17.8 A 2.6μW Monolithic CMOS Photoplethysmographic Sensor Operating with 2μW LED Power

Photoplethysmography (PPG) is a key technology allowing non-invasive monitoring of vital indicators such as heart rate (HR) and oxygen saturation (SpO2). Today, the total PPG sensor power consumption is dominated by the few tens of mA of the LEDs driving current. Different solutions have been proposed to solve this bottle-neck, either by reducing the LED duty cycle [1], [2] or by nonuniform sub-sampling [3]. A heart-beat-locked loop system that significantly reduces the LED power has been recently demonstrated [4]. However, this power reduction comes at the cost of more complexity since it requires a non-trivial heart beat prediction scheme and intrinsically hinders the full PPG wave representation.