A system includes a tank circuit, a synchronization circuit, a transmitter, and a control circuit. The tank circuit is configured to receive a first signal transmitted from a near field communication reader. The synchronization circuit is configured to synchronize a clock to the first signal. The transmitter is configured to transmit data using the clock from the tank circuit to the near field communication reader using active load modulation. The control circuit is configured to disable the synchronization circuit during a modulation period of the active load modulation and to reduce energy remaining in the tank circuit at an end of the modulation period.

Clock recovery system and method for near field communication with active load modulation

An example method for active load modulation includes determining a modulated portion and an unmodulated portion of a bit. Further, the example method includes during the modulated portion of the bit, holding a phase of a received carrier signal. In addition, the example method includes, during the unmodulated portion of the bit, synchronizing to the received carrier signal.

Active load modulation in near field communication

Embodiments of methods and systems for operating a communications device that communicates via inductive coupling are described. In an embodiment, a method for operating a communications device that communicates via inductive coupling involves detecting a system condition associated with the communications device and tuning a matching network of the communications device in response to the system condition, where the matching network includes a hybrid transformer that separates a receiver of the communications device from a transmitter of the communications device. Other embodiments are also described.

Method and system for operating a communications device that communicates via inductive coupling

Embodiments of the invention provide a system and method for direct RF sampling a Near Field Communication (NFC) receiver at a rate higher than the carrier frequency by reducing and shifting requirements at a front end analog module to a digital module.

Apparatus and method for direct radio frequency (rf) sampling in near field communication (nfc) devices

The invention provides a near field communication device used for preparing carrier signals for active load modulation supporting synchronous and asynchronous transmission. The NFC device includes: alocal clock generator for generating a reference clock signal (REF_CLK); a clock extractor for recovering a clock signal (EXT_CLK) generated by an NFC initiator device; a frequency tracking module FTMfor executing frequency tracking operation to generate FTM output with the frequency being aligned with the frequency of the input clock signal (REF_CLK or EXT_CLK); and a phase tracking module PTM which performs a phase tracking operation on the FTM output based on EXT_CLK to generate a PTM output with phases being aligned with phases of EXT_CLK. The PTM output acts as the carrier signals at a desired frequency and phase for load-modulating the data of the NFC device to form a load-modulated signal for active transmission to the NFC initiator device.

An active load modulation technology in near field communication

In some aspects, the disclosure is directed to methods and systems for carrier synchronization in active load modulation for near field communications. A broadcast carrier is received from a remote device and mixed with a locally-generated carrier and modulated data. A carrier synchronization circuit synchronizes the locally-generated carrier with the broadcast carrier based on an identified phase error from a double Cartesian-to-polar mapping of the mixed locally-generated carrier and broadcast carrier. In some implementations, the system also includes a modulation suppression circuit for providing unmodulated carrier signals to the carrier synchronization circuit or suppressing modulation distortion to maintain frequency and phase tracking despite the presence of data.

Dong-U Lee

Papers

Carrier synchronization appropriate for alm nfc data transmission