Gilbert Hausmann Award 2021 – Antonino Caizzone
An Ultra Low-Noise Micropower PPG Sensor
EPFL thesis n°7946
Thesis directors: Prof. Ch. Enz, Dr A. Boukhayma
For his research, realization and innovations in the field of ultra-low power integrated circuits for vital signs monitoring based on photopletismography (PPG).
Efficient and remote health monitoring is becoming increasingly important, given both the population ageing and the increase in obesity level and cardiovascular diseases. Photoplethysmography (PPG) is a key technology allowing non-invasive monitoring of vitals such as the heart rate, oxygen saturation, respiration rate and blood pressure. A standard PPG system comprises pulsed LEDs synchronized with a photosensor and a processing chain. The LEDs diffuse light in the human skin. Processing the signal held by the diffused light allows the vitals’ extraction. Despite the great potentials behind the PPG technology, the large power burnt by the LEDs represents a challenge towards truly continuous PPG operations. Pinned photodiodes (PPDs) are today the key ingredients of CMOS image sensors, thanks to low noise and large sensitivity operations. The excellent performance of a PPD makes it particularly interesting for the PPG application. Indeed, the LED power can be reduced provided the noise floor is decreased proportionally. In this work a PPD-based micropower PPG sensor is presented. The sensor is implemented in a CMOS image sensor process (CIS) and features 4.6 µW total power consumption, including 1.97 µW LED power. Compared to recent state-of-the-art works this means more than an order of magnitude less power.