Vector calibration system

• US 20060262872A1
• Filed: 07/24/2006
• Published: 11/23/2006
• Est. Priority Date: 03/15/2000
• Status: Abandoned Application

• Current Assignee: David C. Farden, Edwin A. Suominen, John W. Pierre, Richard C. Anderson-Sprecher, Roger A. Green
• Original Assignee: David C. Farden, Edwin A. Suominen, John W. Pierre, Richard C. Anderson-Sprecher, Roger A. Green
• Inventors: Suominen, Edwin A., Farden, David C., Pierre, John W., Anderson-Sprecher, Richard C., Green, Roger A.
• Application Number:
  US11/492,414
• Publication Number:
  US 20060262872A1
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels

Abstract

Among other things, calibration of a signal processing system is disclosed to minimize vector mismatch between signals frequency-translated from an RF signal and conveyed along a plurality of signal paths of the signal processing system. A calibration signal having a plurality of tones is coupled to the signal processing system such that it is frequency translated. The frequency-translated calibration signal is sampled along a first signal path of the signal processing system to obtain a first set of observed samples. It is also sampled along a second signal path of the system to obtain a second set of observed samples. The first set of observed samples is filtered with an adaptive filter having a set of adaptable coefficients to obtain a set of filtered samples. The coefficients are adapted to minimize undesired deviations between the set of filtered samples and the second set of observed samples.

Claims

1. A method for calibrating a signal processing system to minimize vector mismatch between signals frequency translated from an RF signal and conveyed along a plurality of signal paths of the signal processing system, the method comprising:

(a) applying a calibration signal having a plurality of tones to the signal processing system, such that the calibration signal is frequency translated;

(b) sampling the frequency-translated calibration signal (1) along a first signal path of the signal processing system to obtain a first set of observed samples and (2) along a second signal path of the signal processing system to obtain a second set of observed samples;

(c) filtering the first set of observed samples with an adaptive filter having adaptable coefficients to obtain a set of filtered samples; and

(d) adapting the coefficients to minimize undesired deviations between the set of filtered samples and the second set of observed samples.

2. The method of claim 1 further comprising using the filter with the adapted coefficients to minimize vector mismatch between signals frequency-translated by the signal processing system from an RF input signal of interest and conveyed along the first and second signal paths.

3. The method of claim 1 further comprising generating the calibration signal.

4. The method of claim 3 wherein generating the calibration signal comprises:

(a) generating a local oscillator signal, which signal the signal processing system uses to perform frequency translation;

(b) generating a baseband calibration signal; and

(c) mixing the local oscillator signal with the baseband calibration signal, thereby obtaining a radio frequency calibration signal.

5. The method of claim 1 wherein:

(a) the signal paths include an in-phase signal path and a quadrature signal path; and

(b) the filter coefficients are adapted to minimize deviations from a quadrature relationship between a signal on the in-phase signal path and a signal on the quadrature signal path.

6. The method of claim 1 wherein:

(a) the signal paths include a plurality of signal paths coupled to respective elements of a spatially selective array; and

(b) the filter coefficients are adapted to minimize deviations from a predetermined phase and amplitude relationship between signals on each respective one of the plurality of signal paths, such deviations degrading spatial selectivity of the array.

7. The method of claim 6 further comprising generating the calibration signal and transmitting it through an antenna placed at a fixed position with respect to the array elements.

8. The method of claim 1 wherein adapting is performed by a least mean squares algorithm.

9. The method of claim 8 wherein a plurality of values are determined by least mean squares constrained to a predetermined bounded region.

10. The method of claim 1 wherein:

(a) the signal paths include an in-phase signal path and a quadrature signal path; and

(b) the filter coefficients are adapted by a least mean squares algorithm to minimize deviations from a quadrature relationship between a signal on the in-phase signal path and a signal on the quadrature signal path.

11. The method of claim 10 further comprising:

(a) generating the calibration signal; and

(b) after adapting the filter coefficients, using the filter with the adapted coefficients to minimize deviations in a quadrature relationship between in-phase and quadrature signals frequency-translated by the signal processing system from an RF input signal of interest.

