A 6.78-MHz Wireless Power Transfer System With Dual-Output Resonant Current-Mode Regulating Rectifier and Transmission Power Regulation

This paper introduces a 6.78-MHz wireless power transfer (WPT) system for implantable medical devices (IMDs). The proposed dual-output resonant current-mode (RCM) rectifier cumulates energy from loosely-coupled coils and generates two output voltages (V-H = 3-V, V-L = 1.8-V) regulated by adaptive power control (APC) and local-loop power control. Due to transmission power regulation (TPR), the transmitter (T-X) delivers appropriate power to the receiver (R-X) to realize global-loop power control. Thus, the power transfer efficiency (PTE) is improved, especially under light load. Furthermore, zero-voltage switching and zero-current switching techniques enhance R-X power conversion efficiency (PCE). T-X and R-X chips were fabricated in a 0.18-mu m CMOS process. The measurement results show that the proposed WPT system successfully regulates outputs at V-H = 3-V and V-L = 1.8-V at a 1.5-cm coupling distance. With the proposed TPR, PTE is improved by 28.2% at P-TOTAL = 1.6-mW, and input power is reduced by 94.8% at P-TOTAL = 1-mW. The measured peak PCE and peak PTE are 85.1% and 31.3% at a coil distance of 10-mm, respectively.