A PPWM-Based CMOS Wireless Power Charger With Active Bias-Clamp Cascode Biasing and Load-Adaptive Rectifier Sizing

This paper presents a wireless charging system for implantable medical devices, implemented in TSMC 0.18 um 1P6M CMOS and operating at 6.78 MHz with a single resonant coil pair. The proposed system supports a battery charging voltage range of $2.6\sim 4.2$ V, covering trickle-charge (TC), constant-current (CC), constant-voltage (CV), and direct power (DP) modes. The charger provides a constant output current ranging from 5 mA to 50 mA. The overall system achieves a peak efficiency of 88.9 %. The Active Bias-Clamp Cascode scheme is introduced to suppress over-voltage stress while significantly reducing the required bias capacitance, while the Load-Adaptive Rectifier Sizing (LARS) technique dynamically adjusts the rectifier conduction channel size according to load conditions. These techniques together improve efficiency and ensure robust operation across wide load variations, making the system well suited for highly constrained implantable applications.