Method and apparatus for reducing dynamic range of a power amplifier

• US 20040192369A1
• Filed: 08/08/2002
• Published: 09/30/2004
• Est. Priority Date: 08/08/2002
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Nilsson, Magnus
• Granted Patent: US 6,892,057 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: H03C 3/0925 applying frequency modulation at the divider in the feedback loop
• CPC Class Codes: H03C 3/0933 using fractional frequency division in the feedback loop of the phase locked loop
• CPC Class Codes: H03C 5/00 Amplitude modulation and angle modulation produced simultaneously or at will by the same modulating signal H03C7/00 takes precedence

Abstract

An output-power threshold is selected such that one or more signal requirements is not outside a pre-determined range when output power of a polar transmitter is less than the output-power threshold. A determination is made whether the output power is less than the threshold. In response to a determination that the output power is less than the threshold, amplitude modulation of a polar signal transmitted by the polar transmitter is disabled. When the output power meets or exceeds the output-power threshold, the polar signal transmitted by the polar transmitter is both amplitude and phase modulated.

Claims

1. A method of operating a polar transmitter, the method comprising:

transmitting first information at a first output power greater than an output-power threshold, wherein the first information is amplitude and phase modulated;

transmitting second information at a second output power not exceeding the output-power threshold, wherein the second information is only phase modulated; and

wherein the output-power threshold is selected such that at least one signal requirement is not outside a pre-determined range when the output power does not exceed the output power threshold.

2. The method of claim 1, wherein the at least one signal requirement comprises an error vector magnitude value.

3. The method of claim 2, wherein the pre-determined range is 0-17.5%.

4. The method of claim 1, wherein the at least one signal requirement comprises an adjacent channel leakage ratio.

5. The method of claim 1, wherein the steps are performed in the order listed.

6. The method of claim 1, wherein the at least one signal requirement comprises a measure of information quality.

7. The method of claim 1, further comprising, in response to the output power not exceeding the pre-determined output-power threshold, running a power amplifier in a saturated mode and controlling the output power by varying a bias level of the power amplifier.

8. The method of claim 1, further comprising, in response to the output power not exceeding the pre-determined output-power threshold, running a power amplifier in a linear mode and controlling the output power by a variable gain amplifier.

9. The method of claim 1, further comprising:

decreasing the output power toward the output-power threshold;

decreasing an effective modulation depth linearly in relation to the decrease in the output power;

responsive to the output power not exceeding the output-power threshold, performing the step of transmitting the second information.

10. A method of transmitting a polar signal, the method comprising:

selecting an output-power threshold, the output-power threshold being selected such that at least one signal requirement is not outside a pre-determined range when output power is less than the output-power threshold;

determining whether the output power is less than the threshold; and

in response to a determination that the output power is less than the threshold, disabling amplitude modulation of the polar signal.

11. The method of claim 10, wherein the at least one signal requirement comprises an error vector magnitude value.

12. The method of claim 11, wherein the pre-determined range is 0-17.5%

13. The method of claim 10, wherein the at least one signal requirement comprises an adjacent channel leakage ratio.

14. The method of claim 10, further comprising, in response to a determination that the output power is not less than the threshold, enabling amplitude modulation of the polar signal.

15. The method of claim 10, wherein the at least one signal requirement comprises a measure of information quality.

16. The method of claim 10, further comprising, in response to the determination that the output power is less than the pre-determined output-power threshold, running a power amplifier in a saturated mode and controlling the output power by varying a bias level of the power amplifier.

17. The method of claim 10, further comprising, in response to the determination that the output power is less than the pre-determined output-power threshold, running a power amplifier in a linear mode and controlling the output power by a variable gain amplifier.

18. The method of claim 10, further comprising:

decreasing the output power toward the output-power threshold; and

decreasing an effective modulation depth linearly in relation to the decrease in the output power

19. An apparatus comprising:

a modulator, wherein the modulator is adapted to perform phase modulation of an input signal, thereby yielding a phase-modulated input signal;

a power amplifier adapted to perform amplitude modulation of the phase-modulated input signal in response to output power of the apparatus exceeding a pre-determined output-power threshold; and

wherein the output-power threshold is selected such that at least one signal requirement is not outside a pre-determined range when the output-power threshold is not exceeded.

20. The apparatus of claim 19, wherein the at least one signal requirement comprises an error vector magnitude value

21. The apparatus of claim 20, wherein the pre-determined range is 0-17.5%.

22. The apparatus of claim 19, wherein the at least one signal requirement comprises an adjacent channel leakage ratio.

23. The apparatus of claim 19, wherein the at least one signal requirement comprises a measure of information quality.

24. The apparatus of claim 19, wherein, when the output power does not exceed the pre-determined output-power threshold, the power amplifier is run in a saturated mode and the output power is controlled by varying a bias level of the power amplifier.

25. The apparatus of claim 19, wherein, when the output power does not exceed the pre-determined output-power threshold, the power amplifier is run in a linear mode and the output power is controlled by a variable gain amplifier.

26. The apparatus of claim 19, wherein:

when the output power is within a pre-determined range of a lower bound of a dynamic range of the apparatus and is decreased toward the output-power threshold, an effective modulation depth is decreased linearly in relation to the decrease in the output power; and

upon the output-power threshold being reached, the power amplifier no longer performs the amplitude modulation.