WPT and NFC Interoperability for Wearables with Miniaturized Coils

This work presents a circuit-level interoperability investigation of a wireless power transfer (WPT) and nearfield communication (NFC) system using miniature coils suited for wearables. Interoperability could enable NFC to provide a communication link for a WPT system or enable secure pairing between a wearable and a WPT transmitter. The WPT and NFC circuitries are built in a circuit-level simulation tool. The coils are modeled by a broadband equivalent circuit model, which excellently agrees with measurements from 0.1 to 500 MHz. The resulting equivalent circuit model is used to investigate the tag-to-reader communication quality via in-phase (I) and quadraturephase (Q) demodulation and signal constellation diagrams. It is shown that applying inductive decoupling techniques between WPT and NFC coils and altering the I/Q demodulation filter cut-off frequency can significantly improve the tag-to-reader communication quality.