Interdigit AC coupling for RFID tags

• US 7,564,356 B1
• Filed: 10/06/2006
• Issued: 07/21/2009
• Est. Priority Date: 10/06/2006
• Status: Active Grant

• Current Assignee: Amtech Systems LLC (Roper Technologies, Inc.)
• Original Assignee: TC License Limited
• Inventors: Youn, Tai Won
• Primary Examiner(s): Nguyen; Hung T.
• Application Number:
  US11/543,866
• Time in Patent Office: 1,019 Days
• Field of Search: 340/572.7, 340/572.1, 340/572.8, 340/928, 340/10.1, 340/10.3, 340/825.69, 340/825.72, 343/700, 343/711, 343/789, 343/880, 235/492, 705/13
• US Class Current: 340/572.1
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: G06K 19/07758 arrangements for adhering the record carrier to further objects or living beings, functioning as an identification tag

Abstract

A radio frequency identification (RFID) tag to be attached to an object to identify the object or a characteristic or feature thereof from data stored in the tag accessible by an RFID reader includes an application-specific integrated circuit (ASIC), configured to process signals from the RFID reader and return signals related to the stored data, an interdigit AC coupling circuit, in communication with the ASIC, a matching circuit, in communication with the interdigit AC coupling circuit and an antenna, in communication with the matching circuit, configured to receive signals from the RFID reader and transmit the signals related to the stored data. The interdigit AC coupling circuit and the matching circuit provide an AC coupling and a matching impedance between the ASIC and the antenna respectively.

Claims

1. A radio frequency identification (RFID) tag to be attached to an object to identify the object or a characteristic or feature thereof from data stored in the tag accessible by an RFID reader, said RFID tag comprising:

an application-specific integrated circuit (ASIC), configured to process signals from the RFID reader and return signals related to the stored data;

an interdigit AC coupling circuit, in communication with the ASIC;

a matching circuit, in communication with the interdigit AC coupling circuit; and

an antenna, in communication with the matching circuit, configured to receive signals from the RFID reader and transmit the signals related to the stored data;

wherein the interdigit AC coupling circuit and the matching circuit provide an AC coupling and a matching impedance between the ASIC and the antenna respectively; and

wherein the interdigit AC coupling comprises a number of pairs of interdigit fingers with a coupling gap between the pairs of interdigit fingers and wherein the number of pairs of interdigit fingers and the coupling gap are selected so that the interdigit AC coupling circuit and the matching circuit provide a matching impedance to an impedance of the antenna.

2. The RFID tag of claim 1, wherein the interdigit AC coupling circuit, the matching circuit and the antenna are fabricated from a single layer.

3. The RFID tag of claim 2, wherein the RFID tag further comprises a substrate layer and the single layer is formed on the substrate layer.

4. The RFID tag of claim 3, wherein said substrate layer is a sticker for self-adhesion to the object.

5. The RFID tag of claim 3, wherein said substrate layer is a flexible layer.

6. The RFID tag of claim 2, wherein the interdigit AC coupling circuit, the matching circuit and the antenna are formed from copper.

7. The RFID tag of claim 2, wherein the interdigit AC coupling circuit, the matching circuit and the antenna are formed from conductive ink.

8. The RFID tag of claim 1, wherein said tag is passive.

9. The RFID tag of claim 1, wherein the ASIC, the interdigit AC coupling circuit, the matching circuit and the antenna are encompassed within a coating for protection against damage from ambient environment.

10. The RFID tag of claim 1, configured to be applied wherein said object is a vehicle and said surface is the windshield of the vehicle, for RF communication of said tag with an RFID reader in the vicinity of said vehicle.

11. The RFID tag of claim 1, wherein an impedance magnitude of the interdigit AC coupling circuit approximately 5 ohms and an operating impedance magnitude is approximately 400 ohms at operating frequencies.

