Resource Efficient Adaptive Digital Pre-Distortion System

• US 20100225390A1
• Filed: 11/11/2009
• Published: 09/09/2010
• Est. Priority Date: 11/11/2008
• Status: Active Grant

• Current Assignee: Aceaxis Limited
• Original Assignee: Aceaxis Limited
• Inventors: Friedman, Frank, Brown, Philip, Segar, Jeremy, Cooper, Stephen, Ibison, John
• Granted Patent: US 8,030,997 B2
• Time in Patent Office: Days
• US Class Current: 330/149
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence

Abstract

A digital pre-distortion system which can provide the flexibility to model the highly non-linear distortion associated with High Efficiency RF Power Amplifiers while through a novel implementation of a least squares estimation process allows an implementation well suited for an FPGA application where limited resources and in particular memory resources are available.

Claims

1-9. -9. (canceled)

10. A method comprising:

distortion adjusting a signal for input to a radio frequency amplifier by processing the signal through a pre-distortion facility that contains a plurality of lookup tables of coefficients that are calculated from a subset of coefficients obtained by sampling a non-linearity characteristic of the amplifier.

11. The method of claim 10, wherein a preferred subset of coefficients is determined based on the signal magnitude input to the amplifier.

12. The method of claim 10, wherein the coefficients in each of the plurality of lookup tables are interdependently calculated.

13. The method of claim 10, wherein the pre-distortion facility comprises a non-linear complex FIR filter whose coefficients are contained in the plurality of lookup tables.

14. The method of claim 10, wherein the distortion adjusting includes applying each of a plurality of time-delayed samples of the signal to a corresponding one of the plurality of lookup tables to produce a plurality of time-delayed results and summing the plurality of time-delayed results.

15. The method of claim 10, wherein at least some coefficients are determined using a least squares optimized model of time varying non-linearity characteristics of the amplifier.

16. The method of claim 15, wherein a second one of the time-delayed samples is delayed from a first one of the time-delayed samples by at least two sample times.

17. The method of claim 10, wherein at least some coefficients are derived from amplifier distortion values captured at different amplifier power levels.

18. The method of claim 10, wherein the coefficients are piecewise linearly interpolated from the subset of coefficients.

19-31. -31. (canceled)

32. A method comprising:

digitally estimating a radio frequency amplifier non-linearity using a plurality of magnitude differentiated amplifier samples to form a complex matrix equation that produces a subset of filter coefficients suitable for interpolation to provide a model of the inverse of the amplifier non-linearity.

33. The method of claim 32, wherein the amplifier samples include input signal and output signal samples.

34. The method of claim 32, wherein at least some coefficients are based on a least squares optimized model of time varying amplifier non-linearity characteristics.

35. The method of claim 32, wherein at least some coefficients are derived from amplifier distortion values captured at different amplifier power levels.

36. The method of claim 32, wherein the model includes coefficients that are piecewise linearly interpolated from the subset of coefficients.

37. The method of claim 32, wherein the model includes coefficients that are matched to levels of corresponding bins of sample coefficients.

40. The method of claim 32, wherein the matrix of the model is configured as a square matrix to facilitate convenient processing of mathematical operations.

38-39. -39. (canceled)

41-113. -113. (canceled)

114. A method comprising:

using a processor to generate a distortion adjustment model merit of accuracy by determining a difference between a signal input to the model and a signal output from the model, wherein the distortion adjustment model is used by a pre-distortion facility for distortion adjusting a radio frequency signal; and

optimizing a portion of the model based on the merit of accuracy.

115. The method of claim 114, wherein optimizing includes updating a portion of at least one lookup table.

116. The method of claim 114, further including using the processor to calculate a merit of accuracy of a candidate distortion adjustment model and updating the distortion adjustment model based on a comparison of the merit of accuracy of the candidate distortion adjustment model with the merit of accuracy of the distortion adjustment model.

117. The method of claim 116, wherein updating occurs if the comparison indicates improved pre-distortion facility accuracy if the update occurs.