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

Abstract

Batteryless implantable medical devices (IMDs) require tens of $\boldsymbol{\mu}$W to mW-level power while operating under stringent size constraints and uncertain post-implant orientation. Additionally, high body-channel attenuation necessitates high-ratio voltage multiplication, resulting in slow energy accumulation. This paper presents an 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 $\boldsymbol{\sim}$3.4$\boldsymbol{\times}$ 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 $\boldsymbol{\times}$ 60-stage split-rectifier architecture demonstrates approximately 4$\boldsymbol{\times}$ 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 $\mu$W) and operates with input amplitudes down to $\boldsymbol{\sim}$30 mV, enabling compact, fast-starting, and spatially robust wireless powering for IMDs.