Type-based baseband predistorter function estimation technique for non-linear circuits

• US 20030184374A1
• Filed: 03/26/2003
• Published: 10/02/2003
• Est. Priority Date: 03/26/2002
• Status: Active Grant

• Current Assignee: Her Majesty The Queen In Right of Canada As Represented By The Minister of National Defence
• Original Assignee: Her Majesty The Queen In Right of Canada As Represented By The Minister of National Defence
• Inventors: Caron, Mario, Huang, Xinping
• Granted Patent: US 6,885,241 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 1/3294 Acting on the real and imaginary components of the input signal
• CPC Class Codes: H03F 2200/102 A non-specified detector of a signal envelope being used in an amplifying circuit
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

This invention is about a novel estimation technique for generating a predistortion function to compensate for the AM-AM and AM-PM non-linear conversion distortions of non-linear power amplifiers or non-linear circuits. Based on the cumulative type of power amplifier output envelope, a non-parametric baseband predistortion function is derived. The non-parametric approach avoids any model mismatch. In addition, the technique does not need to demodulate the input signal. Furthermore, it minimizes the effect of the power amplifier non-linearity and significantly improves the system performance

Claims

1. A method of compensating for non-linear conversion distortions of a circuit comprising the steps of:

(a) providing a reference type information for an input signal being provided to the circuit;

(b) transforming the input signal in a non-linear manner to form an output signal;

(c) sampling a portion of the output signal to provide a plurality of values relating to a parameter thereof, each at a different time;

(d) deriving predistortion information based on the reference type information and the plurality of values ; and

(e) predistorting the input signal being provided to the circuit in dependence upon the predistortion information.

2. A method according to claim 1, wherein the step (d) comprises a step of calculating an output type information based on the plurality of values and wherein the predistortion information is based at least in part on the output type information.

3. A method according to claim 1, wherein the step of (a) comprises the step of sampling to determine the reference type information.

4. A method according to claim 1, wherein the circuit comprises a power amplifier (PA).

5. A method according to claim 1, wherein the circuit consists of a power amplifier (PA).

6. A method according to claim 1, comprising the step of modulating the input signal, where the reference type information is based on a known modulating scheme.

7. A method according to claim 1, comprising the steps of:

mapping of the input signal to form a mapped signal; and

,

pulse shaping of the mapped signal, where the reference type information is based on a known pulse shaping function.

8. A method according to claim 1, comprising the steps of:

mapping the input signal using a known modulation scheme;

pulse shaping the input signal using a known pulse shaping function; and

providing a memory circuit, where a different reference type information is stored for each combination of a known modulation scheme and a known pulse shaping function.

9. A method according to claim 8, comprising the steps of:

providing a lookup table (LUT); and

,

updating the LUT with predistortion data when at least one of the modulation scheme and the pulse shaping function is changed.

10. A method according to claim 1, wherein the reference type information and the output type information are based on a same type.

11. A method according to claim 10, wherein the type based function is a cumulative distribution function (CDF).

12. A method according to claim 10, wherein the type based function is a probability density function (PDF).

13. A method according to claim 1, wherein the non-linear conversion distortion is a result of AM-AM conversion by the non-linear circuit.

14. A method according to claim 1, wherein the non-linear conversion distortions is a result of AM-PM conversion by the non-linear circuit.

15. A method according to claim 1, wherein the output type information comprises at least one of amplitude information and phase information about the output signal envelope.

16. A method according to claim 15, wherein the derived predistortion information from the reference type information comprises at least one of amplitude information and phase information about the input signal.

17. A method according to claim 1, wherein the input signal is mapped to symbols at a predetermined symbol rate and where the step of sampling is performed at a rate that is lower than the predetermined symbol rate.

18. A method according to claim 1, comprising the step of (f) updating the reference type information in dependence upon the output type information having changed as a result of a change in the step of transforming.

19. A method according to claim 18, wherein the steps of (a) through (f) are performed in a transmitter system without disrupting the operation of the transmitter system.

20. A method according to claim 1, wherein the reference type information is dependent upon an input signal modulation scheme.

