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<inline-formula> <tex-math notation="LaTeX">$_{\mathrm{H}}$</tex-math> </inline-formula> <inline-formula> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 3-V, V<inline-formula> <tex-math notation="LaTeX">$_{\mathrm{L}}$</tex-math> </inline-formula> <inline-formula> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 1.8-V) regulated by adaptive power control (APC) and local-loop power control. Due to transmission power regulation (TPR), the transmitter (<inline-formula> <tex-math notation="LaTeX">$T_{X})$</tex-math> </inline-formula> delivers appropriate power to the receiver (<inline-formula> <tex-math notation="LaTeX">$R_{X})$</tex-math> </inline-formula> 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<inline-formula> <tex-math notation="LaTeX">$_{X}$</tex-math> </inline-formula> power conversion efficiency (PCE). <inline-formula> <tex-math notation="LaTeX">$T_{X}$</tex-math> </inline-formula> and <inline-formula> <tex-math notation="LaTeX">$R_{X}$</tex-math> </inline-formula> chips were fabricated in a 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m CMOS process. The measurement results show that the proposed WPT system successfully regulates outputs at V<inline-formula> <tex-math notation="LaTeX">$_{\mathrm{H}}$</tex-math> </inline-formula> <inline-formula> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 3-V and V<inline-formula> <tex-math notation="LaTeX">$_{\mathrm{L}}$</tex-math> </inline-formula> <inline-formula> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 1.8-V at a 1.5-cm coupling distance. With the proposed TPR, PTE is improved by 28.2% at P<inline-formula> <tex-math notation="LaTeX">$_{\mathrm{TOTAL}}$</tex-math> </inline-formula> <inline-formula> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 1.6-mW, and input power is reduced by 94.8% at P<inline-formula> <tex-math notation="LaTeX">$_{\mathrm{TOTAL}}$</tex-math> </inline-formula> <inline-formula> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 1-mW. The measured peak PCE and peak PTE are 85.1% and 31.3% at a coil distance of 10-mm, respectively.