An Injection-Locked Wireless Power Transfer Transmitter With Automatic Maximum Efficiency Tracking

This article presents a closed-loop transmitter for wireless power transfer with automatic resonance frequency tracking to maintain high efficiency in the over-coupled region. The consists of source oscillator, amplifier (PA), PA driver, matching network, and feedback circuitry. By injecting resonant output coupled antenna coils into oscillator form positive loop, is injection-locked functions as oscillation determined by coils. proposed minimizes change input impedance presented PA, hence mitigates mismatch that causes sharp drop conventional transmitters. Implemented 0.13 μm Bipolar-CMOS-DMOS (BCD) technology, prototype maintains above 60% even at highly spacings (10 mm), which significantly below critical coupling spacing (40 mm). Compared without (i.e., running open loop), distance 10 mm improved 6.6 times charging range over 50% also doubled.