A 40.68‐MHz Wireless Power Transfer System With Hybrid Delay‐Compensated Rectifier and Global Digital Scheduled Power‐Down Regulation for Bioimplants

ABSTRACT This article presents a fully integrated 40.68‐MHz wireless power transfer (WPT) system for miniaturized implantable medical devices (IMDs). Operating at 40.68 MHz enables the use of a 4‐mm receiver coil but introduces challenges in switching losses and delays. To address these, three techniques are proposed. First, a hybrid delay‐compensated active rectifier combining PWM and voltage‐controlled delay line (VCDL) enables zero‐voltage switching with low quiescent power. Second, a global digital scheduled power‐down regulation (DSPDR) scheme periodically deactivates the transmitter power amplifier during idle intervals, significantly improving light‐load end‐to‐end (E2E) efficiency. Third, a digital adaptive threshold control ensures reliable load‐shift keying demodulation against coupling variations. Fabricated in 180‐nm CMOS, the receiver achieves a peak power conversion efficiency of 89.4%. The system demonstrates a peak E2E efficiency of 63.4% and maintains a high E2E efficiency of 46.6% at a light load of 1 mA, representing a significant improvement over state‐of‐the‐art designs.