APPARATUS AND METHOD FOR ADAPTIVE I/Q IMBALANCE COMPENSATION

• US 20120177151A1
• Filed: 01/06/2011
• Published: 07/12/2012
• Est. Priority Date: 01/06/2011
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Hormis, Raju
• Granted Patent: US 8,363,712 B2
• Time in Patent Office: Days
• US Class Current: 375/340
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal

Abstract

An I/Q imbalance compensation block of a RF receiver for compensating an imbalance between an in-phase component and a quadrature component of an RF signal is disclosed. The compensation block includes a conjugation block; an adaptive finite impulse response (FIR) filter; and an adder. The filter use filter coefficients iteratively updated at least partly in response to a compensated digital signal. The filter can have a complex number for at least one, but not all of filter taps, and real numbers for other filter taps. The filter can be provided with adaptation step sizes different from filter tap to filter tap. The filter can also be provided with an adaptation step size(s) varying over time. The filter can also be provided with an adaptation step size(s) divided by the square norm of the compensated signal.

Claims

1. An apparatus comprising:

a finite impulse response (FIR) filter configured to filter a version of a digital signal to generate a compensation signal, wherein the FIR filter has X real number filter coefficients and Y imaginary number coefficients, wherein Y is less than X, wherein the digital signal comprises a digital representation of a demodulated in-phase and quadrature phase component of a radio frequency (RF) signal; and

an adder configured to sum another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal;

wherein one of the versions of the digital signal or the version of the compensation signal is a complex conjugate of the digital signal or a complex conjugate of the compensation signal, respectively, and the others are not the complex conjugates, wherein the FIR filter and the adder comprise electronic hardware.

2. The apparatus of claim 1, wherein the FIR filter has only 1 imaginary number coefficient and the 1 imaginary number coefficient is present only for the first tap of the FIR filter.

3. The apparatus of claim 1, further comprising analog low-pass filters for anti-aliasing of analog-to-digital converters that generate components of the digital signal, wherein the analog low-pass filters have all-pole configurations.

4. The apparatus of claim 1, further comprising a complex conjugation circuit configured to perform a complex conjugation operation on the digital signal or the compensation signal to generate one of the versions of the digital signal or the version of the compensation signal, respectively.

5. The apparatus of claim 4, wherein the complex conjugation circuit generates a complex conjugate of the digital signal, and provides the complex conjugate of the digital signal to the FIR filter.

6. The apparatus of claim 5, further comprising:

a delay element configured to delay the balanced digital signal; and

a filter adaptation block configured to generate a feedback signal from the delayed balanced digital signal, and to provide the feedback signal to the FIR filter for updating the real and imaginary number filter coefficients.

7. The apparatus of claim 5, further comprising a feed forward block configured to generate a feed forward signal from the digital signal, and to provide the feed forward signal to the FIR filter for updating the real and imaginary number filter coefficients.

8. The apparatus of claim 4, wherein the FIR filter is configured to provide the complex conjugation circuit with the compensation signal by filtering the digital signal, and wherein the complex conjugation circuit is configured to provide the adder with a complex conjugate of the compensation signal.

9. The apparatus of claim 8, further comprising:

a delay element configured to delay the balanced digital signal;

a filter adaptation block configured to generate a feedback signal using the delayed balanced digital signal; and

a second complex conjugation circuit to provide a complex conjugate of the feedback signal to the FIR filter for updating the real and imaginary number filter coefficients.

10. The apparatus of claim 4, wherein the FIR filter is configured to provide the adder with the compensation signal by filtering the digital signal, and wherein the complex conjugation circuit provides the adder with a complex conjugate of the digital signal.

11. The apparatus of claim 10, further comprising:

a delay element configured to delay the balanced digital signal;

a filter adaptation block configured to generate a feedback signal using the delayed balanced digital signal, and to provide the feedback signal to the FIR filter for updating the real and imaginary number filter coefficients.

12. The apparatus of claim 1, further comprising an adaptation step size adaptor for providing two or more different adaptation step sizes for updating the filter coefficients.

13. The apparatus of claim 1, further comprising an adaptation step size adaptor for varying adaptation step sizes for one or more of the filter coefficients over time in updating the filter coefficients.

14. The apparatus of claim 1, further comprising an adaptation step size adaptor for dividing adaptation step sizes for one or more of the filter coefficients by the square norm of the balanced digital signal in updating the filter coefficients.

15. A method of improving an image rejection ratio of a digital signal having demodulated in-phase and quadrature-phase components of a radio frequency signal, the method comprising:

filtering a version of the digital signal with a finite impulse response (FIR) filter to generate a compensation signal, wherein the FIR filter has X real number filter coefficients and Y imaginary number coefficients, wherein Y is less than X, wherein filtering is implemented by hardware or by instructions implemented by a processor;

generating a complex conjugate of the digital signal or the compensation signal; and

summing another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal, wherein one of the versions of the digital signal and the version of the compensation signal corresponds to a complex conjugate of the digital signal or the compensation signal, respectively, and the others are not the complex conjugates.

16. The method of claim 15, wherein the FIR filter has only 1 imaginary number coefficient, wherein the imaginary number coefficient is present only for the first tap of the FIR filter.

17. The method of claim 15, further comprising performing anti-aliasing filtering of the demodulated in-phase component and the demodulated quadrature-phase component by filtering with analog low-pass filters that have all-pole configurations prior to analog-to-digital conversions used to generate the digital signal.

18. The method of claim 15, further comprising generating one of the versions of the digital signal by performing a complex conjugation of the digital signal.

19. The method of claim 15, further comprising:

delaying the balanced digital signal;

generating a feedback signal by multiplying the delayed balanced digital signal with an adaptation step size; and

determining the X real number coefficients and Y or fewer imaginary number coefficients, using the feedback signal.

20. An apparatus comprising:

an (N+1)-th order finite impulse response (FIR) filter configured to filter a version of a digital signal to generate a compensation signal, wherein the FIR filter has N taps, N real number filter coefficients, and N−

1 or fewer imaginary number coefficients, wherein the digital signal comprises a digital representation of a demodulated in-phase and quadrature phase component of a radio frequency (RF) signal;

means for generating a complex conjugate of the digital signal or the compensation signal; and

means for summing another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal, wherein one of the versions of the digital signal and the version of the compensation signal corresponds to a complex conjugate of the digital signal or the compensation signal, respectively, and the others are not the complex conjugates.

21. The apparatus of claim 20, wherein the FIR filter has only 1 imaginary number coefficient, wherein the imaginary number coefficient is present only for the first tap of the FIR filter.

22. The apparatus of claim 20, further comprising means for generating one of the versions of the digital signal by performing a complex conjugation of the digital signal.

23. The apparatus of claim 20, further comprising:

means for delaying the balanced digital signal; and

means for generating a feedback signal by multiplying the delayed balanced digital signal with an adaptation step size; and

wherein the FIR filter is configured to determine the filter coefficients, using the feedback signal.

24. An apparatus comprising:

a finite impulse response (FIR) filter configured to filter a version of a digital signal to generate a compensation signal, wherein the FIR filter has X real number filter coefficients and X imaginary number coefficients, wherein at least one, but not all, of the imaginary number coefficients is 0, wherein the digital signal comprises a digital representation of a demodulated in-phase and quadrature phase component of a radio frequency (RF) signal; and

an adder configured to sum another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal;

wherein one of the versions of the digital signal or the version of the compensation signal is a complex conjugate of the digital signal or a complex conjugate of the compensation signal, respectively, and the others are not the complex conjugates, wherein the FIR filter and the adder comprise electronic hardware.