12. A method of enabling a vehicle to be detected automatically as being authorized for passage through a lane equipped with an RFID reader, comprising the step of:

making available to the vehicle an RFID tag in the form of a planar compact sticker that incorporates a storage medium programmed with authorization data that identifies the vehicle as being permitted to pass through said lane without stopping, said sticker further comprising an application-specific integrated circuit (ASIC), configured to process signals from the RFID reader and return signals related to the stored data, an interdigit AC coupling circuit, in communication with the ASIC, a matching circuit, in communication with the interdigit AC coupling circuit and an antenna, in communication with the matching circuit, configured to receive signals from the RFID reader and transmit the signals related to the stored data, and wherein the interdigit AC coupling circuit and the matching circuit provide an AC coupling and a matching impedance between the ASIC and the antenna respectively.

13. The method according to claim 12, including the step of affixing said sticker to the windshield of the vehicle.

14. The method according to claim 12, wherein said storage medium is programmed with authorization data that uniquely identifies the vehicle as being permitted to pass through said lane.

15. The method according to claim 12, wherein said lane is for vehicle passage to or from a parking facility.

16. The method according to claim 15, wherein said lane is a payment collection lane for automatic debiting of payment due with each passage of the vehicle therethrough.

17. The method according to claim 15, wherein said lane is a toll collection lane for automatic on-the-fly roadway toll collection with each passage of the vehicle therethrough.

18. A method of making a radio frequency identification (RFID) tag to be attached to an object to identify the object or a characteristic or feature thereof from data stored in the tag accessible by an RFID reader, the method comprising the steps of:

providing a substrate layer;

forming an interdigit AC coupling circuit, a matching circuit and an antenna from a single layer on the substrate layer; and

mounting an application-specific integrated circuit (ASIC), configured to process signals from the RFID reader and return signals related to the stored data;

wherein the interdigit AC coupling circuit is in communication with the ASIC, the matching circuit is in communication with the interdigit AC coupling circuit and the antenna is in communication with the matching circuit, where the antenna is configured to receive signals from the RFID reader and transmit the signals related to the stored data and wherein the interdigit AC coupling circuit and the matching circuit provide an AC coupling and a matching impedance between the ASIC and the antenna respectively.

19. The method of claim 18, wherein the step of providing the substrate layer comprises providing a sticker layer for self-adhesion to the object.

20. The method of claim 18, wherein the step of forming the interdigit AC coupling circuit, the matching circuit and the antenna comprises forming the interdigit AC coupling circuit, the matching circuit and the antenna from one of copper and conductive ink.

21. A radio frequency identification (RFID) tag to be attached to an object to identify the object or a characteristic or feature thereof from data stored in the tag accessible by an RFID reader, the RFID tag having an application-specific integrated circuit (ASIC) and an antenna, wherein:

a interdigit AC coupling circuit and a matching circuit provide an AC coupling and a matching impedance between the ASIC and the antenna respectively; and

wherein the interdigit AC coupling comprises a number of pairs of interdigit fingers with a coupling gap between the Pairs of interdigit fingers and wherein the number of pairs of interdigit fingers and the coupling gap are selected so that the interdigit AC coupling circuit and the matching circuit provide a matching impedance to an impedance of the antenna.

22. The RFID tag of claim 21, wherein the interdigit AC coupling circuit, the matching circuit and the antenna are fabricated from a single layer.

23. The RFID tag of claim 22, wherein the RFID tag further comprises a substrate layer and the single layer is formed on the substrate layer.

24. The RFID tag of claim 23, wherein said substrate layer is a sticker for self-adhesion to the object.

25. The RFID tag of claim 23, wherein said substrate layer is a flexible layer.

26. The RFID tag of claim 22, wherein the interdigit AC coupling circuit, the matching circuit and the antenna are formed from copper.

27. The RFID tag of claim 22, wherein the interdigit AC coupling circuit, the matching circuit and the antenna are formed from conductive ink.

28. The RFID tag of claim 21, wherein said tag is passive.

29. The RFID tag of claim 21, wherein the ASIC, the interdigit AC coupling circuit, the matching circuit and the antenna are encompassed within a coating for protection against damage from ambient environment.

30. The RFID tag of claim 21, configured to be applied wherein said object is a vehicle and said surface is the windshield of the vehicle, for RF communication of said tag with an RFID reader in the vicinity of said vehicle.

31. The RFID tag of claim 21, wherein an impedance magnitude of the interdigit AC coupling circuit approximately 5 ohms and an operating impedance magnitude is approximately 400 ohms at operating frequencies.