Methods and apparatus for substantially reducing nonlinear distortion

• US 6,943,628 B2
• Filed: 03/05/2004
• Issued: 09/13/2005
• Est. Priority Date: 03/19/2002
• Status: Expired due to Fees

• Current Assignee: University of North Carolina At Charlotte (University of North Carolina System)
• Original Assignee: University of North Carolina At Charlotte (University of North Carolina System)
• Inventors: Weldon, Thomas Paul
• Primary Examiner(s): Choe, Henry
• Application Number:
  US10/793,999
• Publication Number:
  US 20040251964A1
• Time in Patent Office: 557 Days
• Field of Search: 330/149, 330/151, 330/124.R, 330/295, 375/297, 455/63
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3205 in field-effect transistor amplifiers
• CPC Class Codes: H03F 1/3211 in differential amplifiers
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence

Abstract

Methods and apparatus are provided for substantially reducing and/or canceling nonlinearities of any order in circuits, devices, and systems such as amplifiers and mixers. In particular, methods and apparatus are provided for substantially reducing and/or canceling third order nonlinearities in circuits, devices, and systems such as amplifiers and mixers. A first coupler is used to split an input signal into two equal-amplitude in-phase components, each component is processed by two nonlinear devices with different nonlinearities, and a final combiner, such as a 180-degree hybrid, recombines the processed signals 180 degrees out of phase and substantially reduces and/or cancels the undesired nonlinear distortion components arising due to nonlinearities in the nonlinear devices.

Claims

1. An apparatus for substantially reducing nonlinear distortion, the apparatus comprising:

a first nonlinear device having an input and an output;

a coupling means having an input in communication with the output of the first nonlinear device and first and second in-phase outputs;

a second nonlinear device having an input in communication with the first in-phase output of the coupling means and an output, wherein the input of the second nonlinear device is independent of the input of the first nonlinear device; and

a subtractor having a first input in communication with the output of the second nonlinear device, a second input in communication with the second in-phase output of the coupling means and an output, wherein the subtractor subtracts the output signal of the second nonlinear device from the second in-phase output of the coupler to generate a final output.

2. The apparatus of claim 1, wherein the first nonlinear device further comprises a first amplifier and the second nonlinear device further comprises a second amplifier.

3. The apparatus of claim 1, wherein the first nonlinear device further comprises a first mixer and the second nonlinear device further comprises a second mixer.

4. The apparatus of claim 1, wherein the first nonlinear device further comprises an amplifier and the second nonlinear device further comprises a diode.

5. The apparatus of claim 1, wherein predetermined nonlinearities an substantially reduced in the final output signal by predetermined selection of a gain of the first nonlinear device, a gain of the second nonlinear device, a nonlinearity of the first nonlinear device, a nonlinearity of the second nonlinear device and selection of the coupling means.

6. The apparatus of claim 1, wherein the first nonlinear device is provided to define a Taylor series expansion describing an output signal, y₁, in terms of an input signal, x₁, as y₁=a₀+a₁x₁+a₂x₁²+a₃x₁³+a₄x₁⁴ . . . , the second nonlinear is provided to define a Taylor series expansion describing an output signal, y₂, in terms of an input signal, x₂, as y₂=b₀+b₁x₂+b₂x₂²+b₃x₂³+b₄x₂⁴ . . . , and the ratio the first in-phase coupled signal to the second in-phase coupled being k.

7. The apparatus of claim 6, wherein signals x₁, x₂, y₁, and y₂ are voltages.

8. The apparatus of claim 6, wherein signals x₁, x₂, y₁, and y₂ are currents.

9. The apparatus of claim 6, wherein third order nonlinearities are substantially reduced by setting, k in the apparatus such that most nearly a₃−

a₃b₁k−

2a₁a₂b₂k²−

a₁³b₃k³=0, and such that a₁−

a₁b₁k does not equal zero.

10. The apparatus of claim 6, wherein second order nonlinearities are substantially reduced by setting, k, in the apparatus such that most nearly a₂−

a₂b₁k−

a₁²b₂k²=0, and such that a₁−

a₁b₁k does not equal zero.

11. A method for substantially reducing nonlinear distortion in an apparatus, the method comprising the steps of:

processing an input signal at a first nonlinear device, the first nonlinear device having a Taylor series expansion describing an output signal, y₁, in terms of an input signal, x₁, as y₁=a₀+a₁x₁+a₂x₁²+a₃x₁³+a₄x₁⁴ . . . ;

splitting, at a coupling means, an output signal of the first nonlinear device into first and second in-phase coupled signals;

processing the first in-phase coupled signal at a second nonlinear device, the second nonlinear device having a Taylor series expansion describing output signal, y₂, in terms of an input signal, x₂, as y₂=b₀+b₁x₂+b₂x₂²+b₃x₂³+b₄x₂⁴ . . . ; and

subtracting an output signal of the second nonlinear device from the second in-phase coupled signal to yield an output difference signal, wherein the output difference signal has substantially reduced nonlinear distortion.

12. The method of claim 11, wherein signals x₁, x₂, y₁, and y₂ are voltages.

13. The method of claim 11, wherein signals x₁, x₂, y₁, and y₂ are currents.

14. The method of claim 11, wherein predetermined nonlinearities are substantially reduced in the final output signal by predetermined selection of a gain of the first nonlinear device, a gain of the second nonlinear device, a nonlinearity of the first nonlinear device, a nonlinearity of the second nonlinear device and selection of the coupling means.

