Patent ID: 8786504

Claim:
A circuit capable of automatically calibrating a resonant frequency of an antenna, the circuit comprising: an antenna having a first terminal, and a second terminal for receiving an electric wave transmitted by a reader; a switch having a first terminal coupled to the second terminal of the antenna, a second terminal coupled to ground, and a third terminal for receiving a pulse; a conversion unit having a first terminal coupled to the second terminal of the antenna for receiving a signal with the resonant frequency of the antenna, and a second terminal for outputting a clock, wherein the conversion unit is used for generating the clock according to the signal, and the clock is a digital square wave; a count comparator having a first terminal coupled to the second terminal of the conversion unit, and a second terminal for outputting an adjustment signal, wherein the count comparator is used for counting a number generated by a reference clock during a period of the clock, and comparing the number with a predetermined value to generate the adjustment signal; a capacitor array for adjusting a value of the capacitor array according to the adjustment signal.