Method and apparatus for adaptive digital predistortion using nonlinear and feedback gain parameters

• US 20050231279A1
• Filed: 04/15/2004
• Published: 10/20/2005
• Est. Priority Date: 04/15/2004
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Saunders, Jeffrey H., Moffatt, James P.
• Granted Patent: US 7,113,036 B2
• Time in Patent Office: Days
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3252 using multiple parallel paths between input and output H03F1/3258, H03F1/3282, H03F1/3294 take precedence
• CPC Class Codes: H03F 1/3258 based on polynomial terms
• CPC Class Codes: H03F 1/3294 Acting on the real and imaginary components of the input signal

Abstract

A predistorter is disclosed that predistorts an input signal based on one or more static coefficients that are representative of a non-linear distortion characteristic of an amplifier. The input signal is also processed based on a non-linear gain parameter that reduces an error metric between the input signal and a feedback signal. The nonlinear gain parameter adapts an amount of nonlinearity introduced by the predistorter. The non-linear gain adaptation is performed, for example, when the input voltage is above a threshold input voltage. The input signal can be processed by multiplying the input signal by the non-linear gain parameter followed by table-coefficient processing, or by both multiplying the input by the non-linear gain parameter followed by dividing the table-coefficient processed output signal by the same non-linear gain parameter. The input signal can also be processed based on a feedback gain parameter that compensates for a small-signal gain of the feedback loop. The feedback gain parameter attempts to maintain a small-signal gain of approximately unity.

Claims

1. A method for predistorting an input signal, comprising:

predistorting said input signal based on one or more static coefficients representative of a non-linear distortion characteristic of an amplifier; and

processing said input signal based on a non-linear gain parameter that reduces an error metric between said input signal and a feedback signal following said amplifier.

2. The method of claim 1, wherein said non-linear gain parameter is adapted when said input voltage is above a threshold input voltage.

3. The method of claim 2, wherein said threshold input voltage identifies a compression zone.

4. The method of claim 1, wherein said nonlinear gain parameter adapts an amount of nonlinearity introduced by said predistorting step.

5. The method of claim 1, wherein said error metric comprises a squared difference between said input signal and said feedback signal following said amplifier.

6. The method of claim 1, further comprising the step of processing said input signal based on a feedback gain parameter.

7. The method of claim 6, wherein said feedback gain parameter compensates for a small-signal gain of a feedback loop that generates said feedback signal.

8. The method of claim 6, wherein said small-signal gain is approximately unity.

9. The method of claim 6, wherein said small-signal gain is a difference between said input signal and said feedback signal.

10. The method of claim 1, further comprising the step of applying said predistorted signal to said amplifier.

11. The method of claim 1, wherein said step of processing said input signal further comprises the step of multiplying said input signal by said non-linear gain parameter.

12. The method of claim 11, wherein said step of processing said input signal further comprises the step of dividing said input signal by said non-linear gain parameter.

13. The method of claim 1, wherein said non-linear distortion characteristic comprises an AM/AM characteristic.

14. The method of claim 1, wherein said non-linear distortion characteristic comprises an AM/PM characteristic.

15. The method of claim 1, further comprising the step of digitizing said input signal prior to said predistorting step.

16. A predistorter that processes an input signal, comprising:

means for predistorting said input signal based on one or more static coefficients representative of a non-linear distortion characteristic of an amplifier; and

means for processing said input signal based on a non-linear gain parameter that reduces an error metric between said input signal and a feedback signal following said amplifier.

17. The predistorter of claim 16, wherein said means for processing step is only performed when said input voltage is above a threshold input voltage.

18. The predistorter of claim 16, wherein said nonlinear gain parameter adapts an amount of nonlinearity introduced by said predistorter.

19. The predistorter of claim 16, wherein said error metric is a squared difference between said input signal and said feedback signal following said amplifier.

20. The predistorter of claim 16, further comprising the step of processing said input signal based on a feedback gain parameter that compensates for a small-signal gain of a feedback loop that generates said feedback signal.

21. The predistorter of claim 16, further comprising a multiplier for multiplying said input signal by said non-linear gain parameter.

22. The predistorter of claim 21, further comprising a divider for dividing said input signal by said non-linear gain parameter.

23. The predistorter of claim 16, wherein said static coefficients are implemented using a look-up table.

24. The predistorter of claim 16, wherein said static coefficients are implemented using one or more multipliers.

25. An integrated circuit, comprising:

a predistorter that processes an input signal based on one or more static coefficients representative of a non-linear distortion characteristic of an amplifier and a non-linear gain parameter that reduces an error metric between said input signal and a feedback signal following said amplifier; and

an adaptive circuit that adjusts said non-linear gain parameter based on said error metric.