33.6 A Wireless Power Transfer System with Up-to-20% Light- Load Efficiency Enhancement and Instant Dynamic Response by Fully Integrated Wireless Hysteretic Control for Bioimplants
Junyao Tang, Lei Zhao, Cheng Huang
Abstract
Wireless power transfer (WPT) systems are becoming increasingly popular for sub100mW biomedical applications [1] -[5]. Because the received power is sensitive to coupling and loading conditions, power/voltage regulations are essential to achieve stable and accurate power delivery, fast transient response, and high end-to-end (E2E) efficiency, which includes all the power losses in the transmitter (TX), wireless power link, and the receiver (RX). Many existing WPT designs operated in open-loop [3] -[5]; or achieved voltage regulation but only in the RX [6], with the TX remained unregulated and designed to operate at full capacity, thus degraded E2E efficiency at light-load conditions. Because lower-power or standby mode typically contributes to the majority of the operation time, light-load efficiency is always an important specification of power management circuits, especially to extend the run time for battery-powered devices, e.g., a wearable/portable WPT transmitter supporting bioimplants. [1], [2], [7] -[9] have reported different approaches to achieve TX regulation; however, all required extra discrete components, which increased the form-factor and cost. [7], [8] required a wire to close the loop. [1], [2], [9] utilized load-shift-keying (LSK) backscattering for TX regulation, which was proved an effective solution. However, [2], [9] relied on lots of off-chip components, including power inductors, diodes, DACs, FPGAs, etc., due to the analog control methodologies. The linear control also introduced small-signal bandwidth limitations, which required careful design to ensure stability at different loading/coupling conditions with PVT/component variations, and resulted in significant compromise in dynamic performance. [1] introduced a nonlinear constant-idle-time control to eliminate the bandwidth limitations and most of the off-chip components; however, the light-load efficiency still suffered. In addition, [1] still required an extra sensing coil to extract LSK signals that increased the TX coil area by 86%.