RFID tag and RFID system having the same

• US 7,595,729 B2
• Filed: 10/20/2006
• Issued: 09/29/2009
• Est. Priority Date: 01/20/2006
• Status: Expired due to Fees

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Seong-hearn, Lee, Dong-hyun, Ku, Ja-nam
• Primary Examiner(s): Wu; Daniel
• Assistant Examiner(s): GIRMA, FEKADESELASS
• Application Number:
  US11/583,936
• Publication Number:
  US 20070171065A1
• Time in Patent Office: 1,075 Days
• Field of Search: 340/572.1, 340/10.4, 340/10.42, 340/235, 340/435, 340/436, 340/449, 340/451, 455/41.1, 455/41.2, 455/41.3, 343/822, 343/860, 343/861, 343/913
• US Class Current: 340/572.1
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: H01L 27/0727 in combination with diodes, or capacitors or resistors
• CPC Class Codes: H01L 29/93 Variable capacitance diodes, e.g. varactors
• CPC Class Codes: H01L 29/94 Metal-insulator-semiconductors, e.g. MOS

Abstract

An RFID tag capable of enhancing the reliability of products and an RFID system having the same are provided. The RFID tag includes a tag antenna receiving waves from an RFID reader, and a tag driver. The tag driver includes an accumulation mode capacitor adjusting a capacitance value corresponding to an input voltage. That is, the tag driver adjusts the amplitude of a modulated carrier wave using the accumulation mode capacitor. Accordingly, the RFID tag adjusts the impedance of the tag driver without adjusting the current transmitted from the tag driver. Therefore, impedance adjustment of the tag driver can prevent the voltage transmitted from the tag driver from being lower than the reference voltage, and modulation and demodulation can be stably performed. As a result, the reliability of products can be enhanced.

Claims

1. 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;

$P_{\mathrm{bs}}=\frac{P_a}{4}\times <br><br>{<br><br>{\mathrm{\rho <br><br>}}_1-{\mathrm{\rho <br><br>}}_2<br><br>}^2,$

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.

2. The RFID tag of claim 1, wherein the tag driver further comprises:

a memory which stores data;

a controller which detects the data from the memory corresponding to the input power, modulates the carrier wave, and generates the reflection power with the carrier wave modulated corresponding to the input power; and

the accumulation mode capacitor which adjusts an impedance of the tag driver by adaptively adjusting the capacitance according to the intensity of a voltage of the reflection power, receives the reflection power from the controller and provides the reflection power to the tag antenna.

3. The RFID tag of claim 2, wherein in the accumulation mode capacitor, the capacitance value increases if the voltage of the reflection power is lower than a threshold voltage, and the capacitance value decreases if the voltage of the reflection power is higher than the threshold voltage.

4. The RFID tag of claim 2, wherein the accumulation mode capacitor comprises at least one varactor connected to an input pad and a ground pad of the RFID antenna.

5. The RFID tag of claim 4, wherein the varactor comprises:

a gate part which receives the voltage of the reflection power;

a source part; and

a drain part which is connected to the source part, and

the gate part which is electrically connected to a connecting line which connects the source part and the drain part.

6. The RFID tag of claim 1, wherein the effective power is an effective isotropic radiation power of the tag antenna, and the minimum power for backscattering is approximately −

70dBm.

7. The RFID tag of claim 1, wherein the impedance of the tag antenna is a complex conjugate of the impedance of the tag driver.

8. A radio frequency identification (RFID) system comprising:

an RFID reader which radiates an input power; and

an RFID tag comprising a tag antenna which receives the input power from the RFID reader and radiates a reflection power including a carrier wave to the RFID reader, and a tag driver which is electrically connected to the tag antenna,

wherein the tag driver comprises;

a memory which stores data;

a controller which detects the data from the memory corresponding to the input power, modulates the carrier wave, and generates the reflection power with the carrier wave modulated corresponding to the input power; and

an accumulation mode capacitor which adjusts an impedance of the tag driver by adaptively adjusting the capacitance according to the intensity of a voltage of the reflection power, and receives the reflection power from the controller and provides the reflection power to the tag antenna, the capacitance of the accumulation mode capacitor being 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;

$P_{\mathrm{bs}}=\frac{P_a}{4}\times <br><br>{<br><br>{\mathrm{\rho <br><br>}}_1-{\mathrm{\rho <br><br>}}_2<br><br>}^2,$

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.