Wideband digital predistortion linearizer for nonlinear amplifiers

• US 6,798,843 B1
• Filed: 06/16/2000
• Issued: 09/28/2004
• Est. Priority Date: 07/13/1999
• Status: Expired due to Term

• Current Assignee: Maxlinear Asia Singapore Pte Ltd. (Maxlinear Incorporated)
• Original Assignee: PMC-Sierra Incorporated (Microchip Technology Incorporated)
• Inventors: Bennett, Steven J., Wright, Andrew S., Klijsen, Bartholomeus T. W., Yee, Paul V., Hung, Chun Yeung Kevin
• Primary Examiner(s): Bocure, Tesfaldet
• Assistant Examiner(s): GHULAMALI, QUTBUDDIN
• Application Number:
  US09/596,142
• Time in Patent Office: 1,565 Days
• Field of Search: 375/296, 375/297, 330/10, 330/107, 330/149, 332/160-162, 455/126
• US Class Current: 375/296
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• 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
• CPC Class Codes: H03F 2201/3209 the amplifier comprising means for compensating memory effects
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion

Abstract

A wideband predistortion system compensates for a nonlinear amplifier'"'"'s frequency and time dependent distortion characteristics. The system comprises a data structure in which each element stores a set of compensation parameters (preferably including FIR filter coefficients) for predistorting the wideband input transmission signal. The parameter sets are preferably indexed within the data structure according to multiple signal characteristics, such as instantaneous amplitude and integrated signal envelope, each of which corresponds to a respective dimension of the data structure. To predistort the input transmission signal, an addressing circuit digitally generates a set of data structure indices from the input transmission signal, and the indexed set of compensation parameters is loaded into a compensation circuit which digitally predistorts the input transmission signal. The sets of compensation parameters are generated periodically and written to the data structure by an adaptive processing component that performs a non-real-time analysis of amplifier input and output signals.

Claims

1. A system for digitally predistorting a wideband input signal to a power amplifier, comprising:

a multi-dimensional data structure in which each element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal to compensate for nonlinearities in an amplification process;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the input signal, to read sets of compensation parameters from the data structure, wherein the addressing circuit generates a first index that represents an instantaneous characteristic of the wideband input signal, and generates a second index that represents an averaged characteristic of the wideband input signal, and uses the first and second indexes in combination to address the multi-dimensional data structure such that the first and second indexes correspond respectively to first and second dimensions of the multi-dimensional data structure; and

a digital compensation circuit that predistorts the input signal in real time using the compensation parameters read from the multi-dimensional data structure according to the addressing circuit, wherein the digital compensation circuit comprises a finite impulse response (FIR) filter for which coefficient sets are read from the multi-dimensional data structure;

whereby a predistortion function applied by the digital compensation circuit is dependent upon the characteristics of the wideband input signal.

2. The system as in claim 1, wherein the first characteristic is an instantaneous amplitude or power of the input signal, and the second characteristic is an integrated signal envelope of the input signal.

3. The system as in claim 1, wherein the addressing circuit further generates a third index that represents a third characteristic of the digital input signal and corresponds to a third dimension of the multi-dimensional data structure.

4. The system as in claim 3, wherein the third characteristic is a rate of change of the input signal.

5. The system as in claim 1, wherein the addressing circuit comprises an integration filter that generates an integrated signal envelope of the input signal.

6. The system as in claim 1, wherein the addressing circuit comprises a temperature sensor that measures a transistor die temperature of the power amplifier.

7. The system as in claim 1, wherein the coefficient sets are read from the multi-dimensional data structure and loaded into the FIR filter on a sample-by-sample basis.

8. The system as in claim 1, wherein the FIR filter has non-uniform delay steps between each tap.

9. The system as in claim 1, wherein the FIR filter has uniform delay steps between each tap, wherein the delay steps exceed the sampling period used by the system.

10. The system as in claim 1, wherein the digital compensation circuit further comprises an IQ modulator correction circuit.

11. The system as in claim 1, wherein the digital compensation circuit comprises a first digital filter that processes the input signal and comprises a second digital filter that independently processes a second order multiple of the input signal, wherein outputs of at least the first and second digital filters are summed to form a compensated input signal.

