A pulse oximeter based on time-of-flight histograms

Yuanyuan Hua*, Konstantinos Bantounos, Aravind Venugopalan Nair Jalajakumari, Alex Turpin, Ian Underwood, Danial Chitnis

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution


A pulse oximeter is an optical device that monitors tissue oxygenation levels. Traditionally, these devices estimate the oxygenation level by measuring the intensity of the transmitted light through the tissue and are embedded into everyday devices such as smartphones and smartwatches. However, these sensors require prior information and are susceptible to unwanted changes in the intensity, including ambient light, skin tone, and motion artefacts. Previous experiments have shown the potential of Time-of-Flight (ToF) techniques in measurements of tissue hemodynamics. Our proposed technology uses histograms of photon flight paths within the tissue to obtain tissue oxygenation, regardless of the changes in the intensity of the source. Our device is based on a 45ps time-to-digital converter (TDC) which is implemented in a Xilinx Zynq UltraScale+ field programmable gate array (FPGA), a CMOS Single Photon Avalanche Diode (SPAD) detector, and a low-cost compact laser source. All these components including the SPAD detector are manufactured using the latest commercially available technology, which leads to increased linearity, accuracy, and stability for ToF measurements. This proof-of-concept system is approximately 10cm×8cm×5cm in size, with a high potential for shrinkage through further system development and component integration. We demonstrate preliminary results of ToF pulse measurements and report the engineering details, trade-offs, and challenges of this design. We discuss the potential for mass adoption of ToF based pulse oximeters in everyday devices such as smartphones and wearables.

Original languageEnglish
Title of host publicationPhotonic Instrumentation Engineering VIII
EditorsYakov Soskind, Lynda E. Busse
ISBN (Electronic)9781510642218
Publication statusPublished - 5 Mar 2021
EventPhotonic Instrumentation Engineering VIII 2021 - Virtual, Online, United States
Duration: 6 Mar 202111 Mar 2021

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferencePhotonic Instrumentation Engineering VIII 2021
Country/TerritoryUnited States
CityVirtual, Online


  • histogram
  • pulse oximeter
  • time to digital converter (TDC)
  • time-of-flight (Tof)


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