21. A method according to claim 15, comprising the step of:

providing a power detector, the power detector for detecting the power of the output signal in the step of sampling and where the output type information comprises amplitude information about the output signal envelope.

22. A method according to claim 21, comprising the step of:

providing a complex envelope detector for detecting at least one of the amplitude and phase information in the step of sampling the output signal envelope and where the output type information comprises at least one of amplitude and phase information.

23. A method according to claim 2, wherein the PA has a monotonically increasing and continuous relationship between a signal provided on the input port and a signal provided on the output port up to the output saturation point of the PA.

24. A method according to claim 2, wherein the step of deriving comprises the steps of:

determining a plurality of data values, each data value for mapping a data point along the output type information to a data point along the reference type information; and

,

storing the data values.

25. A method according to claim 24, wherein the step of storing comprises the step of providing a lookup table (LUT) for storing of predistortion data derived from the data values, wherein the data values are stored in the memory circuit.

26. A method according to claim 24, wherein the mapping is non-linear.

27. A method according to claim 1, comprising the step of other than reconstructing of the input signal.

28. A method according to claim 1, comprising the step of other than comparing the input signal to the output signal of the circuit.

29. A method according to claim 1, comprising the step of other than reconstructing an output signal envelope waveform in time.

30. A method according to claim 1, wherein the input signal comprises data within each of a plurality of modulated frequency channels, each channel from the plurality having a different central frequency.

32. A memory circuit according to claim 31, wherein the third set of instruction data comprises a fifth set of instruction data for calculating an output type information based on the plurality of values and wherein the predistortion information is based at least in part on the output type information.

31. A memory circuit for storing data for use with a circuit comprising:

a first set of data relating to a reference type information for an input signal being provided to the circuit;

a second set of instruction data for sampling a portion of the output signal to provide a plurality of values relating to a parameter thereof, each at a different time;

a third set of instruction data for deriving predistortion information based on the reference type information and the plurality of values; and

,

a fourth set of instruction data for predistorting the input signal being provided to the circuit in dependence upon the predistortion information.

33. A circuit comprising:

a memory circuit for storing a reference type information for an input signal being provided to the circuit;

a transforming circuit for transforming the input signal in a non-linear manner to form an output signal;

a sampling circuit for sampling a portion of the output signal to provide a plurality of values relating to a parameter thereof, each at a different time;

a processor for deriving predistortion information based on the reference type information and the plurality of values; and

.

a predistortion circuit for predistorting the input signal being provided to the circuit in dependence upon the predistortion information.

34. A circuit according to claim 33, wherein the processor comprises circuitry for calculating an output type information based on the plurality of values and wherein the predistortion information is based at least in part on the output type information.

35. A method of determining predistortion data for a circuit comprising the steps of:

providing a first memory circuit;

providing a second memory circuit;

providing a reference type information stored in the second memory circuit;

providing an input signal to an input port of the circuit;

measuring an output type information at an output port of the circuit after having the input signal propagate through the circuit;

storing the output type information in the second memory circuit;

processing the reference type information and the output type information to derive the predistortion data that defines inverse input output characteristics of the circuit; and

,

storing at least a portion of the predistortion data in the first memory circuit.

36. A method according to claim 35, wherein the first memory circuit comprises a lookup table (LUT).

37. A method according to claim 35, wherein the step of processing comprises the steps of:

determining a conditional histogram of a linear circuit output phase for a predetermined input signal amplitude;

determining a conditional histogram of the non-linear circuit output phase for a predetermined input signal amplitude; and

cross correlating the two determined conditional histograms to derive phase shift information for AM-PM conversion for forming a portion of the predistortion data.

38. A method according to claim 35, comprising the step of processing the input signal with the predistortion data so that the output type information is more representative of the reference type information post processing than before processing.

39. A method according to claim 35, wherein the non-linear system is a transmitter system.

40. A method according to claim 35, wherein the transform of the non-linear circuit provides a unique mapping of an input signal parameter to an output signal parameter, the unique mapping being unique up to the saturation point of the non-linear circuit.

41. A method according to claim 40, wherein the transform is a piecewise continuous function.

42. A method according to claim 40, wherein the transform is a continuous function.

43. A method according to claim 40, wherein the transform is monotonic.