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Sensors 2015, 15(7), 17076-17088;

A Single-Chip CMOS Pulse Oximeter with On-Chip Lock-In Detection

Electrical System and Optics Research Division, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK
Keysight Technologies Belgium NV, Kortrijksesteenweg 1093 B, 9051 Sint Denijs Westrem, Belgium
EDALab-Networked Embedded Systems, Ca Vignal, 2-Strada Le Grazie, 15-37134 Verona, Italy
Author to whom correspondence should be addressed.
Academic Editor: Kwang W. Oh
Received: 21 March 2015 / Revised: 8 June 2015 / Accepted: 6 July 2015 / Published: 14 July 2015
(This article belongs to the Special Issue On-Chip Sensors)
PDF [1323 KB, uploaded 14 July 2015]


Pulse oximetry is a noninvasive and continuous method for monitoring the blood oxygen saturation level. This paper presents the design and testing of a single-chip pulse oximeter fabricated in a 0.35 µm CMOS process. The chip includes photodiode, transimpedance amplifier, analogue band-pass filters, analogue-to-digital converters, digital signal processor and LED timing control. The experimentally measured AC and DC characteristics of individual circuits including the DC output voltage of the transimpedance amplifier, transimpedance gain of the transimpedance amplifier, and the central frequency and bandwidth of the analogue band-pass filters, show a good match (within 1%) with the circuit simulations. With modulated light source and integrated lock-in detection the sensor effectively suppresses the interference from ambient light and 1/f noise. In a breath hold and release experiment the single chip sensor demonstrates consistent and comparable performance to commercial pulse oximetry devices with a mean of 1.2% difference. The single-chip sensor enables a compact and robust design solution that offers a route towards wearable devices for health monitoring. View Full-Text
Keywords: pulse oximetry; SpO2; photoplethysmography; heart rate monitor; smart sensor; lock-in; CMOS sensor pulse oximetry; SpO2; photoplethysmography; heart rate monitor; smart sensor; lock-in; CMOS sensor

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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He, D.; Morgan, S.P.; Trachanis, D.; Van Hese, J.; Drogoudis, D.; Fummi, F.; Stefanni, F.; Guarnieri, V.; Hayes-Gill, B.R. A Single-Chip CMOS Pulse Oximeter with On-Chip Lock-In Detection. Sensors 2015, 15, 17076-17088.

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