Arbitrary waveform predistortion table generation

• US 20060071711A1
• Filed: 06/29/2005
• Published: 04/06/2006
• Est. Priority Date: 10/06/2004
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Brandt, Per-Olof, Persson, Jonas
• Granted Patent: US 7,330,073 B2
• Time in Patent Office: Days
• US Class Current: 330/149
• CPC Class Codes: H03F 1/0211 with control of the supply voltage or current
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3288 to compensate phase shift as a function of the amplitude
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion

Abstract

Predistortion that will compensate for distortion introduced by a power amplifier circuit is determined by applying a time-varying reference signal to the power amplifier circuit, wherein at each moment the time-varying reference signal has a reference amplitude and a reference phase. A corresponding output signal supplied by the power amplifier circuit is measured, wherein at each moment the output signal has a measured amplitude and a measured phase. Amplitude predistortion is determined by comparing the reference amplitude with the measured amplitude, and phase predistortion is determined by comparing the reference phase with the measured phase. A relationship between the phase predistortion and the reference amplitude is determined such that, for any value of the reference amplitude, a corresponding value of the phase predistortion is identified.

Claims

1. A method of determining predistortion that will compensate for distortion introduced by a power amplifier circuit, the method comprising:

applying a time-varying reference signal to the power amplifier circuit, wherein at each moment the time-varying reference signal has a reference amplitude and a reference phase;

measuring a corresponding output signal supplied by the power amplifier circuit, wherein at each moment the output signal has a measured amplitude and a measured phase;

determining amplitude predistortion by comparing the reference amplitude with the measured amplitude;

determining phase predistortion by comparing the reference phase with the measured phase; and

determining a relationship between the phase predistortion and the reference amplitude such that, for any value of the reference amplitude, a corresponding value of the phase predistortion is identified.

2. The method of claim 1, wherein the reference amplitude is a ramp waveform, and the reference phase is a constant.

3. The method of claim 1, wherein the reference amplitude is a triangle waveform, and the reference phase is a constant.

4. The method of claim 1, wherein the reference signal has both varying amplitude and varying phase.

5. The method of claim 1, wherein:

the amplitude predistortion is associated with a range of measured amplitude values; and

the method further comprises extracting representative points from the amplitude predistortion by performing;

dividing the range of measured amplitude values into a number of intervals; and

for each of the intervals, determining an average amplitude predistortion value and using the average amplitude predistortion value as the amplitude predistortion value associated with a measured amplitude value at the center of the interval.

6. The method of claim 5, further comprising:

interpolating between two average amplitude predistortion values respectively associated with adjacent first and second intervals to determine an amplitude predistortion value associated with a measured amplitude value that is in-between the centers of the first and second intervals.

7. The method of claim 1, wherein:

the phase predistortion is associated with a range of reference amplitude values; and

the method further comprises extracting representative points from the phase predistortion by performing;

dividing the range of reference amplitude values into a number of intervals; and

for each of the intervals, determining an average phase predistortion value and using the average phase predistortion value as the phase predistortion value associated with a reference amplitude value at the center of the interval.

8. The method of claim 7, further comprising:

interpolating between two average phase predistortion values respectively associated with adjacent first and second intervals to determine a phase predistortion value associated with a reference amplitude value that is in-between the centers of the first and second intervals.

9. The method of claim 1, comprising:

prior to comparing the reference amplitude with the measured amplitude, performing;

identifying one or more dips in the reference amplitude;

identifying one or more dips in the measured amplitude; and

aligning the reference amplitude and the measured amplitude with respect to time by shifting the reference amplitude and the measured amplitude relative to one another by an amount that best aligns the dips of the reference amplitude with corresponding dips of the measured amplitude.

10. The method of claim 1, comprising:

prior to comparing the reference phase with the measured phase, performing;

identifying one or more dips in the reference phase;

identifying one or more dips in the measured phase; and

aligning the reference phase and the measured phase with respect to time by shifting the reference phase and the measured phase relative to one another by an amount that best aligns the dips of the reference phase with corresponding dips of the measured phase.

