Double junction photodiodes for multiwavelength photoplethysmography

João Costa, Hugo Vieira, Paula Louro, Manuela Vieira

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

3 Citations (Scopus)


Oxygen saturation levels in blood are usually measured with photoplethysmography (PPG) using two LEDs, one in the red and the other in the near infrared region of the spectrum. A number of studies have increased the number of wavelengths, not only to improve the accuracy of SpO2 measurements, but also to provide real-time measurements of other substances in blood, such as methemoglobin and carboxyhemoglobin. In addition, analysis of PPG signals at different wavelengths could provide information about skin pathologies at various tissue depths. In this work we study the advantages of using photodetection based on vertically stacked double junction photodiodes. The sensitivity of such photodetectors over a wider wavelength range is of particular interest for PPG. We have implemented a test bed, which includes the control of light sources to emulate the transmitted signals, the analog front-end to recover the time multiplexed PPG signals and post-processing to calculate the hemoglobin fractions. We use this framework to compare results of photodetection obtained using a single silicon junction and the combination of a silicon and indium gallium arsenide junction for photodetection.

Original languageEnglish
Title of host publicationOptical Sensing and Detection V
PublisherSPIE-International Society for Optical Engineering
ISBN (Electronic)9781510618862
Publication statusPublished - 9 May 2018
EventOptical Sensing and Detection V 2018 - Strasbourg, France
Duration: 23 Apr 201826 Apr 2018

Publication series

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


ConferenceOptical Sensing and Detection V 2018


  • multiwavelength
  • oximetry
  • photodiodes
  • PPG


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