15. The method of claim 11, wherein the ratio of a first in-phase coupled signal to a second in-phase coupled signal, is defined as k and third-order nonlinearities are substantially reduced by setting, k, such that most nearly a₃ −

a₃b₁k−

2a₁a₂b₂k²−

a₁³b₃k³=0, and such that a₁−

a₁b₁k does not equal zero.

16. The method of claim 11, wherein the ratio of a first in-phase coupled signal to a second in-phase coupled signal, is defined as k and second order nonlinearities are substantially reduced by setting, k, such that most nearly a₂−

a₂b₁k−

a₁²b₂k²=0, and such that a₁−

a₁b₁k does not equal zero.

17. An apparatus for substantially reducing nonlinear distortion, the apparatus comprising:

a first mixer device having an input and an output;

a coupling means having an input in communication with the output of the first mixer device and first and second in-phase outputs;

a second mixer device having an input in communication with the first in-phase output of the coupling means and an output, wherein the input of the second mixer device is independent of the input of the first mixer device; and

a subtractor having a first input in communication with the output of the second mixer device, a second input in communication with the second in-phase output of the coupling means and an output, wherein the subtractor subtracts the output signal of the second mixer device from the second in-phase output of the coupler to generate a final output.

18. The apparatus of claim 17, wherein predetermined nonlinearities are substantially reduced in the final output signal by predetermined selection of a gain of the first mixer device, a gain of the second mixer device, a nonlinearity of the first mixer device, a nonlinearity of the second mixer device and selection of the coupling means.

19. The apparatus of claim 17, wherein the first mixer device is provided to define a Taylor series expansion describing an output signal, y₁, in terms of an input signal, x₁, as y₁=a₀+a₁x₁+a₂x₁²+a₃x₁³+a₄x₁⁴ . . . , the second mixer device is provided to define a Taylor series expansion describing an output signal, y₂, in terms of an input signal, x₂, as y₂=b₀+b₁x₂+b₂x₂²+b³x₂³+b₄x₂⁴ . . . , and the ratio the first in-phase coupled signal to the second in-phase coupled being k.

21. The apparatus of claim 17, wherein predetermined nonlinearities are substantially reduced in the final output signal by predetermined selection of a gain of the amplifier device, a gain of the diode device, a nonlinearity of the amplifier device, a nonlinearity of the diode device and selection of the coupling means.

22. The apparatus of claim 17, wherein the amplifier device is provided to define a Taylor series expansion describing an output signal, y₁, in terms of an input signal, x₁, as y₁=a₀+a₁x₁+a₂x₁²+a₃x₁³+a₄x₁⁴ . . . , the diode device is provided to define a Taylor series expansion describing an output signal, y₂, in terms of an input signal, x₂,as y₂=b₀+b₁x₂+b₂x₂²+b₃x₂³+b₄x₂⁴ . . . , and the ratio the first in-phase coupled signal to the second in-phase coupled being k.

20. An apparatus for substantially reducing nonlinear distortion, the apparatus comprising:

an amplifier device having an input and an output;

a coupling means having an input in communication with the output of the amplifier device and first and second in-phase outputs;

a diode device having an input in communication with the first in-phase output of the coupling means and an output, wherein the input of the diode devices is independent of the input of the amplifier device; and

a subtractor having a first input in communication with the output of the diode device, a second input in communication with the second in-phase output of the coupling means and an output, wherein the subtractor subtracts the output signal of the diode device from the second in-phase output of the coupler to generate a final output.

23. An apparatus for substantially reducing nonlinear distortion, the apparatus comprising:

a first nonlinear device having an input and an output;

a coupling means having an input in communication with the output of the first nonlinear device and first and second in-phase outputs;

a second nonlinear device having an input in communication with the first in-phase output of the coupling means and an ouput; and

a subtractor having a first input in communication with the output of the second nonlinear device, a second input in communication with the second in-phase output of the coupling means and an output,

wherein the subtractor subtracts the output signal of the second nonlinear device from the second in-phase output of the coupler to generate a final output, the first nonlinear device is provided to define a Taylor series expansion describing an output signal, y₁, in terms of an input signal, x₁,as y₁=a₀+a₁x₁+a₂x₁²+a₃x₁³+a₄x₁⁴ . . . , the second nonlinear device is provided to define a Taylor series expansion describing an output signal, y₂, in terms of an input signal, x₂,as y₂=b₀+b₁x₂+b₂x₂²+b₃x₂³+b₄x₂⁴ and the ratio the first in-phase coupled signal to the second in-phase coupled being k.

24. The apparatus of claim 23, wherein signals x₁, x₂, y₁, and y₂ are voltages.

25. The apparatus of claim 23, wherein signals x₁, x₂, y₁, and y₂ are currents.

26. The apparatus of claim 23, wherein third order nonlinearities are substantially reduced by setting, k, in the apparatus such that most nearly a₃−

a₃b₁k−

2a₁a₂b₂k²−

a₁³b₃k³=0, and such that a₁−

a₁b₁k does not equal zero.

27. The apparatus of claim 23, wherein second order nonlinearities are substantially reduced by setting, k, in the apparatus such that most nearly a₂−

a₂b₁k−

a₁²b₂k²=0, and such that a₁−

a₁b₁k does not equal zero.