Patent ID: 7595729

Claim:
A radio frequency identification (RFID) tag comprising: a tag antenna which receives an input power from an RFID reader and radiates a reflection power corresponding to the input power to the RFID reader; and a tag driver which is electrically connected to the tag antenna, modulates a carrier wave corresponding to the input power, provides the modulated carrier wave and the reflection power to the tag antenna, and adjusts a capacitance according to the intensity of the modulated carrier wave for impedance matching with the tag antenna, wherein the tag driver comprises: an accumulation mode capacitor, the capacitance is changed if the reflection power is higher than a minimum power for backscattering, which modulates the carrier wave and loads the signal wave including the data into the carrier wave, and the minimum power is calculated as below: P bs = P a 4 ×  ρ 1 - ρ 2  2 , where P bs is the minimum power for backscattering, P a is an effective power which is transmitted from the tag antenna and input to the tag driver, ρ 1 is a reflection coefficient if a digital signal value of the signal wave is 0, and ρ 2 is a reflection coefficient when the digital signal value of the signal wave is 1.