A 0.18 μm CMOS Integrated Optical Wireless Power Transfer System for Implantable Biomedical Devices

This paper reports on a fully integrated optical wireless power transfer system designed for implantable biomedical devices. If compared with the solutions based on radiative and non-radiative methodologies, like the capacitive, inductive, magnetic couplings and radio frequency techniques, the optical systems reach the highest electromagnetic compatibility respect to the simultaneous presence of other electronic instrumentations. A further advantage common to all the radio frequencies, is the capability to transfer power to implantable and wearable biomedical devices also from long distances using environmental visible and near infrared light and/or LED-based lamps. The proposed solution has been designed at transistor level in TSMC 0.18 mu m CMOS technology using inverter stages with the aim to maximize the output voltage value starting from low input voltages coming from a Si photodiode, also included in the overall layout of the system that requires a total Si area of about 0.466 mm(2), By performing post-layout simulations, considering a minimum input voltage as low as 0.5 V, the achieved output voltage is higher than 2 V that increases up to 3.4 V for an input voltage of 0.7 V, with a best power conversion efficiency of about 70 %. The comparison of the main characteristics of the proposed solution with the State-of-Art demonstrates that, starting from the lower input voltages, the proposed system is capable to work with a reduced clock frequency achieving higher output voltages to supply external loads, satisfactory output currents and good power conversion efficiencies, requiring a reduced Si area.