A 40.68-MHz, 200-ns-Settling Active Rectifier and TX-Side Load Monitoring for Minimizing Radiated Power in Biomedical Implants

TL;DR

This paper presents a high-efficiency, fast-settling active rectifier for wireless biomedical implants operating at 40.68 MHz, reducing tissue heating and enabling load monitoring for improved safety and performance.

Contribution

It introduces a novel power efficiency optimization and a 200 ns settling active rectifier fabricated in 40nm CMOS, achieving high efficiency and fast response for implantable devices.

Findings

Achieves 93.9% voltage conversion ratio

Simulated 90.1% power conversion efficiency

Fast 200 ns settling time in active rectifier

Abstract

This letter describes a 40.68 MHz wireless power transfer receiver for implantable applications focused on minimizing tissue heating. The system features a novel power radiated efficiency optimization strategy and a fast-settling active rectifier that maintains high efficiency during load and link variations required for downlink communication. The power radiated efficiency optimization explicitly reduces tissue heating while enabling transmitter-side load monitoring for closed-loop control. The active rectifier was fabricated in 40nm CMOS and achieves a voltage conversion ratio of 93.9% and a simulated power conversion efficiency of 90.1% in a 0.19 $mm^2$ area, resulting in a 118 mW/$mm^2$ power density while integrating the resonance and filter capacitors. The worst-case settling of the on- and off-delay compensation in the active rectifier is 200 ns, which is the fastest reported to date.