12. A signal processing system comprising:

(a) a frequency translation subsystem structured to produce a plurality of frequency-translated signals responsive to a calibration signal having a plurality of tones;

(b) one or more converters coupled to the frequency translation subsystem and structured to convert the signals into a plurality of sets of observed samples;

(c) an adaptive filter having adaptable coefficients and structured to produce a set of filtered samples responsive to one of the sets of observed samples; and

(d) control circuitry structured to adapt the filter coefficients to minimize undesired deviations between the set of filtered samples and a different one of the sets of observed samples.

13. The system of claim 12 further comprising a calibration signal subsystem coupled to the frequency translation subsystem and structured to produce the calibration signal.

14. The system of claim 12 wherein:

(a) the plurality of frequency-translated signals consists of an in-phase signal and a quadrature signal;

(b) the plurality of sets of observed samples consists of two sets of observed samples, one converted from the in-phase signal and the other converted from the quadrature signal; and

(c) the undesired deviations are deviations from a quadrature relationship between the in-phase signal and the quadrature signal.

15. The system of claim 12 wherein:

(a) the frequency-translated signals are from respective elements of a spatially selective array; and

(b) the undesired deviations are deviations from a predetermined phase and amplitude relationship between signals on each respective one of the plurality of signal paths, such deviations degrading spatial selectivity of the array.

16. The system of claim 12 further comprising:

(a) a front-end stage structured to produce a selectively amplified RF signal responsive to RF input;

(b) wherein the frequency translation subsystem is further coupled to the front-end stage and structured to produce frequency-translated in-phase and quadrature signals responsive to the selectively amplified RF signal from the front-end stage.

17. The system of claim 16 further comprising a switch coupled to the calibration signal subsystem and the front-end stage, and structured to convey a selected one of the calibration signal and the selectively amplified RF signal to the frequency translation subsystem for frequency translation into the in-phase and quadrature signals.

18. The system of claim 12 wherein the control circuitry is structured to adapt the filter coefficients by a least mean squares algorithm that determines a plurality of values by least mean squares constrained to a predetermined bounded region.

19. The system of claim 12 further comprising:

(a) a switch;

(b) a calibration signal subsystem selectably coupled to the frequency translation subsystem via the switch and structured to produce the calibration signal; and

(c) a front-end stage selectably coupled to the frequency translation subsystem via the switch and structured to produce a selectively amplified RF signal responsive to RF input;

(d) wherein the frequency translation subsystem is structured to produce frequency-translated in-phase and quadrature signals responsive to either one of (1) the calibration signal, and (2) the selectively amplified RF signal from the front-end stage.

20. The system of claim 19 wherein:

(a) the plurality of frequency-translated signals consists of an in-phase signal and a quadrature signal;

(b) the plurality of sets of observed samples consists of two sets of observed samples, one converted from the in-phase signal and the other converted from the quadrature signal; and

(c) the undesired deviations are deviations from a quadrature relationship between the in-phase signal and the quadrature signal.

21. The system of claim 20 wherein the control circuitry is structured to adapt the filter coefficients by a least mean squares algorithm that determines a plurality of values by least mean squares constrained to a predetermined bounded region.

22. A signal processing system comprising:

(a) means for generating a calibration signal having a plurality of tones;

(b) means for producing a plurality of frequency-translated signals responsive to the calibration signal;

(c) means for producing filtered samples from one of the frequency-translated signals, using a set of adaptable coefficients; and

(d) means for adapting the filter coefficients to minimize undesired deviations between the filtered samples and a different one of the frequency-translated signals.

23. The system of claim 22 further comprising means for receiving and frequency translating an RF input signal to the plurality of frequency-translated signals with undesired deviations between the signals minimized by the adaptation of the filter coefficients.

24. The system of claim 22 wherein the plurality of frequency-translated signals consists of an in-phase signal and a quadrature signal and the undesired deviations are deviations from a quadrature relationship between the two signals.

25. The system of claim 22 wherein the calibration signal is phase-synchronous with a local oscillator signal employed for producing a plurality of frequency-translated signals responsive to the calibration signal.