Open-Loop Frequency Lock Methods for Fast Boot-Up Time

摘要

A method for a near field communication circuit includes entering a low power mode and subsequently determining to exit the low power mode. The method further includes generating an open loop clock signal and providing the open loop clock signal to circuits of the near field communication circuit during a low power mode exit duration. Subsequently a reference clock signal is received from a host and used to clock the near field communication circuit.

主权项

1. A near field communication (NFC) circuit comprising:
challenge detection circuitry responsive to a clock signal and operative to detect a challenge received from an NFC reader, the challenge requiring a response by the NFC circuit to the NFC reader within a standardized, predetermined response time; a frequency locked loop responsive to a digital word to generate an open loop clock signal as the clock signal at a frequency controlled by the digital word, the frequency locked loop selectively operable in a low power mode to reduce power consumption; and a memory in data communication with the frequency locked loop and to be continuously powered when the frequency locked loop is operated in the low power mode, the memory configured make the digital word immediately available to the frequency locked loop upon exit from the low power mode by the frequency locked loop so that the frequency locked loop may provide the open loop clock signal to the challenge detection circuitry to detect the challenge from the NFC reader for response to the challenge by the NFC circuit within the standardized, predetermined response time.