A CMOS closed-loop miniaturized wireless power transfer system for brain implant applications

Near-field inductively coupled wireless power transfer (WPT) system has been extensively utilized for brain implant applications. Still, the efficient and reliable delivery of power is challenging as the received power varies due to different variabilities between the transmitter (TX) and the receiver (RX) coils. A closed-loop adaptive control system utilizing load shift keying, designed in the 0.5 mu m standard CMOS process for providing the required power to the implant load compensating for these discrepancies is proposed in this paper. Both the proposed TX and the RX coils are fabricated using FR4 substrate having the dimensions of 10 x 10 mm and 5 x 5 mm, respectively. By changing the supply voltage of the power amplifier, this adaptive closed-loop system regulates the transmitted power to deliver 5.83 mW of power to the load, which is the approximate mid-point of the threshold window. The system achieves power transfer efficiencies of 9% and 8% at 8 mm distance through the air and the tissue media, respectively. Preliminary results show that the miniaturized WPT module with the feedback-loop achieves 8% and 3% of efficiency improvement for 8 mm distance between the TX and the RX coils, compared to the open-loop counterparts.