A 13.56 MHz Wireless Power Transfer System With Fully Integrated PLL-Based Frequency-Regulated Reconfigurable Duty Control for Implantable Medical Devices

In this paper, a 13.56 MHz wireless power transfer system with transmitter (TX) and receiver (RX) chips is presented. Both TX and RX chips were designed with fully integrated reconfigurable single power stage to realize adaptive power delivery and output voltage regulation. The reconfigurable operation of TX and RX is synchronized and the reconfiguration frequency which could vary with coupling or loading condition is locked by the proposed phase-locked-loop-based on-time duty controller to mitigate the electromagnetic interference. In addition, calibrations for circuit delay and power switch size were implemented in the RX chip to enhance system efficiency further. The system complexity is reduced considerably by removing the successive power stages and off-chip controllers used in previous studies. The TX and RX chips were fabricated in TSMC 0.18 μm CMOS process. The measurement results demonstrated seamless output voltage regulation under an output power range from 4.2 mW to 162 mW and a peak end-to-end efficiency of 70.1%.