A Nonuniform Sampling Lifetime Estimation Technique for Luminescent Oxygen Measurements for Biomedical Applications

• Published in: IEEE journal of solid-state circuits Vol. 60; no. 8; pp. 2905 - 2919
• Main Authors: Costanzo, Ian, Sen, Devdip, McNeill, John, Guler, Ulkuhan
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.08.2025; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplifiers; Analog-to-digital converter (ADC); Biomedical materials; Biomedical optical imaging; Blood; blood gases; Capacitors; Estimation; light-to-digital converter (LTC); Luminescence; luminescent measurements; Noise; nonuniform sampling (NUS); Occlusion; Optical amplifiers; Optical sensors; Optical variables measurement; Oxygen; oxygen sensor; Signal processing algorithms; Subsystems; Time constant; Time measurement; transcutaneous sensing; luminescent measurements; nonuniform sampling (NUS); Analog-to-digital converter (ADC); light-to-digital converter (LTC); transcutaneous sensing; oxygen sensor; blood gases
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2024.3512472

This article presents a novel technique that is immune to offset, enabling precise determination of the lifetime of luminescent materials. The technique is specifically applied to measure transcutaneous oxygen, an indicator of oxygen that diffuses through the skin and reflects arterial oxygen levels. Unlike intensity-based measurements, lifetime-based luminescence measurements are superior because they decouple oxygen information from confounding factors. The technique presented in this work involves measuring the time difference between fixed-voltage steps to extract the time constant of a decaying exponential, which represents the lifetime of luminescence. We propose a novel switched-capacitor circuit that enables long integration times and prevents the front-end amplifier from saturating. The analog subsystem was realized in 180-nm CMOS technology via a transimpedance amplifier (TIA) with a gain bandwidth product of 10 MHz, a comparator, and a switched capacitor circuit. The measured mean error is as accurate as 1.9% without postprocessing. During a <inline-formula> <tex-math notation="LaTeX">130~{\mu } </tex-math></inline-formula>s measurement period, the readout circuit consumes a maximum of <inline-formula> <tex-math notation="LaTeX">16~{\mu } </tex-math></inline-formula>J per calculation with a <inline-formula> <tex-math notation="LaTeX">{\text {FoM}_{W}}{=}177 </tex-math></inline-formula> nJ/conv. Preliminary human subject tests have demonstrated that the sensor can effectively detect changes in transcutaneous oxygen levels resulting from arterial occlusion.