Abstract
Photoplethysmography (PPG) has emerged as a highly convenient and non-invasive technique for assessing heart rate and its variability in wearable health monitoring devices. However, a drawback lies in the energy demand of PPG systems which consequently increases the average power consumption of the wearable devices integrated with PPG sensors. In this paper, we present our efforts towards packaging a novel compressed-sensing (CS) based ultra-low power PPG application-specific integrated circuit (ASIC) into a wearable device and testing it through a preclinical human study. The system comprises a custom-designed PPG analog front-end circuit, integrated with a digital back-end to implement CS, a light source-detector pair, and a commercial off-the-shelf microcontroller for Bluetooth Low Energy (BLE) based wireless data transfer. Two circular PCBs, a general-purpose main board containing the microcontroller and a plugin board housing the ASIC interfacing components, fit into a wristband form factor. This modular architecture of the wristband platform allows for the incorporation of other environmental sensors for future correlated sensing studies between health and the environment. The PPG ASIC consumes 172 $\bm {\mu }$ W power to extract heart rate from the sparse PPG signal whereas the whole system consumes 1.66 mW power for continuous streaming of heart rate data over the BLE radio which can be further duty cycled. The preclinical trial of the platform demonstrated its efficacy in assessing accurate heart rate in comparison to commercial PPG and electrocardiography systems. This work presents the first-ever demonstration of a wearable wristband with CS based PPG performed on a chip.