Feed forward distortion reduction system

• US 6,583,739 B1
• Filed: 01/24/2002
• Issued: 06/24/2003
• Est. Priority Date: 07/28/1999
• Status: Expired due to Fees

• Current Assignee: Andrew LLC (CommScope Holding Company, Inc.)
• Original Assignee: Andrew Corporation (CommScope Holding Company, Inc.)
• Inventors: Kenington, Peter
• Primary Examiner(s): Jeanglaude, Jean Bruner
• Application Number:
  US10/048,300
• Time in Patent Office: 516 Days
• Field of Search: 341/118, 341/119, 341/117, 341/120, 330/149, 330/136, 330/151
• US Class Current: 341/118
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3294 Acting on the real and imaginary components of the input signal

Abstract

The lineariser (1) comprises a digital signal processor (DSP) (100) for reducing distortion of the output of non-linear RF power amplifier (200). The DSP (100) implements a predistorter process (102) which predistorts the input to amplifier (200) in such a manner as to counter distortion imposed by the amplifier. Feedback from the amplifier output is sampled at (212) to provide a feedback signal for controlling the predistortion process. Additionally, a feedforward signal is combined with the amplifier output at (216) to further reduce distortion therein. The feedforward signal is derived by subtracting the input signal, at (112), from feedback from the output of amplifier (200) (which may contain residual distortion). The vector modulator (114) conditions the result of the subtraction process (112) to produce the feedforward signal. To ensure maximum cancellation of distortion in the output of amplifier (200), the vector modulator is adapted using feedback from the output of amplifier (200) (removed at 218) which is correlated with a reference signal produced by distorter (102). The reference signal contains components which correspond to some or all of the intermodulations distortion components which can be generated by amplifier (200).

Claims

1. An arrangement for reducing distortion of an output signal provided by signal handling equipment in response to an input signal, the arrangement comprising a feed forward corrector which derives a feed forward signal from the input signal and combines it with the output signal to reduce distortion thereof, and a predistorter which predistorts the input signal prior to the signal handling equipment to counter distortion caused thereby, wherein the predistorter also derives a reference signal from the input signal for use in controlling the feed forward signal.

2. An arrangement according to claim 1, wherein the reference signal comprises components which correspond to intermodulation distortion components which could be introduced by the signal handling equipment.

3. An arrangement according to claim 1, wherein the reference signal is created in the digital domain.

4. An arrangement according to claim 1, further comprising a first controller for adapting feed forward signal using a first feedback signal derived from the output signal.

5. An arrangement according to claim 4, wherein the first feedback signal is derived from the output signal after its combination with the feed forward signal.

6. An arrangement according to claim 4, wherein the first controller correlates the reference signal with the first feedback signal.

7. An arrangement according to claim 6, wherein the correlation process comprises mixing the reference signal with the first feedback signal and integrating the result to produce a control signal for the feed forward corrector.

8. An arrangement according to claim 1, further comprising a second controller for adapting the predistortion applied by the predistorter using a second feedback signal derived from the output signal.

9. An arrangement according to claim 1, wherein the predistorter predistorts the input signal by using a polynominal distortion generation process to produce a distortion signal for combination with the input signal.

10. An arrangement according to claim 1, wherein the predistorter predistorts the input signal by using coefficients from a lookup table to process the input signal to produce a predistorted input signal.

11. An arrangement according to claim 1, wherein the signal handling equipment comprises an amplifier.

12. An arrangement according to claim 1, wherein:

a predistorted input signal from the predistorter is upconverted to an intermediate frequency (IF) based on a first oscillator frequency prior to being applied to the signal handling equipment;

the reference signal from the predistorter is upconverted based on a second oscillator frequency offset from the first oscillator frequency by an audio frequency (AF) offset;

the upconverted reference signal is mixed with a feed back signal derived from the output signal generated by the signal handling equipment to generate a mixed feed back signal; and

the mixed feed back signal is used to control generation of the feed forward signal.

13. An arrangement according to claim 12, wherein:

the mixed feed back signal is downconverted based on the AF offset frequency; and

the downconverted mixed feed back signal is integrated to generate a control signal used to control operations of a vector modulator used in generating the feed forward signal.

14. An arrangement according to claim 1, wherein the predistorter generates at least two signals:

the reference signal and a predistorted input signal that is applied to the signal handling equipment.

15. A method for reducing distortion of an output signal provided by signal handling equipment in response to an input signal, the method comprising a feed forward step of deriving a feed forward signal from the input signal and combining it with the output signal to reduce distortion thereof, a predistorting step comprising predistorting, using a predistorter, the input signal prior to the signal handling equipment to counter distortion caused by the signal handling equipment, and a generating step of generating a reference signal from the input signal using the predistorter for use in controlling the feed forward signal.

16. A method according to claim 15, wherein the reference signal comprises components which correspond to intermodulation distortion components which could be generated by the signal handling equipment.

17. A method according to claim 15, wherein the reference signal is created in the digital domain.

18. A method according to claim 15, further comprising a first control step of adapting the feed forward signal using a first feed back signal derived from the output signal.

19. A method according to claim 18, wherein the first feed back signal is derived from the output signal after its combination with the feed forward signal.

20. A method according to claim 18, wherein the first control step comprises correlating the reference signal with the first feed back signal.

21. A method according to claim 20, wherein the correlation process comprises mixing or multiplying the reference signal with the first feed back signal and integrating the result to produce a control signal.

22. A method according to claim 15, wherein the feed forward signal is produced by performing a subtraction on the input signal and a second feed back signal derived from the output signal.

23. A method according to claim 22, wherein the second feed back signal is derived from the output signal prior to its combination with the feed forward signal.

24. A method according to claim 22, wherein the subtraction uses the input signal prior to its predistortion.

25. A method according to claim 22, wherein the predistorting step comprises generating a distortion signal by distorting the input signal using a polynominal distortion generation process and combining the distortion signal with the input signal.

26. A method according to claim 22, wherein the predistorting step comprises generating a distortion signal by distorting the input signal using coefficients retrieved from a lookup table to produce the predistorted input signal.

27. A method according to claim 22, wherein the signal handling equipment is an amplifier.

28. A method according to claim 15, wherein:

a predistorted input signal from the predistorter is upconverted to an intermediate frequency (IF) based on a first oscillator frequency prior to being applied to the signal handling equipment;

the reference signal from the predistorter is upconverted based on a second oscillator frequency offset from the first oscillator frequency by an audio frequency (AF) offset;

the upconverted reference signal is mixed with a feed back signal derived from the output signal generated by the signal handling equipment to generate a mixed feed back signal; and

the mixed feed back signal is used to control generation of the feed forward signal.

29. A method according to claim 28, wherein:

the mixed feed back signal is downconverted based on the AF offset frequency; and

the downconverted mixed feed back signal is integrated to generate a control signal used to control operations of a vector modulator used in generating the feed forward signal.

30. A method according to claim 15, wherein the predistorter generates at least two signals:

the reference signal and a predistorted input signal that is applied to the signal handling equipment.