Amplitude imbalance compensation of quadrature modulator

• US 6,700,453 B2
• Filed: 06/18/2002
• Issued: 03/02/2004
• Est. Priority Date: 06/18/2002
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Heiskala, Juha, Kuru, Lauri
• Primary Examiner(s): Wells, Kenneth B.
• Application Number:
  US10/173,574
• Publication Number:
  US 20030231075A1
• Time in Patent Office: 623 Days
• Field of Search: 332/103-105, 332/149-153
• US Class Current: 332/103
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0018 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

A method and an arrangement for compensating for amplitude imbalance of a quadrature modulator including: determining a first correlation on the basis of a first modulation signal and an output signal of the quadrature modulator; determining a second correlation on the basis of a second modulation signal and the output signal of the quadrature modulator; producing a compensation signal proportional to the amplitude imbalance on the basis of a ratio of the determined correlations and the first and second modulation signals; and processing at least one of the modulation signals of the quadrature modulator with the compensation signal; wherein determining the correlations uses unprocessed modulation signals of the quadrature modulator for determining the correlations.

Claims

1. A method for compensating for amplitude imbalance of a quadrature modulator comprising:

determining a first correlation on the basis of a first modulation signal and an output signal of the quadrature modulator;

determining a second correlation on the basis of a second modulation signal and the output signal of the quadrature modulator;

producing a compensation signal proportional to the amplitude imbalance on the basis of a ratio of the determined correlations and the first and second modulation signals; and

processing at least onewof the modulation signals of the quadrature modulator with the compensation signal;

wherein the correlations are determined on the basis of unprocessed modulation signals of the quadrature modulator.

2. The method of claim 1, wherein the output signal of the quadrature modulator used for determining the correlations is an amplified output signal.

3. The method of claim 1, wherein the first correlation is a correlation between power of the output signal and square of the first modulation signal and the second correlation is a correlation between power of the output signal and square of the second modulation signal.

4. The method of claim 1, wherein the production of the compensation signal comprises:

producing an error signal proportional to the amplitude imbalance on the basis of a ratio of the determined correlations and the first and second modulation signals; and

producing the compensation signal on the basis of the error signal.

5. The method of claim 4, wherein the error signal is set to be equal to zero when there is no amplitude imbalance.

6. The method of claim 4 or 5, wherein the compensation signal is produced by integrating the error signal over time.

7. The method of claim 6, wherein the error signal is low pass filtered prior to integration.

8. The method of claim 7, wherein the error signal is filtered with a filter having a gain factor less than unity.

9. The method of claim 8, wherein the gain factor of the filter is adjusted according to the amount of amplitude imbalance.

10. The method of claim 1, wherein the processing of at least one of the modulation signals with the compensation signal is performed by dividing or multiplying at least one of the modulation signals with the compensation signal.

11. The method of claim 1, wherein the processing at least one of the modulation signals with the compensation signal is performed by dividing or multiplying at least one of the modulation signals with an approximation of the compensation signal.

12. An arrangement for compensating for an amplitude imbalance of a quadrature modulator comprising:

means for determining a first correlation on the basis of a first modulation signal and an output signal of the quadrature modulator;

means for determining a second correlation on the basis of a second modulation signal and the output signal of the quadrature modulator;

means for producing a compensation signal proportional to the amplitude imbalance on the basis of a ratio of the determined correlations and the first and second modulation signals; and

means for processing at least one of the modulation signals of the quadrature modulator with the compensation signal;

wherein the means for determining the correlations are arranged to use unprocessed modulation signals of the quadrature modulator for determining the correlations.

13. The arrangement of claim 12, wherein the output signal of the quadrature modulator is an amplified output signal.

14. The arrangement of claim 12, wherein the first correlation is a correlation between power of the output signal and square of the first modulation signal and the second correlation is a correlation between power of the output signal and square of the second modulation signal.

15. The arrangement of claim 12, wherein the means for producing the compensation signal comprise:

means for producing an error signal proportional to the amplitude imbalance on the basis of a ratio of the determined correlations and the first and second modulation signals; and

means for producing the compensation signal on the basis of the error signal.

16. The arrangement of claim 15, wherein the means for producing the error signal are arranged to set the error signal to be equal to zero when there is no amplitude imbalance.

17. The arrangement of claim 15 or 16, wherein the means for producing the compensation signal on the basis of the error signal are arranged to produce the compensation signal by integrating the error signal over time.

18. The arrangement of claim 17, wherein the arrangement comprises means for filtering the error signal connected between the means for producing the error signal and the means for producing the compensation signal on the basis of the error signal.

19. The arrangement of claim 18, wherein the means for filtering the error signal has a gain factor less than unity.

20. The arrangement of claim 19, wherein the arrangement is arranged to adjust the gain factor of the means for filtering the error signal according to the amount of amplitude imbalance.

21. The arrangement of claim 12, wherein the means for processing at least one of the modulation signals are arranged to divide or multiply at least one of the modulation signals with the compensation signal.

22. The arrangement of claim 12, wherein the means for processing at least one of the modulation signals are arranged to divide or multiply at least one of the modulation signals with an approximation of the compensation signal.

23. An arrangement for compensating for amplitude imbalance of a quadrature modulator comprising:

a first correlator configured to determine a first correlation on the basis of a first modulation signal and an output signal of the quadrature modulator;

a second correlator configured to determine a second correlation on the basis of a second modulation signal and the output signal of the quadrature modulator;

means configured to produce a compensation signal proportional to the amplitude imbalance on the basis of a ratio of the determined correlations and the first and second modulation signals; and

means configured to process at least one of the modulation signals of the quadrature modulator with the compensation signal;

wherein the first and second correlators are configured to use unprocessed modulation signals of the quadrature modulator for determining the correlations.