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.
Stojanovic, R., Asanin, B., & Karadaglic, D. (2009). A fully digital approach in sensing and processing photoplethysmographic signal. In Biomedical Engineering and Informatics, 2009 (BMEI '09) (pp. 1-4). IEEE. https://doi.org/10.1109/BMEI.2009.5305351