INTERFERENCE REJECTION IN RFID TAGS

• US 20100182129A1
• Filed: 03/30/2010
• Published: 07/22/2010
• Est. Priority Date: 04/29/2005
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Sundstrom, Kurt E., Hyde, John D.
• Granted Patent: US 8,391,785 B2
• Time in Patent Office: Days
• US Class Current: 340/10.200
• 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 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 while substantially retaining digital pulses longer than the first time duration threshold.

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 first time duration threshold is derived from a clock signal.

4. The circuit of claim 1, wherein

the first time duration threshold is derived in response to the modulated wireless RF input signal.

5. The circuit of claim 1, wherein

the first time duration threshold is derived from one of a data rate and a feature duration associated with the modulated wireless RF input signal.

6. The circuit of claim 5, wherein

the feature duration is a duration of a frame sync tari symbol encoded in the modulated wireless RF input signal.

7. The circuit of claim 1, wherein

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

8. 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.

9. 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 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.

10. The circuit of claim 9, wherein

the digital pulses are at least one of:

low going and high going pulses.

11. The circuit of claim 9, wherein

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

12. The circuit of claim 9, wherein

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

13. The circuit of claim 9, wherein

at least one of the first time duration threshold and the second time duration threshold are derived from one of a data rate and a feature duration associated with the modulated wireless RF input signal.

14. The circuit of claim 9, wherein

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

15. A method for a Radio Frequency Identification (RFID) tag including:

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, 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

substantially removing digital pulses shorter than a first time duration threshold while substantially retaining digital pulses longer than the first time duration threshold.

16. The method of claim 15, wherein

the digital pulses are at least one of:

low going and high going pulses.

17. The method of claim 15, further comprising:

deriving the first time duration threshold from a clock signal.

18. The method of claim 15, further comprising:

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

19. The method of claim 15, further comprising:

deriving the first time duration threshold from one of a data rate and a feature duration associated with the modulated wireless RF input signal.

20. The method of claim 15, further comprising:

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.