A Wireless Hysteretic Controlled Wireless Power Transfer System With Enhanced Efficiency and Dynamic Response for Bioimplants

This article presents a 6.78-MHz wireless power transfer (WPT) system with system-level wireless hysteretic control technique and circuit-level designs for both the receiver (RX) and transmitter (TX) chips. The proposed system achieves RX local voltage regulation and TX global power regulation without using any off-chip components (e.g., MCU, DAC, or various controllers and decoders) nor TX current sensing coils, which were required in previous works. A higher light-load efficiency and instant load-transient response are also achieved with the proposed wireless hysteretic control because of its operation principle. To further improve the efficiency, dynamic switch timing calibrations in the active rectifier in the RX are also designed, with resolved dual steady-state operation issues during the transitions between on-/off-delay compensations. Both the RX and TX chips have been fabricated in 180-nm standard CMOS. Measurement results show a 68.9% peak end-to-end (E2E) efficiency, with an up-to-20% enhancement at light-load conditions over a previous non-linearly controlled WPT system design. When compared to the other state-of-the-art designs, this work achieves an overall higher E2E efficiency, unnoticeable under-/over-shoots with instant recovery in load transients, and a lower system complexity with a higher level of integration without using any extra components other than the LCs to close the wireless loop.