Circuit and method of reducing noise in an RF power amplifier

• US 20050134375A1
• Filed: 12/22/2003
• Published: 06/23/2005
• Est. Priority Date: 12/22/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Westwick, Alan L., Paul, Susanne A.
• Granted Patent: US 7,212,070 B2
• Time in Patent Office: Days
• US Class Current: 330/98
• CPC Class Codes: H03F 1/30 Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in differential amplifiers H03F3/45479
• CPC Class Codes: H03F 3/45941 Controlling the input circuit of the differential amplifier

Abstract

A method and apparatus is used to provide DC stabilization and noise reduction in a multistage power amplifier. The invention uses various feedback techniques to stabilize DC levels, which helps to reduce noise. The invention also uses other techniques to reduce noise, and to reduce the noise transfer function in a power amplifier.

Claims

1. A method of reducing noise in a multi-stage power amplifier, comprising:

providing a first power amplifier stage having an inductance coupled to a first switching device;

coupling a second power amplifier stage to the first power amplifier stage, wherein the second power amplifier stage has an inductance coupled to a second switching device; and

providing a feedback path from the second power amplifier stage to the first power amplifier stage to force the DC levels of the first and second power amplifier stages to be approximately equal.

2. The method of claim 1, wherein the feedback path is provided by an inductor.

3. The method of claim 1, wherein the feedback path is provided by two inductors.

4. The method of claim 1, wherein the feedback path is provided by coupling an inductor to each of the inductances of the first and second power amplifier stages.

5. The method of claim 1, wherein the feedback path is provided by an amplifier.

6. The method of claim 5, wherein the amplifier comprises an op-amp.

7. The method of claim 5, wherein the amplifier is coupled to each of the inductances of the first and second power amplifier stages.

8. The method of claim 1, wherein the feedback path is provided by a resistance.

9. The method of claim 1, wherein the feedback path is provided by a resistor.

10. A method of reducing noise in a multi-stage power amplifier, comprising:

providing a first power amplifier stage having an inductance coupled between first and second switching devices;

providing a second power amplifier stage having an inductance coupled between third and fourth switching devices; and

forming a feedback path from the second power amplifier stage to the first power amplifier stage to force the DC levels of the first and second power amplifier stages to be approximately equal.

11. The method of claim 10, wherein the feedback path is provided by an inductor.

12. The method of claim 10, wherein the feedback path is formed by coupling an inductor to each of the inductances.

13. The method of claim 10, wherein the feedback path is provided by an amplifier.

14. The method of claim 13, wherein the amplifier comprises an an op-amp.

15. The method of claim 10, wherein the feedback path is provided by a resistance.

16. The method of claim 10, wherein the feedback path is provided by a resistor.

17. A multi-stage power amplifier comprising:

a first power amplifier stage having an inductance coupled to a first switching device;

a second power amplifier stage having an inductance coupled to a second switching device; and

a feedback path coupled between the second and first power amplifier stages so as to make the DC levels of the first and second power amplifier stages to be approximately equal.

18. The multi-stage power amplifier of claim 17, wherein the feedback path is formed by coupling an inductor to each of the inductances.

19. The multi-stage power amplifier of claim 17, wherein the feedback path is formed by coupling an amplifier between the second and first power amplifier stages.

20. The multi-stage power amplifier of claim 17, wherein the feedback path is formed by coupling an op-amp between the second and first power amplifier stages.

21. The multi-stage power amplifier of claim 17, wherein the feedback path is provided by a resistance.

22. The multi-stage power amplifier of claim 17, wherein the feedback path is provided by a resistor coupled between the second and first power amplifier stages.

23. A method of reducing noise in a power amplifier, comprising:

providing a power amplifier having one or more inputs and one or more outputs, and having an inductance coupled between first and second switching devices; and

coupling a feedback path between one of the inputs and one of the outputs of the power amplifier.

24. The method of claim 23, wherein the feedback path is formed by a resistance coupled between the one of the inputs and one of the outputs of the power amplifier.

25. The method of claim 24, wherein the resistance is coupled between the gate of the first switching device and the drain of the second switching device.

26. The method of claim 25, further comprising coupling a second resistance between the input and the output of the power amplifier.

27. The method of claim 26, wherein the second resistance is coupled between the gate of the second switching device and the drain of the first switching device.

28. The method of claim 23, wherein the resistance is provided by a resistor.

29. The method of claim 23, wherein the feedback path is formed by an inductance coupled between the one of the inputs and one of the outputs of the power amplifier.

30. A power amplifier having an input and an output comprising:

a first switching device coupled to a first voltage supply node;

a second switching device coupled to a second voltage supply node;

an inductance coupled to between the first and second switching devices; and

a feedback path coupled between the input and the output of the power amplifier.

31. The power amplifier of claim 30, wherein the feedback path comprises a resistor coupled between the input and the output of the power amplifier.

32. The power amplifier of claim 31, wherein the resistor is coupled between the gate of the first switching device and the drain of the second switching device.

33. The power amplifier of claim 32, further comprising a second resistor coupled between the input and the output of the power amplifier.

34. The power amplifier of claim 33, wherein the second resistor is coupled between the gate of the second switching device and the drain of the first switching device.

35. The power amplifier of claim 30, wherein the feedback path comprises an inductance coupled between the input and the output of the power amplifier.

36. A method of reducing noise in a multi-stage power amplifier, comprising:

providing a power amplifier stage having an inductance coupled to a first switching device; and

providing a feedback path from the output of the power amplifier stage to the input of the power amplifier stage to force the DC levels at the input and output of the power amplifier stage to be approximately equal.

37. The method of claim 36, wherein the feedback path is provided by an inductor.

38. The method of claim 36, wherein the feedback path is provided by a resistor.

39. The method of claim 36, wherein the feedback path is provided by an amplifier.

40. The method of claim 39, wherein the amplifier comprises an op-amp.