Block, Inc.
Systems and methods for sensing locations of near field communication devices

Abstract:

A system for sensing a proximity of a near field communication (NFC) device includes an NFC reader that communicates with a remote NFC device through load modulation. The NFC reader transmits a wireless carrier signal from an antenna, and the remote NFC device modulates such carrier signal by changing its internal impedance in order to transmit data to the NFC reader. The NFC reader has at least one antenna for receiving the modulated signal. This antenna is coupled to circuitry that measures a spectrum of the received signal and identifies a resonant frequency of the NFC device based on the measured spectrum. Such circuitry also determines the signal's amplitude at such resonant frequency and precisely estimates the distance of the remote NFC device from the reader based on such amplitude. By estimating the precise distance of the remote NFC device from the reader, the location of the remote NFC device relative to the reader can be precisely determined, and this information may be used to operate the NFC reader more efficiently.