11. The method of claim 1, comprising:

prior to comparing the reference amplitude with the measured amplitude, aligning the reference amplitude and the measured amplitude with respect to time by an amount that minimizes a spread between a plurality of amplitude predistortion values associated with any one amplitude reference value.

12. The method of claim 11, comprising:

determining the spread by determining the difference between a minimum one of the amplitude predistortion values associated with the amplitude reference value and a maximum one of the amplitude predistortion values associated with the amplitude reference value.

13. The method of claim 11, comprising:

determining a set of highest valued ones of the amplitude predistortion values associated with the amplitude reference value;

determining a set of lowest valued ones of the amplitude predistortion values associated with the amplitude reference value;

determining a noise reduced maximum value of the amplitude predistortion values by averaging the set of highest valued ones of the amplitude predistortion values associated with the amplitude reference value;

determining a noise reduced minimum value of the amplitude predistortion values by averaging the set of lowest valued ones of the amplitude predistortion values associated with the amplitude reference value; and

determining the spread by determining the difference between the noise reduced minimum value of the amplitude predistortion values and the noise reduced maximum value of the amplitude predistortion values.

14. The method of claim 1, comprising:

prior to comparing the reference phase with the measured phase, aligning the reference phase and the measured phase with respect to time by an amount that minimizes a spread between a plurality of phase predistortion values associated with any one amplitude reference value.

15. The method of claim 14, comprising:

determining the spread by determining the difference between a minimum one of the phase predistortion values associated with the amplitude reference value and a maximum one of the phase predistortion values associated with the amplitude reference value.

16. The method of claim 14, comprising:

determining a set of highest valued ones of the phase predistortion values associated with the amplitude reference value;

determining a set of lowest valued ones of the phase predistortion values associated with the amplitude reference value;

determining a noise reduced maximum value of the phase predistortion values by averaging the set of highest valued ones of the phase predistortion values associated with the amplitude reference value;

determining a noise reduced minimum value of the phase predistortion values by averaging the set of lowest valued ones of the phase predistortion values associated with the amplitude reference value; and

determining the spread by determining the difference between the noise reduced minimum value of the phase predistortion values and the noise reduced maximum value of the phase predistortion values.

17. An apparatus for determining predistortion that will compensate for distortion introduced by a power amplifier circuit, the apparatus comprising:

logic that applies a time-varying reference signal to the power amplifier circuit, wherein at each moment the time-varying reference signal has reference amplitude and a reference phase;

logic that measures a corresponding output signal supplied by the power amplifier circuit, wherein at each moment the output signal has a measured amplitude and a measured phase;

logic that determines amplitude predistortion by comparing the reference amplitude with the measured amplitude;

logic that determines phase predistortion by comparing the reference phase with the measured phase; and

logic that determines a relationship between the phase predistortion and the reference amplitude such that, for any value of the reference amplitude, a corresponding value of the phase predistortion is identified.

18. The apparatus of claim 17, wherein the reference amplitude is a ramp waveform, and the reference phase is a constant.

19. The apparatus of claim 17, wherein the reference amplitude is a triangle waveform, and the reference phase is a constant.

20. The apparatus of claim 17, wherein the reference signal has both varying amplitude and varying phase.

21. The apparatus of claim 17, wherein:

the amplitude predistortion is associated with a range of measured amplitude values; and

the apparatus further comprises logic that extracts representative points from the amplitude predistortion by performing;

dividing the range of measured amplitude values into a number of intervals; and

for each of the intervals, determining an average amplitude predistortion value and using the average amplitude predistortion value as the amplitude predistortion value associated with a measured amplitude value at the center of the interval.

22. The apparatus of claim 21, further comprising:

logic that interpolates between two average amplitude predistortion values respectively associated with adjacent first and second intervals to determine an amplitude predistortion value associated with a measured amplitude value that is in-between the centers of the first and second intervals.

23. The apparatus of claim 17, wherein:

the phase predistortion is associated with a range of reference amplitude values; and

the apparatus further comprises logic that extracts representative points from the phase predistortion by performing;

dividing the range of reference amplitude values into a number of intervals; and

for each of the intervals, determining an average phase predistortion value and using the average phase predistortion value as the phase predistortion value associated with a reference amplitude value at the center of the interval.

