A Coupling-Adaptive Wireless Power Transfer System With Voltage-/Current-Mode Receiver and Global Digital-PWM Regulation

This article presents a 13.56-MHz wireless power transfer (WPT) system with coupling variation robustness and high efficiency for powering biomedical implantable devices (IMDs). To sustain reliable power transfer against inductive-link fluctuation, a hybrid voltage-/current-mode (V/CM) receiver (RX) is proposed to provide CM recovery when the coupling becomes weak for VM operation. To optimize the end-to-end (E2E) efficiency, a digital pulsewidth modulation (PWM)-based global power regulation technique is proposed, which allows a fully on/off operation of the three-mode power amplifier (PA) at the transmitter (TX) side and fast load-transient responses. Moreover, the system adopts a fully integrated voltage-sensing load-shift-keying (LSK) demodulation technique, which replaces conventional current sensing methods with a streamlined implementation and reduced power consumption. Both prototype TX and RX chips were fabricated in a 180-nm CMOS process. The proposed system, powered by a 1.8-V supply at TX, realizes a regulated 1.8-V dc output at RX. With the help of the hybrid V/CM RX, the proposed system achieves an up-to-150% WPT range extension compared to VM-only operation and an up to 7.2-cm WPT range. Benefiting from the global digital-PWM regulation, it achieves up to 72.3% E2E efficiency over the loading range from 0.18 to 81 mW. A 10- $\mu $ s load-transient recovery is also attained at a $164{\times }$ load step with a 110-mV undershoot and unnoticeable overshoots.