LINEARIZATION OF A TRANSMIT AMPLIFIER

• US 20120263256A1
• Filed: 05/25/2012
• Published: 10/18/2012
• Est. Priority Date: 02/15/2006
• Status: Active Grant

• Current Assignee: Khurram Waheed, Oren E. Eliezer, Robert B. Staszewski, Sameh S. Rezeq
• Original Assignee: Khurram Waheed, Oren E. Eliezer, Robert B. Staszewski, Sameh S. Rezeq
• Inventors: Waheed, Khurram, Staszewski, Robert B., Rezeq, Sameh S., Eliezer, Oren E.
• Granted Patent: US 9,020,454 B2
• Time in Patent Office: Days
• US Class Current: 375/296
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion

Abstract

An apparatus and method of linearization of a digitally-controlled pre-power amplifier (DPA) and RF power amplifier (PA) for performing predistortion calibration to compensate for nonlinearlities in the DPA and PA circuits. A predistortion look up table (LUT) stores measured distortion compensation data that is applied to the TX data before being input to the digital-to-frequency converter (DFC), DPA and PA. The on-chip receiver, which is normally inactive during the TX burst in a half-duplex operation, demodulates the RF PA output and uses the digital I/Q RX outputs to perform calibration of the TX pre-distortion tables. A sample of the RF output signal is provided to the receiver chain. While the PA (DPA) code is increasing (or decreasing), the amplitude and phase of the recovered I/Q samples are used to determine the instantaneous value of the AM/AM and AM/PM pre-distortion from which an update to the predistortion tables may be computed.

Claims

1. (canceled)

4. A method of linearization of a transmit amplifier, said method comprising the steps of:

scanning a plurality of power amplifier codes;

generating a transmit amplifier output signal in accordance with each code scanned; and

determining one or more predistortion values in accordance with said transmit amplifier output signal; and

wherein said step of determining comprises the step of inputting said transmit amplifier output signal to receiver operative to demodulate said transmit amplifier output signal.

2. The method according to claim 4, wherein said step of scanning comprises ramping said plurality of codes either up or down.

3. The method according to claim 4, wherein said step of scanning comprises using codes corresponding to the amplitude modulation waveform used during a transmitted payload of data.

5. The method according to claim 4, wherein said predistortion values comprises AM/AM and AM/PM predistortion values.

7. The method according to claim 4, wherein said step of determining comprises incorporating information from one or more on-chip sensors in the calculation of said predistortion values.

6. A method of linearization of a transmit amplifier, said method comprising the steps of:

scanning a plurality of power amplifier codes;

generating a transmit amplifier output signal in accordance with each code scanned; and

determining one or more predistortion values in accordance with said transmit amplifier output signal;

wherein said transmit amplifier comprises a digitally controlled power amplifier.

8. A method of compensating for predistortion of a power amplifier, said method comprising the steps of

scanning a plurality of power amplifier codes;

generating a power amplifier output signal in accordance with each code scanned;

providing controlled leakage of said power amplifier output signal to a receiver chain operative to demodulate said power amplifier output signal to yield a demodulated signal therefrom;

calculating amplitude and phase distortion values in accordance with said demodulated signal; and

calibrating a predistortion table with said amplitude and phase distortion values.

9. The method according to claim 8, wherein said receiver chain is co-located on-chip with a transmitter operative to generate said power amplifier output signal.

10. The method according to claim 8, wherein said step of scanning comprises the step of applying a ramp up or ramp down signal to a transmitter circuit.

11. The method according to claim 8, wherein said step of calibrating comprises the step of storing said amplitude and phase distortion values in a predistortion look up table (LUT).

12. The method according to claim 8, wherein said step of generating a transmit amplifier output signal is performed during a power ramp up or ramp down of a GGE burst.

13. The method according to claim 8, wherein said step of generating a power amplifier output signal is performed during the payload of a burst having a known waveform of varying amplitude.

14. The method according to claim 8, wherein said power amplifier comprises a combination of digitally controlled pre-power amplifier and radio frequency (RF) power amplifier.

15. A method of predistortion calibration of a power amplifier, said method comprising the steps of

stepping through a dynamic range of codes of said power amplifier;

inputting each code to a transmit chain comprising a predistortion look up table (LUT) of transmit amplifier predistortion values to generate a radio frequency (RF) output signal in response thereto;

demodulating said RF output signal to yield a demodulated signal;

calculating an instantaneous correction to the predistortion values stored in said predistortion LUT in accordance with said demodulated signal; and

updating the contents of said predistortion LUT in accordance with said calculated instantaneous correction.