12. The system as in claim 11, wherein the multi-dimensional data structure stores sets of coefficients for the first and second digital filters.

13. The system as in claim 1, wherein the digital compensation circuit comprises:

means for generating higher order multiples of the input signal;

means for independently filtering the input signal and each higher order multiple of the input signal; and

means for combining the input signal and the higher order multiples of the input signal after filtering to form a compensated input signal.

14. The system as in claim 1, wherein the digital compensation circuit corrects for at least amplitude dependent and frequency dependent variations in the gain and phase rotation introduced by the power amplifier.

15. The system as in claim 1, wherein the compensation parameters stored within the multi-dimensional data structure include IQ modulator correction coefficients.

16. The system as in claim 1, further comprising an automatic gain control circuit that dynamically adjusts an output of the digital compensation circuit prior to amplification.

17. The system as in claim 1, wherein the wideband input signal has an envelope that varies in amplitude and phase.

18. The system as in claim 1, wherein the addressing circuit comprises a two-dimensional ROM circuit indexed by real and imaginary signal components.

19. A linear wideband amplifier system, comprising:

a nonlinear amplification chain along which a wideband input signal is upconverted and amplified for transmission;

a multi-dimensional data structure in which each storage element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the wideband input signal, to read sets of compensation parameters from the data structure for use, wherein the addressing circuit generates a first index that represents an instantaneous characteristic of the wideband input signal, and generates a second index that represents an averaged characteristic of the wideband input signal, and uses the first and second indexes in combination to address the multi-dimensional data structure such that the first and second indexes correspond respectively to first and second dimensions of the multi-dimensional data structure;

a digital compensation circuit that predistorts the wideband input signal, prior to processing along the amplification chain, using the sets of compensation parameters read from the multi-dimensional data structure, to compensate for nonlinearities in the amplification chain;

an adaptive compensation estimator that generates the sets of compensation parameters stored in the multi-dimensional data structure based on a non-real-time analysis of signals within the amplifier system; and

a feedback circuit that generates a digital observation signal which represents an output of the amplification chain, and provides the digital observation signal to the adaptive compensation estimator.

20. The linear wideband amplifier system as in claim 19, wherein the first characteristic is an instantaneous amplitude or power of the input signal, and the second characteristic is an integrated signal envelope of the input signal.

21. The linear wideband amplifier system as in claim 19, wherein the addressing circuit generates a third index that represents a third characteristic of the digital input signal and corresponds to a third dimension of the multi-dimensional data structure.

22. The linear wideband amplifier system as in claim 21, wherein the third characteristic is a rate of change of the input signal.

23. The linear wideband amplifier system as in claim 19, wherein the addressing circuit comprises an integration filter that generates an integrated signal envelope of the input signal.

24. The linear wideband amplifier system as in claim 19, wherein the addressing circuit comprises a temperature sensor that measures an amplifier transistor die temperature.

25. The linear wideband amplifier system as in claim 19, wherein the compensation parameters stored within the multi-dimensional data structure include IQ modulator correction coefficients that are used by the digital compensation circuit.

26. The linear wideband amplifier system as in claim 19, further comprising an automatic gain control circuit that dynamically adjusts an output of the digital compensation circuit prior to amplification.

27. The linear wideband amplifier system as in claim 19, wherein the adaptive compensation estimator generates the compensation parameters, and stores the compensation parameters in the multi-dimensional data structure, based on a non-real-time analysis of signals corresponding to the wideband input signal and an observed output signal.

28. The linear wideband amplifier system as in claim 27, wherein the adaptive compensation estimator time stamps sets of compensation parameters stored in the multi-dimensional data structure, and updates outdated sets of compensation parameters.

29. The linear wideband amplifier system as in claim 19, wherein the digital compensation circuit is implemented within dedicated hardware.

30. The linear wideband amplifier system as in claim 29, wherein the digital compensation circuit is implemented within application-specific circuitry.

31. The linear wideband amplifier system as in claim 19, wherein the adaptive compensation estimator is implemented by a processor that executes a firmware program.

32. The linear wideband amplifier system as in claim 31, wherein the adaptive compensation estimator is implemented by a general purpose microprocessor.

