Interference rejection in RFID tags

• US 8,391,785 B2
• Filed: 03/30/2010
• Issued: 03/05/2013
• Est. Priority Date: 04/29/2005
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Hyde, John D., Sundstrom, Kurt E.
• Primary Examiner(s): HSIEH, PING Y
• Application Number:
  US12/749,648
• Publication Number:
  US 20100182129A1
• Time in Patent Office: 1,071 Days
• Field of Search: 455/39, 455/41.1, 455/41.2, 455/41.3, 455/42, 455/43, 455/67.13, 340/10.1, 340/10.52, 340/10.34, 340/572.1
• US Class Current: 455/41.1
• 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
• CPC Class Codes: G06K 7/10029 the collision being resolved in the time domain, e.g. using binary tree search or RFID responses allocated to a random time slot

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

1. A Radio Frequency Identification (RFID) tag circuit including:

a demodulator adapted to receive a modulated wireless RF input signal from an RFID reader and to derive a first digital output signal responsive to the modulated wireless RF input signal, wherein the first digital output signal comprises a sequence of digital pulses; and

an interference rejection circuit adapted to receive the first digital output signal and to derive a second digital output signal responsive to the first digital output by substantially removing digital pulses shorter than a time duration threshold while substantially retaining digital pulses longer than the time duration threshold,

wherein the time duration threshold is determined from one of a frame-sync tari symbol encoded in the modulated wireless RF input signal, a data rate associated with the modulated wireless RF input signal, and a statistic of a characteristic of a received data packet.

2. The circuit of claim 1, wherein

the digital pulses are at least one of:

low going and high going pulses.

3. The circuit of claim 1, wherein

the time duration threshold is derived from a clock signal.

4. The circuit of claim 1, wherein

the time duration threshold is generated responsive to the modulated wireless RF input signal.

5. The circuit of claim 1, wherein

the time duration threshold is derived from another modulated wireless RF input signal received from the RFID reader.

6. The circuit of claim 1, wherein

the interference rejection circuit is at least partially integrated into one of the demodulator and a processor block of the RFID circuit.

7. The circuit of claim 1, wherein

the time duration threshold is determined based on one of a statistic of a characteristic of a received data packet or a data rate of a received data packet.

8. A Radio Frequency Identification (RFID) tag circuit including:

a demodulator adapted to receive a modulated wireless RF input signal from an RFID reader and to derive a first digital output signal responsive to the modulated wireless RF input signal, wherein the first digital output signal comprises a sequence of digital pulses; and

an interference rejection circuit adapted to receive the first digital output signal and to derive a second digital output signal responsive to the first digital output by substantially removing digital pulses shorter than a first time duration threshold and substantially removing digital pulses longer than a second time duration threshold while substantially retaining digital pulses that are longer than the first time duration threshold and shorter than the second time duration threshold,

wherein at least one of the first time duration threshold and the second time duration threshold is derived from one of a data rate associated with the modulated wireless RF input signal and a frame-sync tari symbol encoded in the modulated wireless RF input signal.

9. The circuit of claim 8, wherein

the digital pulses are at least one of:

low going and high going pulses.

10. The circuit of claim 8, wherein

at least one of the first time duration threshold and the second time duration threshold is derived from a clock signal.

11. The circuit of claim 8, wherein

at least one of the first time duration threshold and the second time duration threshold is generated responsive to the modulated wireless RF input signal.

12. The circuit of claim 8, wherein

the interference rejection circuit is at least partially integrated into one of the demodulator and a processor block of the RFID circuit.

13. The circuit of claim 8, wherein

at least one of the first time duration threshold and the second time duration threshold is derived from another modulated wireless RF input signal received from the RFID reader.

14. A method for a Radio Frequency Identification (RFID) tag comprising:

receiving a modulated wireless RF input signal from an RFID reader at a demodulator of the RFID tag;

deriving a first digital output signal responsive to the modulated wireless RF input signal at the demodulator of the RFID tag, wherein the first digital output signal comprises a sequence of digital pulses;

deriving a second digital output signal responsive to the first digital output at an interference rejection circuit of the RFID tag by receiving the first digital output signal and substantially removing digital pulses shorter than a first time duration threshold while substantially retaining digital pulses longer than the first time duration threshold,

wherein at least one of the first time duration threshold and the second time duration threshold is determined from one of a frame-sync tari symbol encoded in the modulated wireless RF input signal, a data rate associated with the modulated wireless RF input signal, and a statistic of a characteristic of a received data packet.

15. The method of claim 14, wherein

the digital pulses are at least one of:

low going and high going pulses.

16. The method of claim 14, further comprising:

deriving at least one of the first time duration threshold and the second time duration threshold from a clock signal.

17. The method of claim 14, further comprising:

generating at least one of the first time duration threshold and the second time duration threshold in response to the modulated wireless RF input signal and another modulated wireless RF input signal from the RFID reader.

18. The method of claim 14, further comprising:

further deriving the second digital output signal by substantially removing digital pulses longer than a second time duration threshold while substantially retaining digital pulses that are shorter than the second time duration threshold and longer than the first time threshold.