Vital sign monitors are plagued by noisy photoplethysmography (PPG) data, making it difficult for the monitors to output consistently accurate readings. Noise in PPG signals is often caused by motion. The present disclosure provides improved techniques for reducing motion-related artifacts in optical/PPG measurements for vital signs monitoring. In general, techniques described herein are based on using measurements of reference sensors that include sensors other than optical sensors used for the optical measurements, e.g., biopotential sensors, bioimpedance sensors, and/or capacitive sensors. In particular, techniques described herein aim to filter PPG signals using substantially only the noise components of signals generated by reference sensors, by attenuating or altogether eliminating components of the signals generated by reference sensors which are indicative of the parameter the reference sensors are designed to measure. Implementing the techniques described herein may lead to more accurate vital sign evaluation using optical/PPG measurements.
