SYSTEMS AND METHODS FOR AN RF NULLING SCHEME IN RFID

• US 20070060075A1
• Filed: 09/14/2006
• Published: 03/15/2007
• Est. Priority Date: 09/14/2005
• Status: Active Grant

• Current Assignee: Smartrac Technology Fletcher, Inc. (Avery Dennison Corporation)
• Original Assignee: Neology Incorporated (OEP Technologie BV)
• Inventors: Mikuteit, Eric
• Granted Patent: US 7,787,837 B2
• Time in Patent Office: Days
• US Class Current: 455/127.200
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

Systems and methods for an RF nulling scheme are provided. An RF nulling scheme can minimize the level of unwanted RF signal reflections entering the receiver without attenuating the desired signal response from an RFID tag. In one aspect of the RF nulling scheme a synthesizer signal can be split between a main path and a nulling path. In the nulling path the signal from the splitter can be routed through an electronically variable phase shifter and variable gain amplifier to create a nulling signal. The nulling signal can cancel the unwanted reflected signal. The phase or amplitude of the nulling signal can then be adjusted to improve cancellation as necessary.

Claims

1. An RFID receiver comprising:

a nulling path circuit configured to create a phase shifted, amplitude controlled nulling signal, the nulling path circuit comprising;

a phase shifter configured to control the phase of a nulling signal, and

a variable gain amplifier coupled with the phase shifter, the variable amplifier configured to control the amplitude of the nulling signal;

an RF coupler coupled to the phase shifter and the variable gain amplifier, the RF coupler configured to combine the nulling signal and a receive signal, the receive signal comprising an undesired signal, in such a manner so as to provide at least partial cancellation of the undesired signal;

an RF detector coupled to the RF coupler, the RF detector configured to detect whether there is sufficient cancellation of the undesired signal and provide feedback; and

a processor coupled to the phase shifter, the variable gain amplifier, and the detector, the processor configured to control the phase shifter and the variable gain amplifier based on the feedback provided.

2. The RFID receiver of claim 1, wherein the undesired signal comprises leakage from a transmission path to a receive path.

3. The RFID receiver of claim 1, wherein the undesired signal comprises unintended reflections from an external source.

4. The RFID receiver of claim 1, wherein the undesired signal comprises both leakage from a transmission path to a receive path and unintended reflections from an external source.

5. The RFID receiver of claim 1, further comprising a transmit frequency synthesizer coupled to the phase shifter and the variable gain amplifier, the frequency synthesizer configured to provide a transmit signal.

6. The RFID receiver of claim 5, further comprising an RF power divider coupled to the frequency synthesizer, the phase shifter, and the variable gain amplifier, the RF power divider configured to split the transmit signal into a main path signal and the nulling signal.

7. The RFID receiver of claim 1, further comprising a power amplifier coupled to the RF power divider and configured to control the amplitude of the main path signal.

8. The RFID receiver of claim 1, further comprising a circulator coupled to an RF coupler, a phase shifter, and a variable gain amplifier, the circulator configured to couple the main path signal to an antenna.

9. The RFID receiver of claim 1, wherein the nulling path circuit comprises a single device.

10. The RFID receiver of claim 1, wherein the RFID receiver is included in an RFID reader.

11. The RFID receiver of claim 1, wherein the processor controls the phase shifter and the variable gain amplifier such that sufficient cancellation of the undesired signal is provide for multiple transmit frequencies.

12. The RFID receiver of claim 1, wherein the processor controls the phase shifter and the variable gain amplifier such that sufficient cancellation of the undesired signal is provide for multiple antenna ports.

13. A method of receiving a signal from an RFID tag comprising:

controlling the phase of an RF signal;

controlling the amplitude of the RF signal, thereby creating a phase shifted, amplitude controlled nulling signal;

coupling the nulling signal with a receive RF signal, the receive RF signal comprising an undesired signal, thereby providing at least partial cancellation of the undesired signal;

sampling the combined received RF signal and nulling signal to determine whether the undesired signal has been sufficiently cancelled;

generating feedback indicating whether the undesired signal has been sufficiently cancelled; and

adjusting at least one of the phase or amplitude of the RF signal based on the feedback.

14. The method of claim 13, further comprising providing the transmit frequency RF signal using a frequency synthesizer.

15. The method of claim 13, further comprising splitting the transmit frequency RF signal into a main path signal and a nulling path signal.

16. The method of claim 13, further comprising controlling the amplitude of the main path signal.

17. The method of claim 13, further comprising routing an amplitude controlled main path signal to an antenna.

18. The method of claim 13, wherein the steps are continually repeated.

19. The method of claim 13, further comprising controlling the phase and the amplitude of a nulling signal such that sufficient cancellation of the undesired signal is provide for multiple transmit frequencies.

20. The method of claim 13, further comprising controlling the phase and the amplitude of a nulling signal such that sufficient cancellation of the undesired signal is provide for multiple antenna ports.

21. An RFID system, comprising

an RFID receiver, the RFID receiver comprising:

a nulling path circuit configured to create a phase shifted, amplitude controlled nulling signal, the nulling path circuit comprising;

a phase shifter configured to control the phase of a nulling path input signal, and

a variable gain amplifier coupled with the phase shifter, the variable amplifier configured to control the amplitude of the nulling signal;

an RF coupler coupled to the phase shifter and the variable gain amplifier, the RF coupler configured to combine the nulling signal and a receive signal, the receive RF signal comprising an undesired signal, in such a manner as to provide at least partial cancellation of the undesired signal;

an RF detector coupled to the RF coupler, the RF detector configured to detect whether there is sufficient cancellation of the undesired signal and provide feedback; and

a processor coupled to the phase shifter, the variable gain amplifier, and the detector, the processor configured to control the phase shifter and the variable amplifier based on the feedback provided; and

an RFID tag configured to receive an RF signal and backscatter modulate the RF signal with information.

22. The RFID system of claim 21, wherein the RFID receiver further comprises a transmit frequency synthesizer coupled to the phase shifter and the variable gain amplifier, the frequency synthesizer configured to provide a transmit signal.

23. The RFID system of claim 21, wherein the RFID receiver further comprises an RF power divider coupled to the frequency synthesizer, the phase shifter, and the variable gain amplifier, the RF power divider configured to split the transmit signal into a main path signal and the nulling signal.

24. The RFID system of claim 21, wherein the RFID receiver further comprises a power amplifier coupled to the RF power divider and configured to control the amplitude of the main path signal.

25. The RFID system of claim 21, wherein the RFID receiver further comprises a circulator coupled to an RF coupler, a phase shifter, and a variable gain amplifier, the circulator configured to couple the main path signal to an antenna.

26. The RFID system of claim 21, wherein the RFID receiver further comprises the nulling path circuit implemented in a single device.

27. The RFID system of claim 21, wherein the RFID receiver is included in an RFID reader.

28. The RFID system of claim 21, wherein the RFID receiver processor controls the phase shifter and the variable gain amplifier such that sufficient cancellation of the undesired signal is provide for multiple transmit frequencies.

29. The RFID system of claim 21, wherein the RFID receiver processor controls the phase shifter and the variable gain amplifier such that sufficient cancellation of the undesired signal is provide for multiple antenna ports.