US Patent 11916619 Auto-tuner for resonant circuit

A tuning circuit for a near-field magnetic induction (NFMI) system suitable for near field communication (NFC) is disclosed. The NFMI system includes a tuning circuit that is configured to measure a phase across a series capacitor coupled between a resonant circuit and a transmit circuit in order to determine a resonant condition of the resonant circuit. When the resonant condition is above resonance or below resonance, the tuning circuit can tune an adjustable capacitor of the resonant circuit. The tuning can continue until the phase measurement indicates that the resonant circuit is at resonance. The phase-based tuning allows for the tuning to operate continuously and concurrently with NFC.