A CMOS Fully Integrated Optical Wireless Power Transfer SoC for Biomedical IoT Devices

This paper reports on the design and experimental characterization of a fully integrated optical wireless power transfer for biomedical internet-of-things devices. The solution has been fabricated on-chip in TSMC <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu $ </tex-math></inline-formula>m standard Si CMOS technology within an area of 0.466 mm2 integrating a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500\times 500~\mu $ </tex-math></inline-formula>m2 Si photodiode. If compared with the solutions using different methodologies, optical wireless systems allow for reaching the highest electromagnetic compatibility with the further advantage of transferring electrical power from long distances. The architecture employs inverter stages to maximize the value of the achievable output voltage starting from the input voltage and currents provided by the integrated photodiode. The electrical and optical characterizations of the fabricated device were performed under both continuous and pulsed operation modes. Depending on the impedance of the external load to be powered, output voltages up to 2.45 V have been obtained from an input voltage of 0.35 V with an energy conversion efficiency of 58 %. The comparison of the main features achieved with those of similar solutions reported in the Literature has been performed. By employing low input voltages, the proposed system requires a reduced Si area, works at a lower clock frequency, achieves the higher output voltages to supply external loads with satisfactory output currents and good energy conversion efficiencies.