Phase shifters, interrogators, methods of shifting a phase angle of a signal, and methods of operating an interrogator

1. A method for minimizing a transmitted continuous-wave (CW) signal that appears within a received backscatter signal, comprising:

adjusting an amplitude of a local CW signal using a variable attenuator to create an amplitude-adjusted local signal, wherein the local CW signal corresponds to the transmitted CW signal;

adjusting a phase of the amplitude-adjusted local signal using a phase shifter to create an adjusted local signal;

computing an amplitude control signal based upon an amplitude of the adjusted local signal and an amplitude of the received backscatter signal;

controlling the variable attenuator using the amplitude control signal;

summing the adjusted local signal and the received backscatter signal to create a summed signal; and

providing the summed signal to processing circuitry.

2. The method of claim 1 , further comprising:

amplifying the summed signal in a low noise amplifier (LNA) before providing the summed signal to the processing circuitry.

3. The method of claim 1 , further comprising:

providing a summed signal amplitude measurement to a phase adjuster;

receiving, at the phase adjuster, a signal from an amplitude adjuster indicating that the amplitudes of the adjusted local signal and the amplitude of the received backscatter signal have been matched;

selecting, at the phase adjuster, a selected phase shift for the amplitude-adjusted local signal; and

providing a phase control signal to the phase shifter to implement a selected phase shift.

4. The method of claim 1 , wherein the received backscatter signal comprises a received carrier component and received side band components.

5. The method of claim 4 , wherein the side band components are at locations +/−600 kHz of the carrier component.

6. The method of claim 4 , wherein the transmitted CW signal comprises a transmitted carrier component and transmitted side band components.

7. The method of claim 6 , wherein the summed signal comprises a summed carrier component and summed side band components.

8. The method of claim 7 , wherein an amplitude of the summed side band components is approximately the same as an amplitude of the received side band components.

9. The method of claim 7 , wherein an amplitude of the summed carrier component is approximately 20 dBm less than an amplitude of the received carrier component.

10. A method for minimizing transmitted signal bleed-through in a radio frequency identification (RFID) interrogator, comprising:

providing a local continuous-wave (CW) signal to a variable attenuator;

providing an amplitude-adjusted local CW signal from the variable attenuator to a phase shifter;

providing an adjusted local CW signal from the phase shifter to a first amplitude detector;

providing a first amplitude signal from the first amplitude detector to an amplitude adjuster;

providing a return link communication from an RFID tag to a second amplitude detector;

providing a second amplitude signal from the second amplitude detector to the amplitude adjuster;

comparing, in the amplitude adjuster, an amplitude of the adjusted local CW signal and an amplitude of the return link communication;

providing an amplitude control signal from the amplitude adjuster to the variable attenuator;

providing the adjusted local CW signal to a first coupler;

providing the return link communication to the first coupler;

summing, in the first coupler, the adjusted local CW signal and the return link communication to create a summed signal;

providing the summed signal to a low noise amplifier (LNA);

providing the summed signal to a third amplitude detector;

providing a third amplitude signal from the third amplitude detector to a phase adjuster;

providing a signal from the amplitude adjuster to the phase adjuster indicating that the amplitudes of the adjusted local CW signal and the return link communication have been matched;

selecting, at the phase adjuster, a selected phase shift for the amplitude-adjusted local CW signal; and

providing a phase control signal from the phase adjuster to the phase shifter to implement the selected phase shift.

11. The method of claim 10 , wherein the local CW signal is transmitted by the RFID interrogator during a backscatter mode of operation.

12. The method of claim 10 , wherein the variable attenuator is a voltage-controlled attenuator.

13. The method of claim 10 , wherein the variable attenuator is configured to adjust an amplitude of the local CW signal in response to an external amplitude control signal.

14. The method of claim 10 , wherein an external control signal drives the variable attenuator to equalize the amplitudes of the adjusted local CW signal and the return link communication.

15. The method of claim 10 , wherein the phase shifter is a 360 degree phase shifter.

16. The method of claim 10 , wherein the phase shifter is configured to provide a phase shift to the amplitude-adjusted local CW signal, and wherein the phase shifter is controlled by an external phase control signal.

17. The method of claim 10 , wherein the adjusted local CW signal has an adjusted amplitude and an adjusted phase.

18. The method of claim 10 , further comprising:

providing the adjusted local CW signal to a power divider, wherein the power divider provides the adjusted local CW signal to both the first amplitude detector and the first coupler.

19. The method of claim 10 , wherein the return link communication is received from an RFID tag.

20. The method of claim 10 , wherein the return link communication is a modulated continuous-wave signal from an RFID tag.

21. The method of claim 20 , wherein a modulated continuous-wave signal is generated by the RFID tag using a backscatter mode of operation.

22. The method of claim 10 , wherein the amplitude adjuster has a feedback amplifier configuration.

23. The method of claim 10 , wherein the summed signal has an amplitude that is less than an amplitude of the return link communication.

24. The method of claim 10 , further comprising:

applying an output of the LNA to processing circuitry.

25. The method of claim 10 , wherein selecting a phase shift is accomplished by searching across 360 degrees of possible phase adjustments to detect a phase adjustment for the local CW signal that provides a maximum reduction of an amplitude of the return link communication at a CW signal frequency.

26. The method of claim 10 , further comprising:

continuously monitoring, at the phase adjuster, an amplitude of the summed signal; and

providing adjustment control signals from the phase adjuster to the phase shifter to minimize an amplitude of a CW signal within the summed signal.