33. The linear wideband amplifier system as in claim 31, wherein the adaptive compensation estimator is implemented by a digital signal processor.

34. The linear wideband amplifier system as in claim 31, wherein the firmware program is stored within a memory of an application specific integrated circuit in which the digital compensation circuit is implemented within dedicated hardware.

35. A method of predistorting an input signal to an amplifier system to compensate for distortion introduced by the amplifier system, the method comprising:

digitally processing the input signal to generate a plurality of indices, wherein each of the indices corresponds to a different respective characteristic of the input signal;

applying the plurality of indices in combination to a memory to look up a set of predistortion coefficients therefrom; and

digitally predistorting the input signal according to the set of predistortion coefficients to compensate for distortion introduced during amplification;

whereby the input signal is predistorted using a predistortion function that is dependent upon multiple characteristics of the input signal;

wherein the step of digitally processing the input signal to generate a plurality of indices comprises generating a first index that represents an instantaneous characteristic of the input signal, and generating a second index that represents an averaged characteristic of the input signal.

36. The method of claim 35, further comprising generating an additional index based on a current amplifier die temperature, and using the additional index in combination with the set of indices as an address to look up the set of predistortion coefficients from the memory.

37. The method of claim 35, wherein the input signal is a wideband signal.

38. The method of claim 35, wherein input signal has a spectral occupancy that exceeds 0.1% of an RF carrier frequency of the input signal.

39. A system for digitally predistorting a wideband input signal to a power amplifier, comprising:

a multi-dimensional data structure in which each element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal to compensate for nonlinearities in an amplification process;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the input signal, to read sets of compensation parameters from the data structure;

a digital compensation circuit that predistorts the input signal in real time using the compensation parameters read from the multi-dimensional data structure according to the addressing circuit; and

an adaptive estimation component that generates the compensation parameters, and stores the compensation parameters in the multi-dimensional data structure, based on a non-real-time analysis of the wideband input signal and an observed output signal;

whereby a predistortion function applied by the digital compensation circuit is dependent upon the characteristics of the wideband input signal.

40. The system as in claim 39, wherein the adaptive estimation component time stamps sets of compensation parameters stored in the multi-dimensional data structure, and updates outdated sets of compensation parameters.

41. The system as in claim 39, wherein the adaptive estimation component applies at least one of the following classes of algorithms to captured sequences of samples:

LMS, RLS, Kalman.

42. The system as in claim 39, wherein the adaptive estimation component generates compensation parameters for each of a plurality of digital compensation circuits, wherein each digital compensation circuit predistorts an input signal along a respective amplification chain of an antenna array system.

43. A system for digitally predistorting a wideband input signal to a power amplifier, comprising:

a multi-dimensional data structure in which each element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal to compensate for nonlinearities in an amplification process;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the input signal, to read sets of compensation parameters from the data structure; and

a digital compensation circuit that predistorts the input signal in real time using the compensation parameters read from the multi-dimensional data structure according to the addressing circuit, wherein the digital compensation circuit comprises a quasi-static filter that is cascaded with a dynamic filter, wherein coefficients of the dynamic filter are updated more frequently than coefficients of the quasi-static filter;

whereby a predistortion function applied by the digital compensation circuit is dependent upon the characteristics of the wideband input signal.

44. A system for digitally predistorting a wideband input signal to a power amplifier, comprising:

a multi-dimensional data structure in which each element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal to compensate for nonlinearities in an amplification process;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the input signal, to read sets of compensation parameters from the data structure, wherein the addressing circuit generates a third index using an output of a temperature sensor that measures a transistor die temperature of the power amplifier, and uses the third index in combination with first and second indexes to look up sets of compensation parameters from the multi-dimensional data structure; and

a digital compensation circuit that predistorts the input signal in real time using the compensation parameters read from the multi-dimensional data structure according to the addressing circuit;

whereby a predistortion function applied by the digital compensation circuit is dependent upon the characteristics of the wideband input signal.

45. A system for digitally predistorting a wideband input signal to a power amplifier, comprising:

a multi-dimensional data structure in which each element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal to compensate for nonlinearities in an amplification process, wherein the wideband input signal has a spectral occupancy that exceeds 0.1% of the input signal'"'"'s RF carrier frequency;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the input signal, to read sets of compensation parameters from the data structure; and

a digital compensation circuit that predistorts the input signal in real time using the compensation parameters read from the multi-dimensional data structure according to the addressing circuit;

whereby a predistortion function applied by the digital compensation circuit is dependent upon the characteristics of the wideband input signal.

