Method and apparatus for reducing carrier leakage

• US 9,136,989 B2
• Filed: 10/10/2013
• Issued: 09/15/2015
• Est. Priority Date: 10/10/2013
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola Solutions, Inc.
• Inventors: Drees, Dennis M., Hoon, Bryan A.
• Primary Examiner(s): Nguyen, Lee
• Application Number:
  US14/050,934
• Publication Number:
  US 20150103948A1
• Time in Patent Office: 705 Days
• Field of Search: 455/114.2, 455/126
• US Class Current: 1/1
• CPC Class Codes: H04L 1/206 for modulated signals
• CPC Class Codes: H04L 27/14 Demodulator circuits; Receiver circuits

Abstract

In an embodiment, an apparatus comprises an in-phase-quadrature (IQ) signal amplifier having an IQ baseband input, an IQ mixer input connected to the IQ signal amplifier, a carrier leakage detector connected to outputs of the IQ mixer, and a carrier-null offset signal generator connected to the carrier leakage detector. The IQ mixer is configured to be driven by an IQ carrier signal. The carrier leakage detector is configured to output an in-phase leakage level measurement and a quadrature leakage level measurement in the absence of an IQ baseband signal at the IQ baseband input. The carrier-null offset signal generator is configured to (i) inject an in-phase carrier-null offset signal based on the in-phase leakage level measurement and (ii) inject a quadrature carrier-null offset signal based on the quadrature leakage level measurement.

Claims

1. An apparatus comprising:

an in-phase-quadrature (IQ) signal amplifier having an IQ baseband input;

an IQ mixer connected to the IQ signal amplifier, and the IQ mixer configured to be driven by an IQ carrier signal;

a carrier leakage detector connected to outputs of the IQ mixer, the carrier leakage detector configured to output an in-phase leakage level measurement and a quadrature leakage level measurement in the absence of an IQ baseband signal at the IQ baseband input;

a carrier-null offset signal generator connected to the carrier leakage detector configured to inject an in-phase carrier-null offset signal based on the in-phase leakage level measurement and to inject a quadrature carrier-null offset signal based on the quadrature leakage level measurement.

2. The apparatus of claim 1 wherein the carrier leakage detector is an RF to DC converter.

3. The apparatus of claim 1 wherein the carrier leakage detector is selected from the group consisting of a root-mean-squared detector, a log detector, and a diode detector.

4. The apparatus of claim 1 wherein the carrier-null offset signal generator comprises a digital-to-analog converter configured to generate a first voltage as the in-phase carrier-null offset signal and a second voltage as the quadrature carrier-null offset signal.

5. The apparatus of claim 1 wherein the carrier-null offset signal generator comprises a digital-to-analog converter configured to generate a first current as the in-phase carrier-null offset signal and a second current as the quadrature carrier-null offset signal.

6. The apparatus of claim 1 wherein the carrier-null offset signal generator comprises a successive approximation register.

7. The apparatus of claim 1 further comprising an IQ signal switch to selectively connect the carrier leakage detector to the outputs of the IQ mixer.

8. The apparatus of claim 1 further comprising an AC coupler configured to connect the carrier leakage detector to the outputs of the IQ mixer.

9. The apparatus of claim 1 further comprising a control circuit configured to connect the carrier leakage detector to the outputs of the IQ current commutating mixer, and configured to engage the carrier-null offset signal generator to inject the in-phase carrier-null offset signal and quadrature carrier-null offset signal.

10. The apparatus of claim 1, wherein the IQ mixer comprises an in-phase (I) mixer and a quadrature (Q) mixer, and the apparatus further comprises:

an in-phase switch to selectively connect the carrier leakage detector to the output of the in-phase (I) mixer; and

a quadrature switch to selectively connect the carrier leakage detector to the output the quadrature (Q) mixer.

11. The apparatus of claim 10, further comprising:

a first capacitor coupling the carrier leakage detector to the outputs of the in-phase (I) mixer via the in-phase switch; and

a second capacitor coupling the carrier leakage detector to the outputs of the quadrature (Q) mixer via the quadrature switch.

12. An apparatus comprising:

an in-phase signal amplifier having an in-phase baseband input and a quadrature signal amplifier having a quadrature baseband input;

an in-phase current commutating mixer and a quadrature current commutating mixer connected to the in-phase signal amplifier and the quadrature signal amplifier, respectively, and the in-phase current commutating mixer and the quadrature current commutating mixer configured to be driven by an in-phase carrier signal and a quadrature carrier signal, respectively;

a carrier leakage detector connected to an output of the in-phase current commutating mixer and connected to an output of the quadrature current commutating mixer, the carrier leakage detector configured to output an in-phase leakage level measurement based on a signal output of the in-phase current commutating mixer in the absence of an in-phase baseband signal at the in-phase baseband input and a quadrature leakage level measurement based on a signal output of the quadrature current commutating mixer in the absence of a quadrature baseband signal at the quadrature baseband input; and

a carrier-null offset signal generator connected to the carrier leakage detector configured to inject an in-phase carrier-null offset signal based on the in-phase leakage level measurement and to inject a quadrature carrier-null offset signal based on the quadrature leakage level measurement.

13. The apparatus of claim 12 wherein the carrier-null offset signal generator comprises a successive approximation register.

14. The apparatus of claim 12 further comprising an IQ signal switch to selectively connect the carrier leakage detector to the outputs of the in-phase and quadrature current commutating mixers.

15. The apparatus of claim 12 further comprising an AC coupler configured to connect the carrier leakage detector to the outputs of the in-phase and quadrature current commutating mixers.

16. The apparatus of claim 12 further comprising a control circuit configured to connect the carrier leakage detector to the outputs of the in-phase and quadrature current commutating mixers, and configured to engage the carrier-null offset signal generator to inject the in-phase carrier-null offset signal and quadrature carrier-null offset signal.

17. The apparatus of claim 12 wherein the carrier leakage detector is an RF to DC converter.

18. The apparatus of claim 12 wherein the carrier leakage detector is selected from the group consisting of a root-mean-squared detector, a log detector, and a diode detector.

19. The apparatus of claim 12, wherein the IQ mixer comprises an in-phase (I) mixer and a quadrature (Q) mixer, and the apparatus further comprises:

an in-phase switch to selectively connect the carrier leakage detector to the output of the in-phase (I) mixer; and

a quadrature switch to selectively connect the carrier leakage detector to the output the quadrature (Q) mixer.

20. The apparatus of claim 19, further comprising:

a first capacitor coupling the carrier leakage detector to the outputs of the in-phase (I) mixer via the in-phase switch; and

a second capacitor coupling the carrier leakage detector to the outputs of the quadrature (Q) mixer via the quadrature switch.

21. A method comprising:

setting a baseband input DC reference level where signal I(t), Q(t) are set to zero at an input to an IQ amplifier;

applying an IQ amplifier output, from the IQ amplifier, to a carrier signal mixer input;

obtaining a first measurement of a signal level of an output of the carrier signal mixer; and

injecting a carrier-null offset signal to the IQ amplifier based on the first measurement.

22. The method of claim 21, further comprising:

subsequent to injecting the carrier-null offset signal based on the first measurement, obtaining a second measurement of the carrier signal mixer output signal level; and

injecting the carrier-null offset signal based on the second measurement.

23. The method of claim 21, further comprising:

iteratively measuring a signal level of the output of the carrier signal mixer and adjusting the carrier-null offset signal.

24. The method of claim 21, further comprising:

selectively coupling the output of the carrier signal mixer to a carrier leakage detector.