Abstract: A Photoplethysmography-based sensor for measuring heart rate is provided herein. The sensor may include a first light source and a second light source configured to illuminate a body tissue by a first light and a second light respectively; and a first and a second light detectors, each configured to detect light comprising portions of said first light and of said second light, transferred through the body tissue; and a processor with an analog measurement part configured to: receive light intensity readings of at least a portion of light as sensed by each one of both sensors and coming from each one of both sources; and calculate a measure of tissue absorption based on ratios of light portions transmitted by each one of both sources and measured by each one of both detectors.