46. A linear wideband amplifier system, comprising:

a nonlinear amplification chain along which a wideband input signal is upconverted and amplified for transmission;

a multi-dimensional data structure in which each storage element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the wideband input signal, to read sets of compensation parameters from the data structure for use;

a digital compensation circuit that predistorts the wideband input signal, prior to processing along the amplification chain, using the sets of compensation parameters read from the multi-dimensional data structure, to compensate for nonlinearities in the amplification chain, wherein the digital compensation circuit comprises a quasi-static filter that is cascaded with a dynamic filter, wherein coefficients of the dynamic filter are updated more frequently than coefficients of the quasi-static filter; and

an adaptive compensation estimator that generates the sets of compensation parameters stored in the multi-dimensional data structure based on a non-real-time analysis of signals within the amplifier system.

47. A system for digitally predistorting a wideband input signal to a power amplifier, comprising:

a multi-dimensional data structure in which each element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal to compensate for nonlinearities in an amplification process;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the input signal, to read sets of compensation parameters from the data structure; and

a digital compensation circuit that predistorts the input signal in real time using the compensation parameters read from the multi-dimensional data structure according to the addressing circuit, wherein the digital compensation circuit comprises a finite impulse response (FIR) filter for which coefficient sets are read from the multi-dimensional data structure;

wherein the digital compensation circuit comprises a first digital filter that processes the input signal and comprises a second digital filter that independently processes a second order multiple of the input signal, wherein outputs of at least the first and second digital filters are summed to form a compensated input signal;

whereby a predistortion function applied by the digital compensation circuit is dependent upon the characteristics of the wideband input signal.

48. The system as in claim 47, wherein the multi-dimensional data structure stores sets of coefficients for the first and second digital filters.

49. A system for digitally predistorting a wideband input signal to a power amplifier, comprising:

a multi-dimensional data structure in which each element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal to compensate for nonlinearities in an amplification process;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the input signal, to read sets of compensation parameters from the data structure; and

a digital compensation circuit that predistorts the input signal in real time using the compensation parameters read from the multi-dimensional data structure according to the addressing circuit, wherein the digital compensation circuit comprises a finite impulse response (FIR) filter for which coefficient sets are read from the multi-dimensional data structure;

whereby a predistortion function applied by the digital compensation circuit is dependent upon the characteristics of the wideband input signal;

and wherein the digital compensation circuit comprises;

means for generating higher order multiples of the input signal;

means for independently filtering the input signal and each higher order multiple of the input signal; and

means for combining the input signal and the higher order multiples of the input signal after filtering to form a compensated input signal.

50. A linear wideband amplifier system, comprising:

a nonlinear amplification chain along which a wideband input signal is upconverted and amplified for transmission;

a multi-dimensional data structure in which each storage element stores a set of compensation parameters, including filter coefficients, for predistorting the wideband input signal;

an addressing circuit that generates indexes for each of the multiple dimensions of the data structure, based at least upon characteristics of the wideband input signal, to read sets of compensation parameters from the data structure for use;

a digital compensation circuit that predistorts the wideband input signal, prior to processing along the amplification chain, using the sets of compensation parameters read from the multi-dimensional data structure, to compensate for nonlinearities in the amplification chain;

an adaptive compensation estimator that generates the sets of compensation parameters stored in the multi-dimensional data structure based on a non-real-time analysis of signals within the amplifier system, wherein the adaptive compensation estimator generates the compensation parameters, and stores the compensation parameters in the multi-dimensional data structure, based on a non-real-time analysis of signals corresponding to the wideband input signal and an observed output signal; and

a feedback circuit that generates a digital observation signal which represents an output of the amplification chain, and provides the digital observation signal to the adaptive compensation estimator.

51. The linear wideband amplifier system as in claim 50, wherein the adaptive compensation estimator time stamps sets of compensation parameters stored in the multi-dimensional data structure, and updates outdated sets of compensation parameters.