Inductively tunable antenna for a radio frequency identification tag

• US 6,480,110 B2
• Filed: 12/01/2000
• Issued: 11/12/2002
• Est. Priority Date: 12/01/2000
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Lee, Youbok, Furey, Lee, St. Amand, Roger
• Primary Examiner(s): Lee, Benjamin C.
• Assistant Examiner(s): NGUYEN, PHUNG
• Application Number:
  US09/728,190
• Publication Number:
  US 20020097153A1
• Time in Patent Office: 711 Days
• Field of Search: 340/572.5, 340/572, 340/572.4, 343/741, 343/818, 455/13.3
• US Class Current: 340/572.5
• CPC Class Codes: G06K 19/0672 with resonating marks
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• 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: H01F 2021/125 Printed variable inductor with taps, e.g. for VCO
• CPC Class Codes: H01F 5/003 Printed circuit coils
• CPC Class Codes: H01Q 1/2241 used in or for vehicle tyres

Abstract

A radio frequency identification tag having a step-tunable inductor for tuning a parallel resonant antenna circuit of the radio frequency identification tag to a desired frequency. The step-tunable inductor comprises a plurality of branches in which each branch is adapted for adjusting the step-tunable inductor to a desired inductance value for resonating the parallel antenna circuit to a carrier frequency of a tag interrogator/reader.

Claims

1. A radio frequency identification tag, comprising:

an insulated substrate having a surface;

a parallel resonant antenna circuit disposed on the surface of said substrate, said parallel resonant antenna circuit having a step-tunable inductor comprising a spiral coil adapted for tuning said parallel resonant antenna circuit to a desired frequency, wherein said step-tunable inductor has trimming branches disposed on the surface of said substrate and entirely inside of said spiral coil, wherein said trimming branches are adapted for adjusting the inductance of said step-tunable inductor; and

a semiconductor integrated circuit having electronic logic circuits for storing, receiving and transmitting data, said semiconductor integrated circuit being disposed on the surface of said substrate and connected to said parallel resonant antenna circuit.

2. The radio frequency identification tag of claim 1, wherein said step-tunable inductor is a spiral coil disposed on the surface of said substrate.

3. The radio frequency identification tag of claim 1, wherein said trimming branches are controlled by transistors.

4. The radio frequency identification tag of claim 3, wherein said transistors are controlled with fuse links.

5. The radio frequency identification tag of claim 3, wherein said transistors are controlled with a frequency selection circuit.

6. The radio frequency identification tag of claim 5, wherein said frequency selection circuit is a microcontroller.

7. The radio frequency identification tag of claim 1. wherein said trimming branches are controlled by fuse links.

8. The radio frequency identification tag of claim 7 wherein said fuse links are opened with a current.

9. The radio frequency identification tag of claim 7, wherein said fuse links are opened with a voltage.

10. The radio frequency identification tag device of claim 1, wherein said step-tunable inductor comprises a spiral coil having a plurality of coil turns.

11. The radio frequency identification tag device of claim 10, wherein all but one of said plurality of trimming branches are disconnected so as to adjust the inductance of said step- tunable inductor.

12. The radio frequency identification tag of claim 11, wherein each of said plurality of trimming branches form a different length inner coil turn of the plurality of coil turns of said spiral coil.

13. The radio frequency identification tag of claim 1, wherein material for said substrate is selected from the group consisting of PET, mylar, paper, plastic, silicon, kapton, ceramic, polyimide and polyvinylchloride (PVC).

14. The radio frequency identification tag of claim 1, wherein material for said step- tunable inductor is selected from the group consisting of copper, aluminum, gold, plated metal, and electrically conductive organic and inorganic materials.

15. The frequency identification tag of claim 1. wherein said step-tunable inductor has a plurality of fuse links, each of the plurality of fuse links in parallel with a turn of said step-tunable inductor wherein opening a one of the plurality of fuse links increases said step-tunable inductor inductance.

16. The frequency identification tag of claim 1, wherein said step-tunable inductor has a plurality of transistors, each of the plurality of transistor in parallel with a turn of said step-tunable inductor wherein turning off a one of the plurality of transistors increases said step-tunable inductor inductance.

17. A radio frequency identification (RFID) tag system, comprising:

a radio frequency identification (RFID) tag comprising an insulated substrate having a surface, a parallel resonant antenna circuit disposed on the surface of said substrate, said parallel resonant antenna circuit having a step-tunable inductor comprising a spiral coil adapted for tuning said parallel resonant antenna circuit to a desired frequency, wherein said step- tunable inductor has trimming branches disposed on the surface of said substrate and entirely inside of said spiral coil, wherein said trimming branches are adapted for adjusting the inductance of said step-tunable inductor, and a simiconductor integrated circuit having electronic logic circuits for storing, receiving and transmitting data, said semiconductor integrated circuit being disposed on the surface of said substrate and connected to said parallel resonant antenna circuit;

a radio frequency interrogator for generating a radio frequency signal at the desired frequency which said parallel resonant antenna circuit is tuned; and

an RFID tag reader connected to said radio frequency interrogator, said RFID tag reader detecting data signals from said RFID tag.

18. The radio frequency identification tag system of claim 17, wherein said step- tunable inductor is a spiral coil disposed on the surface of said substrate.

19. The radio frequency identification tag system of claim 17, wherein said step- tunable inductor comprises a spiral coil having a plurality of coil turns and a plurality of trimming branches inside of said spiral coil, wherein said plurality of trimming branches are adapted for adjusting the inductance of said step-tunable inductor.

20. The radio frequency identification tag system of claim 19, wherein all but one of said plurality of trimming branches are disconnected so as to adjust the inductance of said step- tunable inductor.

21. The radio frequency identification tag of claim 20, wherein each of said plurality of trimming branches form a different length inner coil turn of the plurality of coil turns of said spriral coil.

22. A method for step-tuning an inductor in a parallel resonant antenna circuit of a radio frequency identification (RFID) tag, said method comprising the steps of:

providing an insulated substrate having a surface;

providing a parallel resonant antenna circuit disposed on the surface of said substrate, said parallel resonant antenna circuit having a step-tunable inductor comprising a spiral coil having a plurality of trimming branches entirely inside of said spiral coil and disposed on the surface of said substrate;

providing a semiconductor integrated circuit having electronic logic circuits for storing, receiving and transmitting data, said semiconductor integrated circuit being disposed on the surface of said substrate and connected to said parallel resonant antenna circuit; and

disconnecting all but one of said plurality of trimming branches so as to adjust the inductance of said step-tunable inductor, thereby changing a resonant frequency of said parallel resonant antenna circuit.

23. The method of claim 22, wherein the step of disconnecting is done by cutting with a laser.

24. The method of claim 22, wherein the step of disconnecting is done by ablation.

25. The method of claim 22, wherein the step of disconnecting is done by mechanically cutting.

26. The method of claim 22, wherein the step of disconnecting all but one of said plurality of trimming branches adjusts the length of an inner coil turn of the spiral coil of said step-tunable inductor.

27. The method of claim 22, wherein the step of disconnecting is done by opening fuse links.

28. The method of claim 27, wherein said fuse links are opened with a current.

29. The method of claim 27, wherein said fuse links are opened with a voltage.

30. The method of claim 29, wherein the step of disconnecting is done by controlling transistors.

31. The method of claim 30, wherein said transistors are controlled with fuse links.

32. The method of claim 30, wherein said transistors are controlled with a frequency selection circuit.

33. The method of claim 32, wherein said frequency selection circuit is a microcontroller.