Development and Validation of Offset Current Compensation Technique for Optical Sensors

Optical sensors are widely used in a variety of industrial, scientific and healthcare applications. The offset current due to ambient light affects the overall performance of such sensor system. This is even more critical in biomedical applications such as photoplethysmography (PPG) and functional-near infrared spectroscopy (fNIRS). The continuous offset cancellation technique introduce the delay and affects the shape morphing of such signals. In this paper, we present a mixed-signal based discrete offset cancellation technique for effective compensation of the offset current of the optical sensors for biomedical applications. The system is based on a feedback loop which calibrate the offset and compensate it at the start of recording. A prototype of the system is built and tested for PPG signal recording. The results shows that the proposed system is able to effectively compensate the offset current.