Toward low-power PPG-based heart rate monitoring using a MOS-PN hybrid photosensor

This paper focuses on the design of a low-power PPG-based heart rate monitoring system based on a MOS-PN hybrid photosensor. The latter performs a direct light-to-time conversion, allowing to use a fully digital light-to-digital conversion and avoiding the need for an area- and power-consuming analog front-end. The proposed PPG sensing interface is analyzed both theoretically and experimentally. The relationship between accuracy and power consumption proves to be defined by the shot noise, making the MOS-PN photodiode a good candidate for replacing standard photodiodes. Additionally, the obtained PPG signal is processed by a specifically designed algorithm with low requirements on the input data, allowing an ultra low power PPG sensing and paving the way toward permanent heart rate monitoring by wearable devices.