Adaptive linearization of power amplifiers

• US 6,246,286 B1
• Filed: 10/26/1999
• Issued: 06/12/2001
• Est. Priority Date: 10/26/1999
• Status: Expired due to Term

• Current Assignee: Fingerprint Cards AB
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Persson, Jonas
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Choe, Henry
• Application Number:
  US09/427,773
• Time in Patent Office: 595 Days
• Field of Search: 330/149, 330/136, 375/296, 375/297, 455/126, 455/127
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence

Abstract

A method and apparatus adaptively compensates for nonlinearities of a power amplifier by measuring a distortion characteristic across the power amplifier during amplification of a distortion detection signal. The distortion detection signal has a well-defined input power versus time relationship, such as ramp-up signal or ramp-down signal. Due to this well-defined relationship, the distortion characteristic can be calculated as a function of the input power level. This calculated function is then utilized to update a predistortion lookup table.

Claims

1. A method for adaptively compensating for a distortion characteristic of a power amplifier, the method comprising the steps of:

measuring the distortion characteristic across the power amplifier during amplification of a distortion detection signal, the distortion detection signal having a defined input power characteristic;

calculating a relationship between the measured distortion characteristic and input power;

updating a predistortion lookup table in accordance with the calculated relationship; and

wherein the step of measuring is performed using a pair of detectors, a first detector of the pair of detectors connected to an input terminal of the power amplifier, and a second detector of the pair of detectors connected to an output terminal of the power amplifier.

2. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the distortion characteristic comprises phase distortion.

3. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the distortion characteristic comprises envelope distortion.

4. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the distortion detection signal comprises at least one of an up-ramp signal and a down-ramp signal.

5. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the distortion detection signal comprises at least one of a burst up-ramp signal and a burst down-ramp signal.

6. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the method is performed only once per communication burst.

7. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the method is performed during only a portion of a communication burst.

8. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, further comprising the step of applying the updated predistortion lookup table to an input data stream.

9. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 8, wherein the step of updating and the step of applying are performed in a same communication burst.

10. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 8, wherein the step of measuring is performed in a first communication burst, and the step of applying is performed in a subsequent communication burst.

11. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the step of calculating the relationship is performed, at least in part, using a mean distortion characteristic measured from two or more communication bursts.

12. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, further comprising the step of attenuating an output signal at the output terminal of the power amplifier by approximately a nominal gain of the power amplifier.

13. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, where in the step of measuring is performed only for input power levels that will be used by an input signal.

14. The method for adaptively compensating for a distortion characteristic of a power amplifier as in claim 1, wherein the method is performed in at least one of a mobile station, a base station and a data terminal.

15. An apparatus for linearizing a power amplifier, the apparatus comprising:

at least one detector adapted to measure a distortion characteristic across a power amplifier during amplification of a distortion detection signal, the distortion detection signal having a known input power characteristic;

a processor coupled to the at least one detector, the processor adapted to calculate a relationship between the measured distortion characteristic and input power of the power amplifier;

a predistortion lookup table storing predistortion coefficients, the processor being adapted to update the predistortion coefficients in accordance with the calculated relationship to adaptively compensate for the measured distortion characteristic; and

wherein the at least one detector comprises a pair of detectors, a first detector of the pair of detectors connected to an output of the power amplifier, and a second detector of the pair of detectors connected to an input of the power amplifier.

16. The apparatus for linearizing a power amplifier as in claim 15, wherein the distortion characteristic comprises phase distortion.

17. The apparatus for linearizing a power amplifier as in claim 15, wherein the distortion characteristic comprises amplitude distortion.

18. The apparatus for linearizing a power amplifier as in claim 15, wherein the distortion characteristic comprises phase distortion and amplitude distortion.

19. The apparatus for linearizing a power amplifier as in claim 15, wherein the distortion detection signal comprises at least one of an up-ramp signal and a down-ramp signal.

