Methods of optimising power amplifier efficiency and closed-loop power amplifier controllers

• US 6,703,897 B2
• Filed: 12/26/2001
• Issued: 03/09/2004
• Est. Priority Date: 12/26/2001
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: O'Flaherty, Martin J., Nemish, Roman N., Tholl, David M., Neilson, Gordon B., Norman, Charles E.
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): NGUYEN, KHAI M
• Application Number:
  US10/035,879
• Publication Number:
  US 20030117215A1
• Time in Patent Office: 804 Days
• Field of Search: 330/107, 330/136, 330/149, 330/129, 330/285, 455/126
• US Class Current: 330/149
• CPC Class Codes: H03F 1/0244 Stepped control
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3282 Acting on the phase and the amplitude of the input signal
• CPC Class Codes: H03F 2200/102 A non-specified detector of a signal envelope being used in an amplifying circuit

Abstract

A significant part of the cost of a base station in the cellular mobile radio system is the power amplifier. Thus it is desirable to maximise usage of a power amplifier and in particular to gain the best power output from the amplifier or to improve its efficiency. Such power amplifiers, however, must operate within strict spectral boundaries and thus power amplifiers are typically over-specified in order to ensure that the spectral requirements are met. By measuring the output of the amplifier and determining distortion factors and then adaptively adjusting the operating characteristics of the amplifier, the degree of over-specification of the amplifier required may be reduced with consequent cost and environmental savings.

Claims

1. A closed-loop power amplifier distortion controller comprising:

—

(a) a closed-loop pre-distortion control arranged to apply pre-distortion to the amplifier input signal automatically based on a measured predetermined output characteristic;

(b) measuring means operable to measure the amount of applied pre-distortion which is representative of distortion introduced by the amplifier; and

(c) control means for adjusting an operating parameter of the amplifier responsive to the amount of applied pre-distortion.

2. A controller according to claim 1, wherein the said predetermined output characteristic is phase distortion.

3. A controller according to claim 1, wherein the said predetermined output characteristic is amplitude distortion.

4. A controller according to claim 1, wherein the said predetermined output characteristic is the frequency spectrum.

5. A controller according to claim 1, wherein the said operating parameter is the output voltage of a power supply arranged to supply power to the power amplifier.

6. A controller according to claim 1, wherein the said operating parameter is the gain of the power amplifier.

7. A method of optimising efficiency in a power amplifier comprising:

(a) applying pre-distortion to the amplifier input signal automatically based on a measured output characteristic,

(b) measuring the amount at applied pre-distortion which is representative of distortion introduced by the amplifier, and

(c) controlling an operational parameter of the amplifier responsive to the amount of applied pre-distortion.

8. A method according to claim 7, further comprising processing the output characteristic measure to determine a gradient of that measure against change in the operational characteristic, and periodically adjusting the operational parameter to substantially achieve a desired value for the said gradient.

9. A method according to claim 8 wherein the measured output characteristic is phase distortion and wherein the desired gradient approaches infinity which is representative of clipping distortion in the amplifier.

10. A method according to claim 8 wherein the measured output characteristic is amplitude distortion and wherein the desired gradient approaches infinity which is representative of clipping distortion in the amplifier.

11. A method according to claim 8 wherein the operational parameter is the voltage of the electrical supply for the power amplifier.

12. A method according to claim 8 wherein the operational parameter is the gain of the amplifier.

13. A method according to claim 7, further comprising comparing the output characteristic measure against a predetermined threshold and periodically adjusting the operational parameter to maintain the measured output characteristic on a desired side of the said threshold.

14. A method according to claim 13 wherein the output characteristic measure is the frequency spectrum of the output and the threshold is a predetermined spectral mask.

15. A method according to claim 13, wherein the output characteristic measure is the waveform quality of the output.

16. A method according to claim 13, wherein the output characteristic measure is the error vector magnitude.

17. A method according to claim 13, wherein the output characteristic measure is code domain noise in the output.

18. A base station for a radio network including:

—

(a) a power amplifier, and

(b) a closed-loop power amplifier distortion controller including a closed-loop pre-distortion control arranged to apply pre-distortion to the amplifier input signal automatically based on a measured predetermined output characteristic;

measuring means operable to measure the amount of applied pre-distortion which is representative of distortion introduced by the amplifier; and

control means for adjusting an operating parameter of the amplifier responsive to the amount of applied pre-distortion.

19. A wireless communications network including a base station having:

—

(a) a power amplifier, and

(b) a closed-loop power amplifier distortion controller including a closed-loop pre-distortion control arranged to apply pre-distortion to the amplifier input signal automatically based on a measured predetermined output characteristic;

measuring means operable to measure the amount of applied pre-distortion which is representative of distortion introduced by the amplifier, and control means for adjusting an operating parameter of the amplifier responsive to the amount of applied pre-distortion.