet current clinical practice relies on arterial blood gas analysis, an invasive technique that provides only intermittent measurements in controlled settings. Although transcutaneous carbon dioxide sensing offers a noninvasive alternative by measuring carbon dioxide diffusing through the skin, conventional systems depend on bulky bedside monitors and heating elements, limiting their use to intensive care environments rather than everyday contexts. At the same time, wearable health technologies are increasingly expected to collect critical physiological data unobtrusively and continuously, avoiding disruptions such as repeated blood sampling. Recent advances in luminescence‑based sensing provide a promising foundation for transforming transcutaneous carbon dioxide monitoring from a stationary clinical procedure into a miniaturized, low‑power technology.
This work presents the development and evaluation of several noninvasive, miniaturized sensing platforms that employ luminescence-based techniques to measure the partial pressure of transcutaneous carbon dioxide monitoring. The first prototype establishes a proof-of-concept system based on a transimpedance-amplifier architecture constructed using off-the-shelf components. This design enables a comparison between ratiometric and intensity-based measurement approaches, while also supporting initial characterization studies of the luminescent sensing film. Building on these findings, the second prototype introduces the first integrated-circuit implementation of a transcutaneous carbon dioxide monitoring system based on a modified delta-sigma modulator. This design adopts an op-amp-less topology that achieves direct current-to-digital conversion, thereby improving power efficiency. An externally implemented current-scaling technique further enhances measurement accuracy at low input current levels without compromising dynamic range. The third prototype advances the level of integration by incorporating the current-scaling mechanism directly on-chip and introducing a new scaling algorithm that delivers improved accuracy across operating conditions. Comprehensive experimental evaluations, including gas-chamber testing and studies conducted with human subjects, validate the functionality and performance of all three prototypes. This work outlines a pathway toward practical, miniaturized transcutaneous carbon dioxide monitoring systems, enabling future deployments in continuous, remote, and wearable healthcare applications.
Advisor:
Ulkuhan Guler
Associate Professor, ECE Department, WPI
Committee Members:
John McNeill
Professor, ECE Department, WPI
Lawrence Rhein
Associate Professor, UMass Chan Medical School