Self tuning RFID tags

• US 8,952,792 B1
• Filed: 01/06/2012
• Issued: 02/10/2015
• Est. Priority Date: 01/07/2011
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Srinivas, Shailendra, Kuhn, Jay, Oliver, Ronald A., Hyde, John D., Diorio, Christopher J.
• Primary Examiner(s): Wu, Daniel
• Assistant Examiner(s): Littlejohn, Jr., Mancil
• Application Number:
  US13/345,654
• Time in Patent Office: 1,131 Days
• Field of Search: 340 101- 106, 3405721-5729, 340/534, 340/5.6, 340/5.65, 340/5.26, 340/5.8, 340/5.2, 340/5.86, 340/645, 340/539, 455/229, 455/73, 455/210, 455/19, 455/343.3, 455/127.5, 455/333, 455/299, 343/852, 343/743, 343/702, 343/795, 363/139
• US Class Current: 340/10.5
• CPC Class Codes: G06K 19/0709 the source being an interrogation field
• CPC Class Codes: G06K 19/0715 the arrangement including means to regulate power transfer to the integrated circuit
• CPC Class Codes: H01Q 1/2208 associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems methods or arrangements for sensing record carriers, e.g. for reading patterns G06K7/00; record carrier for use with machines and with at least a part designed to carry digital markings G06K19/00
• CPC Class Codes: H01Q 1/248 provided with an AC/DC converting device, e.g. rectennas
• CPC Class Codes: H01Q 5/335 at the feed, e.g. for impedance matching
• CPC Class Codes: H03H 7/38 Impedance-matching networks
• CPC Class Codes: H04Q 2213/13095 PIN / Access code, authentication

Abstract

A tuning circuit in an RFID tag may be used to match antenna and integrated circuit (IC) impedances to maximize the efficiency of IC power extraction from an incident RF wave. The tuning circuit, which requires less power to operate than the IC, adjusts a variable impedance to improve the impedance matching between the IC and the tag antenna and thereby increase the IC power extraction efficiency. The IC may begin operating according to a protocol when it extracts sufficient power from the RF wave or when an optimal impedance matching and power transfer is achieved.

Claims

1. A Radio Frequency Identification (RFID) tag, comprising:

an antenna;

a variable impedance; and

an integrated circuit (IC) including a tuning circuit coupled to the variable impedance, the IC requiring a sufficient power to operate according to a protocol (SPOI), the tuning circuit requiring a sufficient power to tune the variable impedance (SPTT), the SPOI greater than the SPTT, wherein the IC is configured to;

extract, before tuning the variable impedance, a first power from an RF wave incident on the antenna greater than the SPTT but less than the SPOI;

tune the variable impedance to increase an efficiency of power extraction;

extract, after tuning the variable impedance, a second power from the RF wave incident on the antenna greater than the SPOI; and

operate according to the protocol after tuning the variable impedance.

2. The tag of claim 1, further including a matching network, wherein at least one of the IC and the matching network includes the variable impedance.

3. The tag of claim 1, wherein the variable impedance includes at least one of a switched capacitor, a variable capacitor, a switched inductor, a variable inductor, a switched transmission line, a variable length transmission line, a switched resistor, and a variable resistor.

4. The tag of claim 1, wherein the IC is further configured to prevent the operation of another IC component while tuning the variable impedance.

5. The tag of claim 1, wherein adjusting the variable impedance includes setting the variable impedance to an initial state.

6. The tag of claim 1, wherein adjusting the variable impedance includes determining an adjustment based on a difference between a current extracted power value and a previous extracted power value.

7. The tag of claim 1, wherein the IC is configured to tune the variable impedance in response to a reader command.

8. The tag of claim 1, wherein the IC uses a measurement of the extracted first power to determine the tuning of the variable impedance.

9. The tag of claim 8, wherein the IC halts the tuning when at least one of the extracted first power decreases and a new impedance value exceeds a impedance tuning range.

10. A Radio Frequency Identification (RFID) integrated circuit (IC) requiring a sufficient power to operate according to a protocol (SPOI), the IC comprising

a variable impedance and

a tuning circuit requiring a sufficient power to tune the variable impedance (SPTT), the SPOI greater than the SPTT, wherein the IC is configured to:

extract, before tuning the variable impedance, a first power from an RF wave incident on an antenna, the first power greater than the SPTT but less than the SPOI;

tune the variable impedance to increase an efficiency of power extraction;

extract, after tuning the variable impedance, a second power from the RF wave incident on the antenna greater than the SPOI; and

operate according to the protocol after tuning the variable impedance.

11. The IC of claim 10, wherein the variable impedance includes at least one of a switched capacitor, a variable capacitor, a switched inductor, a variable inductor, a switched transmission line, a variable length transmission line, a switched resistor, and a variable resistor.

12. The IC of claim 10, wherein the IC is further configured to prevent the operation of another IC component while tuning the variable impedance.

13. The IC of claim 10, wherein the IC is configured to tune adjusting the variable impedance by setting the variable impedance to an initial state.

14. The IC of claim 10, wherein the IC is configured to tune the variable impedance includes by determining an adjustment based on a difference between a current extracted power value and a previous extracted power value.

15. The IC of claim 10, wherein the IC is configured to tune the variable impedance in response to a reader command.

16. A method for tuning a power extraction efficiency of a Radio Frequency Identification (RFID) tag having an antenna, a variable impedance, and an integrated circuit (IC) including a tuning circuit, wherein the IC requires a sufficient power to operate according to a protocol (SPOI), the tuning circuit requires a sufficient power to tune the variable impedance (SPTT), and the SPOI is greater than the SPTT, the method, comprising:

causing the IC to extract, before tuning the variable impedance, a first power from an RF wave incident on the antenna greater than the SPTT but less than the SPOI;

causing the IC to tune the variable impedance to increase the power extraction efficiency;

causing the IC to extract, after tuning the variable impedance, a second power from the RF wave incident on the antenna greater than the SPOI; and

causing the IC to operate according to the protocol after tuning the variable impedance.

17. The method of claim 16, further comprising preventing the operation of another IC component while the IC tunes the variable impedance.

18. The method of claim 16, further comprising setting the variable impedance to an initial state.

19. The method of claim 16, further comprising tuning the variable impedance based on a difference between a current extracted power value and a previous extracted power value.