A Fully Digital Approach in Sensing and Processing Photoplethysmographic Signal

A fully digital sensor-actuator has been developed for photoplethysmographic (PPG) measurements. Instead of classical sensor it uses standard light emitting diodes (LEDs) for both light emitting and detecting. Time-duration based conversion protocol is implemented by a field programmable gate array (FPGA) avoiding the need for analog amplifiers and precision analogue to digital converters (ADCs). The basic sensing configuration, presented here, consists of a pair of LEDs directly connected to two FPGA´s I/O pins and is capable of detecting the PPG signal from a finger or a toe. The better spectral sensitivity, increased and adjustable resolution, reduced noise, lower cost and dimensions are confirmed advantages. In this paper we introduce a sensing principle in conjunction with pulse-based measurement technique, signal filtering and data communication implemented in a single FPGA chip. The approach in general, as well as the prototype in particular, where evaluated through both qualitative and quantitative experiments.