A Reconfigurable Cross-Connected Wireless-Power Transceiver for Bidirectional Device-to-Device Wireless Charging

This paper presents a reconfigurable cross-connected (CC) wireless power transceiver (TRX) operating at 6.78 MHz and implemented for bidirectional device-to-device (D2D) charging with high efficiency and small system volume. We propose, for the first time, a CC topology applied to a differential class-D power amplifier for significant switching loss reduction. Two delay-locked loops (DLLs) for each power NMOS transistor form the reconfigurable controller, realizing the adaptive deadtime control in the transmitter (TX) mode and the off-delay compensation in the receiver (RX) mode, leading to high power conversion efficiency and safe operation. To realize the inductive load for the TX mode in the whole coupling range at the resonant frequency, we use an on-chip tunable capacitor. Furthermore, we also study the power link efficiency in the D2D direct charging system and verify that the near-maximum power link efficiency can be inherently achieved in this scenario. The proposed wireless power TRX, fabricated in a 0.35- \mu \text{m} CMOS process with 5-V devices, measured a peak D2D total efficiency of 77.2% when the output power is 0.7 W. The maximum charging power is 2.74 W with a total efficiency of 62.7% and the maximum transmission distance is 24 mm, both measured.