16. The method according to claim 15, wherein said step of stepping is performed during the ramp up portion of a GSM/GPRS/EDGE (GGE) burst transmission.

17. The method according to claim 15, wherein said step of stepping is performed during the ramp down portion of a GSM/GPRS/EDGE (GGE) burst transmission.

18. The method according to claim 15, wherein said step of demodulating is performed utilizing a receiver chain co-located on-chip with said transmit chain.

19. The method according to claim 15, wherein said predistortion values comprise AM/AM and AM/PM predistortion values.

20. The method according to claim 15, wherein said step of updating comprises the steps of:

reading the predistortion values currently stored in said predistortion LUT;

applying said instantaneous correction to the predistortion values read from said predistortion LUT to yield corrected predistortion values thereby; and

saving said corrected predistortion values back into said predistortion LUT.

21. The method according to claim 20, further comprising the step of interpolating the updated contents of said predistortion LUT for any missing correction values.

22. The method according to claim 15, wherein said step of updating comprises the steps of:

reading the predistortion values currently stored in said predistortion LUT;

applying said instantaneous correction to the predistortion values read from said predistortion LUT to yield filtered corrected predistortion values; and

saving said corrected predistortion values back into said predistortion LUT.

23. The method according to claim 22, wherein said filtered corrected predistortion values are generated by applying a moving average filter to a plurality of instantaneous correction values.

24. The method according to claim 22, wherein said filtered corrected predistortion values are generated by applying an infinite impulse response (IIR) filter to a plurality of instantaneous correction values.

25. The method according to claim 22, wherein said filtered corrected predistortion values are generated by applying an auto-regressive moving average (ARMA) filter to a plurality of instantaneous correction values.

26. The method according to claim 22, wherein said filtered corrected predistortion values are generated by applying a nonlinear threshold function permitting said step of correcting to ignore inputs exceeding a predetermined range of expected values caused by strong interference induced into the receiver.

27. The method according to claim 15, wherein said power amplifier comprises a combination of digitally controlled pre-power amplifier and radio frequency (RF) power amplifier.

28. An apparatus for calibrating predistortion of a digitally controlled power amplifier (DPA), comprising:

circuitry for stepping through a range of codes of said DPA;

a transmit chain comprising a predistortion look up table (LUT) adapted to store a plurality of amplifier predistortion values, said transmit chain operative to generate a radio frequency (RF) output signal in response to each code;

circuitry for coupling said RF output signal to a receiver chain, said receive chain operative to demodulate said RF output signal to generate a demodulated signal therefrom;

circuitry for calculating corrections to the predistortion values stored in said predistortion LUT in accordance with said recovered I and Q values; and

update circuitry for updating the contents of said predistortion LUT in accordance with said calculated corrections.

29. The apparatus according to claim 28, wherein said circuitry for calculating comprises circuitry for incorporating information from one or more on-chip sensors in the calculation of said predistortion values.

30. The apparatus according to claim 29, wherein said on-chip sensor comprises a temperature sensor operative to generate temperature information.

31. The apparatus according to claim 28, wherein said circuitry for stepping comprises means for generating said range of codes during the ramp up portion of a GSM/GPRS/EDGE (GGE) burst transmission.

32. The apparatus according to claim 28, wherein said circuitry for stepping comprises circuitry for generating said range of codes during the ramp down portion of a GSM/GPRS/EDGE (GGE) burst transmission.

33. The apparatus according to claim 28, wherein said receive chain is co-located on-chip with said transmit chain.

34. The apparatus according to claim 28, wherein said predistortion values comprise AM/AM and AM/PM predistortion values.

35. The apparatus according to claim 28, wherein said update circuitry comprises circuitry for applying a filter function to said corrections.

36. The apparatus according to claim 35, wherein said filter function comprises a moving average function.

37. The apparatus according to claim 35, wherein said filter function comprises an infinite impulse response (IIR) filter function.

38. The apparatus according to claim 35, wherein said filter function comprises an auto-regressive moving average (ARMA) filter function.

39. The apparatus according to claim 35, wherein said filter function comprises a threshold function that would determine whether the computed update exceeds a predefined magnitude.

40. The apparatus according to claim 35, wherein said range of codes are stepped through, corresponding correction values calculated and said predistortion LUT updated during a time wherein said transmit chain is inactive.

41-43. -43. (canceled)