Interference rejection in RFID tags

• US 20060244598A1
• Filed: 03/22/2006
• Published: 11/02/2006
• Est. Priority Date: 04/29/2005
• Status: Abandoned Application

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Hyde, John D., Sundstrom, Kurt Eugene
• Application Number:
  US11/386,177
• Publication Number:
  US 20060244598A1
• Time in Patent Office: Days
• US Class Current: 340/572.100
• CPC Class Codes: G06K 19/0707 the arrangement being capable of collecting energy from external energy sources, e.g. thermocouples, vibration, electromagnetic radiation G06K19/0702 takes precedence
• 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

Abstract

RFID tags, tag circuits, and methods are provided that reject at least in part the distortion caused to wireless signals by interference in the environment. When the received RF wave is converted into an unfiltered input (971), a filtered output (972) is generated that does not include an artifact feature deriving from the distortion. The filtered output is used instead of the unfiltered input, which results in tag operation as if there were less interference in the environment, or none at all.

Claims

33. A method for a circuit of an RFID tag, comprising:

deriving an unfiltered input from a wireless signal received by the tag, the wireless signal including distortion due to interference;

generating a filtered output by detecting and removing from the unfiltered input an artifact feature deriving from the distortion; and

performing an operation responsive to the filtered output.

1. A tag circuit for an RFID tag, comprising:

a first circuit operable to derive an unfiltered input responsive to a wireless signal received by the tag, the wireless signal including distortion due to interference;

an interference rejection filtering circuit (IRF) operable to generate a filtered output by detecting and removing from the unfiltered input an artifact feature deriving from the distortion; and

a processor operable to perform an operation responsive to the filtered output.

2. The circuit of claim 1, in which

the first circuit includes a demodulator.

3. The circuit of claim 1, in which

the unfiltered input includes a first number.

4. The circuit of claim 1, in which

the unfiltered input is a first signal.

5. The circuit of claim 1, in which

the filtered output includes a second number.

6. The circuit of claim 1, in which

the filtered output is a second signal.

7. The circuit of claim 1, in which

the IRF includes a first filter portion operable to detect a first feature of the unfiltered input as the artifact feature, if the first feature meets a first criterion.

8. The circuit of claim 7, in which

the filter portion is further operable to include in the filtered output a second feature of the unfiltered input, which does not meet the first criterion.

9. The circuit of claim 7, in which

the filter portion includes a decision block operable to determine whether the first feature meets the first criterion.

10. The circuit of claim 7, in which

one of the IRF and the processing block includes a duration determination block operable to determine a time duration of the first feature, and

the first criterion is that the time duration is less than a low threshold time.

11. The circuit of claim 10, in which

the duration determination block is operable to receive substantially periodic samples;

and

count, during the first feature, an artifact number for the time duration responsive to the received samples, and

the first criterion is met if the artifact number is less than a low number corresponding to the low threshold time.

12. The circuit of claim 11, in which

the IRF further includes a register operable to store a value associated with the low number.

13. The circuit of claim 10, in which

the unfiltered input includes transitions between a high extreme value and a low extreme value,

the feature identifier block is operable to identify at least some of the transitions, and

the first feature is a pattern of two of the identified transitions.

14. The circuit of claim 13, in which

the pattern is two successive transitions.

15. The circuit of claim 13, in which

the pattern is two transitions having the same direction.

16. The circuit of claim 13, in which

the unfiltered input includes input data about the transitions.

17. The circuit of claim 13, in which

the filtered output includes output data about the transitions.

18. The circuit of claim 10, in which

the IRF includes a control portion adapted to adjust the low threshold time.

19. The circuit of claim 18, further comprising:

a memory register operable to store a value associated with the adjusted low threshold time.

20. The circuit of claim 18, in which

the low threshold time is adjusted responsive to a control signal from the control portion.

21. The circuit of claim 18, in which

the low threshold time is adjusted responsive to the unfiltered input.

22. The circuit of claim 18, in which

the low threshold time is adjusted responsive to another wireless signal received from an RFID reader.

23. The circuit of claim 18, in which

the IRF includes:

a second filter portion, the first and second filter portions having different respective low threshold times; and

a multiplexer operable to select an output of one of the first and second filter portions.

24. The circuit of claim 23, further comprising:

a processor for determining a transmission data rate from the wireless signal, and

in which the selection is performed according to the data rate.

25. The circuit of claim 18, in which

the low threshold time is adjusted responsive to an aspect of the filtered output.

26. The circuit of claim 25, in which

the filtered output includes a plurality of packets, and

the aspect is a statistic of a characteristic of the packets.

27. The circuit of claim 25, in which

the filtered output includes a series of packets, and

the aspect is a first expected one of the packets.

28. The circuit of claim 27, in which

the first expected packet is one of:

a preamble, and a first packet in an inventory round.

29. The circuit of claim 27, in which

the IRF is further operable to then identify the first expected packet in the filtered output.

30. The circuit of claim 29, in which

the IRF is further operable to then adjust the low threshold time responsive to a second expected one of the packets.

