A Fast-Charging Inductive-Capacitive Dual-Mode Orthogonal Orientation-Independent Switched-Mode Wireless Power Transfer System for Battery-Less Implantable Medical Devices in 65nm CMOS.

Batteryless implantable medical devices (IMDs) require tens of μW to mW-level power while operating under stringent size constraints, uncertain post-implant orientation, and high body-channel attenuation that forces high-ratio voltage multiplication and slow energy accumulation. This paper presents a Inductive-Capacitive dual mode wireless power transfer (WPT) system that improves charging latency and link robustness by combining three techniques: (i) a split rectifier (REC) architecture with temporal energy combining to mitigate stage-leakage and accelerate energy accumulation, (ii) an orthogonal coil-fed cuboid receiver that provides spatially neutral (orientation-independent) operation, and (iii) dual-mode inductive-capacitive powering by reusing the same conductors as both inductive coils and capacitive electrodes. A load-isolating switch (LIS) further suppresses leakage during startup, reducing the average load-leakage. Fabricated in 65-nm CMOS, the 0.19 mm² prototype achieves ~3.4× faster charging compared to the TEG/solar based prior-art design. In addition, under identical input conditions of -12 dBm at 70 MHz, the proposed 4 × 60-stage split-rectifier architecture demonstrates approximately 4× reduction in charging time compared to a conventional 240-stage implementation. The WPT system achieves a minimum input power sensitivity of -26 dBm (2.5 μW) and operates with input amplitudes down to ~30 mV, enabling compact, faststarting, and spatially robust wireless powering for IMDs.