Design and simulation of an integrated optical CMOS heart rate sensor

An optical CMOS heart rate sensor that processes the photoplethysmographic signal was designed and fabricated in Austriamicrosystems 0.35μm CMOS process. The sensor consists of photodiode, transimpedance amplifier, analogue bandpass filters, analogue-to-digital converters, digital signal processor, and a timing circuit that is used to modulate the external light-emitting diodes. The mixed-signal simulation has been carried out to validate the system design. With modulated green light source and integrated lock-in detection the sensor is capable of extracting clean photoplethysmographic signal when it is operated in reflectance mode. The heart rate output was compared with commercial devices and they show a good agreement. The chip-level integration enables a small foot print of the design and makes it suitable for the applications of ambulatory monitoring.