31. The circuit of claim 30, in which

the IRF is further operable to look up a value associated with the second expected packet.

32. The circuit of claim 30, in which

the low threshold time is adjusted responsive to the second expected packet responsive to the first operative packet being identified.

34. The method of claim 33, in which

the unfiltered input includes a first number.

35. The method of claim 33, in which

the unfiltered input is a first signal.

36. The method of claim 33, in which

the filtered output includes a second number.

37. The method of claim 33, in which

the filtered output is a second signal.

38. The method of claim 33, further comprising:

detecting a first feature of the unfiltered input as the artifact feature if it meets a first criterion.

39. The method of claim 38, in which

a second feature of the unfiltered input, which does not meet the first criterion, is included in the filtered output.

40. The method of claim 38, further comprising:

determining a time duration of the identified first feature, and

in which the first criterion is that the time duration is less than a low threshold time.

41. The method of claim 40, in which

the time duration is determined by counting, during the first feature and responsive to received substantially periodic samples, an artifact number, and

the first criterion is met if the artifact number is less than a low number corresponding to the low threshold time.

42. The method of claim 41, further comprising:

storing a value associated with the low number.

43. The method of claim 40, in which

the unfiltered input includes transitions between a high extreme value and a low extreme value,

the first feature is a pattern of two of the identified transitions.

44. The method of claim 43, in which

the pattern is two successive transitions.

45. The method of claim 43, in which

the pattern is two transitions having the same direction.

46. The method of claim 43, in which

the unfiltered input includes input data about the transitions.

47. The method of claim 43, in which

the filtered output includes output data about the transitions.

48. The method of claim 40, further comprising:

adjusting the low threshold time.

49. The method of claim 48, further comprising:

storing a value associated with the adjusted low threshold time.

50. The method of claim 48, in which

the low threshold time is adjusted responsive to another wireless signal received from an RFID reader.

51. The method of claim 48, in which

the low threshold time is adjusted responsive to an aspect of the unfiltered input.

52. The method of claim 51, further comprising:

determining a transmission data rate from the wireless signal, and

in which the selection is performed according to the data rate.

53. The method of claim 48, in which

the low threshold time is adjusted responsive to an aspect of the filtered output.

54. The method of claim 53, in which

the filtered output includes a plurality of packets, and

the aspect is a statistic of a characteristic of the packets.

55. The method of claim 53, in which

the filtered output includes a series of packets, and

the aspect is a first expected one of the packets.

56. The method of claim 55, in which

the first expected packet is one of:

a preamble, and a first packet in an inventory round.

57. The method of claim 55, further comprising:

then identifying the first expected packet in the filtered output.

58. The method of claim 57, further comprising:

then adjusting the low threshold time responsive to a second expected one of the packets.

59. The method of claims 58, further comprising:

looking up a value associated with the second expected packet.

60. The method of claim 59, in which

the low threshold time is adjusted responsive to the second expected packet responsive to the first operative packet being identified.

51-1. The method of claim 48, in which

the low threshold time is adjusted by selecting one of a plurality of filters having different respective low threshold times.

61. An RFID tag, comprising:

antenna means operable to receive a wireless signal that includes distortion due to interference;

deriving means for deriving an unfiltered input from the wireless signal;

generating means for generating a filtered output by detecting and removing from the unfiltered input an artifact feature deriving from the distortion; and

processor means for performing an operation responsive to the filtered output.

62. The tag of claim 61, in which

the unfiltered input includes a first number.

63. The tag of claim 61, in which

the unfiltered input is a first signal.

64. The tag of claim 61, further comprising:

detecting means for detecting a first feature of the unfiltered input as the artifact feature if it meets a first criterion.

65. The tag of claim 64, in which

a second feature of the unfiltered input, which does not meet the first criterion, is included in the filtered output.

66. The tag of claim 65, further comprising:

duration determination means for determining a time duration of the first feature, and

in which the first criterion is that the time duration is less than a low threshold time.

67. The tag of claim 66, in which

the time duration is determined by counting, during the first feature and responsive to received substantially periodic samples, an artifact number, and

the first criterion is met if the artifact number is less than a low number corresponding to the low threshold time.

68. The tag of claim 67, further comprising:

storing means for storing a value associated with the low number.

69. The tag of claim 67 in which

the unfiltered input includes transitions between a high extreme value and a low extreme value,

the first feature is a pattern of two of the identified transitions.

70. The tag of claim 69, in which

the pattern is two successive transitions.

71. The tag of claim 70, in which

the unfiltered input includes input data about the transitions.

72. The tag of claim 67, further comprising:

adjusting means for adjusting the low threshold time.

73. The tag of claim 72, in which

the low threshold time is adjusted responsive to another wireless signal received from an RFID reader.

74. The tag of claim 72, in which

the low threshold time is adjusted responsive to an aspect of the unfiltered input.

75. The tag of claim 72, in which

the low threshold time is adjusted responsive to an aspect of the filtered output.