A 1-V 8.1- \mu W PPG-Recording Front-End With > 92-dB DR Using Light-to-Digital Conversion With Signal-Aware DC Subtraction and Ambient Light Removal

• Published in: IEEE solid-state circuits letters Vol. 3; pp. 17 - 20
• Main Authors: Marefat, Fatemeh, Erfani, Reza, Mohseni, Pedram
• Format: Journal Article
• Language: English
• Published: IEEE 01.01.2020
• Subjects: Capacitors; Current measurement; Frequency measurement; Incremental delta–sigma modulator (I–ΔΣM); Integrated circuits; Light emitting diodes; light-to-digital convertor (LDC); Phase measurement; photoplethysmogram (PPG); reconfigurable readout IC (ROIC); Solid state circuits
• ISSN: 2573-9603; 2573-9603
• DOI: 10.1109/LSSC.2019.2957261

This letter reports on a photoplethysmogram (PPG) readout IC (ROIC), comprising an ultralow-power recording front-end and a 2-channel light-emitting diode (LED) driver. The front-end uniquely employs a continuous-time, first-order, incremental delta-sigma modulator (I-AΣM) for direct light-to-digital conversion in a single stage with duty-cycled operation for power savings. Moreover, the I-AΣM enables reconfigurable operation in intermittent conversion phases that allows the direct measurement of dc and ambient light-induced components of the photodiode current for signal-aware on-the-fly cancellation to recover the small ac PPG signal. Fabricated in 0.18-μm 1P/6M CMOS, the PPG ROIC features a high dynamic range of 92.7 dB, dissipates 8.1 μW and 1.95 mW in the recording front-end and the LED (with its driver), respectively, with ~10% duty cycling, and is validated by high-fidelity PPG recording from a human subject fingertip using an infrared LED.