A 196μW, Reconfigurable Light-to-Digital Converter with 119dB Dynamic Range, for Wearable PPG/NIRS Sensors

Abstract

This paper presents a low power, reconfigurable, high dynamic range (DR), light-to-digital converter (LDC) for wearable PPG/NIRS recording. The LDC converts light into the time domain with a dual-slope mode integrator, followed by a counter-based time-to-digital converter. This architecture merges the functionalities of a conventional transimpedance amplifier and ADC, while quantization in time domain significantly improves the DR. The inherent low pulse repetition frequency (PRF) of LDC also reduces the LED power. Furthermore, the DR of the LDC can be easily reconfigured by re-programming the counting step size or the PRF of the LEDs, allowing optimal power consumption for different DR scenarios. The IC achieves a maximum DR of 119dB while only consuming $196 \mu \mathrm {W}($ including 2X LEDs). The IC is validated with PPG and NIRS tests, using photodiodes (PDs) and silicon photomultipliers (SiPMs) respectively.