24. The apparatus of claim 23, further comprising:

logic that interpolates between two average phase predistortion values respectively associated with adjacent first and second intervals to determine a phase predistortion value associated with a reference amplitude value that is in-between the centers of the first and second intervals.

25. The apparatus of claim 17, comprising:

logic that, prior to comparing the reference amplitude with the measured amplitude, performs;

identifying one or more dips in the reference amplitude;

identifying one or more dips in the measured amplitude; and

aligning the reference amplitude and the measured amplitude with respect to time by shifting the reference amplitude and the measured amplitude relative to one another by an amount that best aligns the dips of the reference amplitude with corresponding dips of the measured amplitude.

26. The apparatus of claim 17, comprising:

logic that, prior to comparing the reference phase with the measured phase, performs;

identifying one or more dips in the reference phase;

identifying one or more dips in the measured phase; and

aligning the reference phase and the measured phase with respect to time by shifting the reference phase and the measured phase relative to one another by an amount that best aligns the dips of the reference phase with corresponding dips of the measured phase.

27. The apparatus of claim 17, comprising:

logic that, prior to comparing the reference amplitude with the measured amplitude, aligns the reference amplitude and the measured amplitude with respect to time by an amount that minimizes a spread between a plurality of amplitude predistortion values associated with any one amplitude reference value.

28. The apparatus of claim 27, comprising:

logic that determines the spread by determining the difference between a minimum one of the amplitude predistortion values associated with the amplitude reference value and a maximum one of the amplitude predistortion values associated with the amplitude reference value.

29. The apparatus of claim 27, comprising:

logic that determines a set of highest valued ones of the amplitude predistortion values associated with the amplitude reference value;

logic that determines a set of lowest valued ones of the amplitude predistortion values associated with the amplitude reference value;

logic that determines a noise reduced maximum value of the amplitude predistortion values by averaging the set of highest valued ones of the amplitude predistortion values associated with the amplitude reference value;

logic that determines a noise reduced minimum value of the amplitude predistortion values by averaging the set of lowest valued ones of the amplitude predistortion values associated with the amplitude reference value; and

logic that determines the spread by determining the difference between the noise reduced minimum value of the amplitude predistortion values and the noise reduced maximum value of the amplitude predistortion values.

30. The apparatus of claim 17, comprising:

logic that, prior to comparing the reference phase with the measured phase, aligns the reference phase and the measured phase with respect to time by an amount that minimizes a spread between a plurality of phase predistortion values associated with any one amplitude reference value.

31. The apparatus of claim 30, comprising:

logic that determines the spread by determining the difference between a minimum one of the phase predistortion values associated with the amplitude reference value and a maximum one of the phase predistortion values associated with the amplitude reference value.

32. The apparatus of claim 30, comprising:

logic that determines a set of highest valued ones of the phase predistortion values associated with the amplitude reference value;

logic that determines a set of lowest valued ones of the phase predistortion values associated with the amplitude reference value;

logic that determines a noise reduced maximum value of the phase predistortion values by averaging the set of highest valued ones of the phase predistortion values associated with the amplitude reference value;

logic that determines a noise reduced minimum value of the phase predistortion values by averaging the set of lowest valued ones of the phase predistortion values associated with the amplitude reference value; and

logic that determines the spread by determining the difference between the noise reduced minimum value of the phase predistortion values and the noise reduced maximum value of the phase predistortion values.

33. A machine storage medium having stored therein a set of program instructions for determining predistortion that will compensate for distortion introduced by a power amplifier circuit, the set of program instructions causing a processor and associated logic to perform:

applying a time-varying reference signal to the power amplifier circuit, wherein at each moment the time-varying reference signal has a reference amplitude and a reference phase;

measuring a corresponding output signal supplied by the power amplifier circuit, wherein at each moment the output signal has a measured amplitude and a measured phase;

determining amplitude predistortion by comparing the reference amplitude with the measured amplitude;

determining phase predistortion by comparing the reference phase with the measured phase; and

determining a relationship between the phase predistortion and the reference amplitude such that, for any value of the reference amplitude, a corresponding value of the phase predistortion is identified.