A 1–10-MHz Frequency-Aware CMOS Active Rectifier With Dual-Loop Adaptive Delay Compensation and >230-mW Output Power for Capacitively Powered Biomedical Implants

Abstract

This article presents a novel CMOS active rectifier for the emerging modality of capacitive wireless power transfer to biomedical implants with high power budgets. For operation versatility in terms of the input frequency, output power level, input voltage range, and load value, dual-loop adaptive delay compensation is utilized to provide both high resolution and high dynamic range in switched-offset currents of comparators that can be reconfigured for low- and high-speed operation modes for automatic adaptation to the input frequency. Fabricated in 0.18 $\mu \text{m}$ 1P/6M CMOS, the rectifier features power conversion efficiency (PCE) of >84.4% (peak of 91.5%) and voltage conversion ratio (VCR) of >88.6% (peak of 95.1%) when operating in 1–10 MHz and driving a load of 300 $\Omega $ . Moreover, for a load range of 20 $\Omega $ –1 $\text{k}\Omega $ at 5 MHz, PCE of 81%–91.8% and VCR of 78.4%–95.4% are achieved, with a maximum output power of ~232 mW at 50 $\Omega $ with a PCE of 90.1%. The active rectifier is also interfaced with a series-resonant capacitive link formed with coated flexible copper plates around a 3-mm-thick layer of muscle tissue, demonstrating an end-to-end power transfer efficiency of >40% in 2–10 MHz and with a load of 300 $\Omega $ .