Adaptive Impedance Matching with Fault Ride Through in Wireless Power Transfer for Implanted Medical Devices

IMDs has found widespread application across various medical fields. Wirelessly powered implants are increasingly being developed to interface with neurons due to its small size. The matching network (MN) within the wireless IMD is a crucial component influencing system efficiency. Conventional approaches using fixed-value MNs struggle to adapt to changes in parameters and environment. This research proposes an adaptive algorithm-based MN that enabels the system to automatically track the maximum rectified voltage despite variations in frequency and inductor, as well as sampling errors due to random external interference. For the first time, an active voltage limiter has been integrated into the MN to reject excess power in order to safeguard the chip, rather than dissipating it as heat. Implemented in TSMC 65nm technology, this system can operate under ±15% inductance fluctuation and ±10% frequency fluctuation at 500 MHz, enabling unusable systems to obtain sufficient power. The chosen proof-of-concept for this work is a neural stimulating IMD but this approach can extend beyond this setup.