Improving Wireless Power Transfer Efficiency for Distributed Brain Implants using Auto-Tune OVP.

Wireless sub-mm-sized distributed brain implants could revolutionize Brain-Machine Interface applications by providing untethered cortical recording and/ or stimulation with unprecedented density. A key to achieving this goal is the development of wireless power transfer (WPT) methods that operate in this spatially varying magnetic field. We demonstrate, through circuit simulations and theoretical analysis, over-voltage protection (OVP) realized by circuit resonance auto-tuning will significantly enhance the overall system WPT efficiency by 5dB over the traditional OVP voltage clamping method. The auto-tune algorithm is designed and measured in a completely integrated 65nm CMOS ASIC implant featuring necessarily low power and small size. Additionally, a solution is implemented to avoid an inherent cold start issue that would otherwise significantly constrain auto-tune WPT implementations.