Optical sensor and sensing method with stray illumination compensation

摘要

An optical sensor includes an infra red LED, a photodetector and a lock in charge amplifier. The photodetector passes charge to a feedback capacitor of the charge amplifier following an illumination cycle during which the LED is emitting and also following an illumination cycle during which the LED does not emit. An amplifier presents an output indicative of the difference between the charge generated at the photodetector during the illuminated and non-illuminated cycles.