A <25 μW CMOS monolithic photoplethysmographic sensor with distributed 1b delta-sigma light-to-digital convertor

Abstract

This paper presents CMOS monolithic PPG sensor with distributed 1b delta-sigma light-to-digital convertor (LDC). Proposed unbiased photodiode (PD) based circuit with fully integrated PD in the same die efficiently performs direct light to digital conversion, and the distributed architecture further improves the dynamic range. The implemented sensor, fabricated in standard 0.18μm CMOS process, achieves 20.4 pA rms equivalent noise with <25 μW power consumption, and successfully performs a reflective PPG measurement at wrist and finger, with both pulsed and continuous LED light.