20. The apparatus for linearizing a power amplifier as in claim 15, wherein the distortion detection signal comprises at least one of a burst up-ramp signal and a burst down-ramp signal.

21. The apparatus for linearizing a power amplifier as in claim 15, wherein the processor updates the predistortion coefficients only once per communication burst.

22. The apparatus for linearizing a power amplifier as in claim 15, wherein the processor calculates the relationship between the measured distortion characteristic and input power based, at least in part, on a mean distortion characteristic measured from two or more communication bursts.

23. The apparatus for linearizing a power amplifier as in claim 15, wherein the at least one detector measures the distortion characteristic during only a portion of a communication burst.

24. The apparatus for linearizing a power amplifier as in claim 15, further comprising a predistortion unit that predistorts an input data stream in accordance with the predistortion coefficients.

25. The apparatus for linearizing a power amplifier as in claim 24, wherein the processor updates the predistortion coefficients in a first communication burst and the predistortion unit predistorts the input data stream using the updated predistortion coefficients in the first communication burst.

26. The apparatus for linearizing a power amplifier as in claim 24, wherein the at least one detector measures the distortion characteristic in a first communication burst and the predistortion unit predistorts the input data stream using the updated predistortion coefficients in a subsequent communication burst.

33. The apparatus for linearizing a power amplifier as in claim 15, wherein the apparatus is used in at least one of a mobile station, a base station and a data terminal.

27. An apparatus for linearizing a power amplifier, the apparatus comprising:

at least one detector adapted to measure a distortion characteristic across a power amplifier during amplification of a distortion detection signal, the distortion detection signal having a known input power characteristic;

a processor coupled to the at least one detector, the processor adapted to calculate a relationship between the measured distortion characteristic and input power;

a predistortion lookup table storing predistortion coefficients, the processor being adapted to update the redistortion coefficients in accordance with the calculated relationship to adaptively compensate for the measured distortion characteristic; and

wherein the at least one detector comprises a pair of phase detectors, a first phase detector of the pair of phase detectors connected to an output of the power amplifier, and a second phase detector of the pair of detectors connected to an input of the power amplifier.

28. The apparatus for linearizing a power amplifier as in claim 27, wherein the output of the power amplifier is attenuated by approximately a nominal gain of the power amplifier before being applied to the first phase detector.

29. The apparatus for linearizing a power amplifier as in claim 27, further comprising a pair of mixers adapted to down-convert an input signal from an RF frequency to an intermediate frequency, a first mixer of the pair of mixers deposed between the output of the power amplifier and the first phase detector, and a second mixer of the pair of mixers deposed between the input of the power amplifier and the second phase detector.

30. An apparatus for linearizing a power amplifier, the apparatus comprising:

at least one detector adapted to measure a distortion characteristic across a power amplifier during amplification of a distortion detection signal, the distortion detection signal having a known input power characteristic;

a processor coupled to the at least one detector, the processor adapted to calculate a relationship between the measured distortion characteristic and input power;

a predistortion lookup table storing predistortion coefficients, the processor being adapted to update the predistortion coefficients in accordance with the calculated relationship to adaptively compensate for the measured distortion characteristic; and

wherein the at least one detector comprises a pair of envelope detectors, a first envelope detector of the pair of envelope detectors connected to an output of the power amplifier, and a second envelope detector of the pair of envelope detectors connected to an input of the power amplifier.

31. The apparatus for linearizing a power amplifier as in claim 30, wherein the output of the power amplifier is attenuated by approximately a nominal gain of the power amplifier before being applied to the first envelope detector.

32. The apparatus for linearizing a power amplifier as in claim 30, further comprising a pair of mixers adapted to down-convert an input signal from an RF frequency to an intermediate frequency, a first mixer of the pair of mixers deposed between the output of the power amplifier and the first envelope detector, and a second mixer of the pair of mixers deposed between the input of the power amplifier and the second envelope detector.