An RFID IC may operate at a relatively low clock frequency while impedance matching to an antenna is being tuned to increase the amount of power that the IC can extract from an incident RF wave. A tuning circuit tunes the impedance matching by adjusting a variable impedance coupling the IC and the antenna. The IC may power-up with a low clock frequency or reduce its current clock frequency to a lower clock frequency prior to tuning or during the tuning process, and may increase its clock frequency upon completion of tuning or during the tuning process.

An RFID IC may operate at a relatively low clock frequency while impedance matching to an antenna is being tuned to increase the amount of power that the IC can extract from an incident RF wave. A tuning circuit tunes the impedance matching by adjusting a variable impedance coupling the IC and the antenna. The IC may power-up with a low clock frequency or reduce its current clock frequency to a lower clock frequency prior to tuning or during the tuning process, and may increase its clock frequency upon completion of tuning or during the tuning process.

The present disclosure provides systems and devices including reception circuits for communications between smart cards and card readers. In some embodiments, a reception circuit of a smart card includes a first circuit and a second circuit. The first circuit is configured to receive a wireless signal including a pause, and restore the wireless signal to a clock signal. The second circuit is configured to charge a voltage of a first node based on a first logic level of the clock signal, compare the voltage of the first node with a predefined reference voltage, and output, based on the comparison of the voltage of the first node, a synchronization signal indicating a rising starting time point of the pause of the wireless signal.

A smart card includes a frequency measurement circuit configured to measure a first clock frequency of an external clock signal, a sensor clock output circuit configured to select a first range from a plurality of first clock ranges based on the first clock frequency and to output a sensor clock signal having a second clock frequency corresponding to the first range, and a sensor circuit configured to output sensing data for biometric authentication based on the sensor clock signal and first compensation image data.

A method of a reader may comprise: generating a physical reader-to-device channel (PRDCH) preamble including a first preamble and a second preamble; generating a reader-to-device (R2D) signal including the PRDCH preamble and a PRDCH; and transmitting the R2D signal to a device, wherein the PRDCH preamble is located before the PRDCH in time domain.

A method of a reader may comprise: generating a physical reader-to-device channel (PRDCH) preamble including a first preamble and a second preamble; generating a reader-to-device (R2D) signal including the PRDCH preamble and a PRDCH; and transmitting the R2D signal to a device, wherein the PRDCH preamble is located before the PRDCH in time domain.