Methods and apparatus for substantially reducing third order intermodulation distortion and other nonlinear distortions

• US 20040169559A1
• Filed: 03/05/2004
• Published: 09/02/2004
• Est. Priority Date: 03/19/2002
• Status: Active Grant

• 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
• Granted Patent: US 6,906,585 B2
• Time in Patent Office: Days
• 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:

an input coupling means having an input and first and second outputs, the input coupling means capable of splitting an input signal into first and second coupled signals that are in-phase with respect to each other;

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

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

a subtractor having a first input in communication with the output of the first nonlinear device, a second input in communication with the output of the second nonlinear device and an output, wherein the subtractor is capable of subtracting an output signal of the second nonlinear device from an output signal of the first nonlinear device to generate a final output signal.

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 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 input coupling means.

6. The apparatus of claim 1, wherein the first nonlinear device defines a gain as G₁ dB, the second nonlinear device defines a gain as G₂ dB, the first nonlinear device defines a third order output intercept point as OIP3₁ dBm and the second nonlinear device defines a third order output intercept point as OIP3₂ dBm, and K=10 log₁₀(p₂/p₁), where p₁ is the input signal power level of the first nonlinear device and p₂ is the input signal power level of the second nonlinear device, such that the first and second nonlinear devices and the input coupling means are provided such that most nearly 2(OIP3₁−

OIP3₂)=3(G₁−

G₂−

K), where G₁ is not equal G₂+K and such that the first and second nonlinear devices have substantially equal time delay and phase to substantially reduce third order nonlinearity.

7. The apparatus of claim 1, wherein the first nonlinear device is provided such that it has a Taylor series expansion describing the output signal of the first nonlinear device, y₁, in terms of an input signal of the first nonlinear device, x₁, as y₁=a₀+a₁x₁+a₂x₁²+a₃x₁³+a₄x₁⁴ . . . , the second nonlinear device is provided such that it has a Taylor series expansion describing the output signal of the second nonlinear device, y₂ in terms of an input signal of the second nonlinear device, X₂, as y₂=b₀+b₁x₂+b₂x₂²+b₃x₂³+b₂x₂⁴ . . . , the ratio, k, is provided such that k=x₂/x₁, where k is set by the input coupling means provided, such that nonlinearities of order n are substantially reduced and/or canceled by setting most nearly k=(a_n/b_n)^1/n.

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

9. The apparatus of claim 7, wherein signals x₁, x₂, y₁, and y₂ are currents.

10. A method for substantially reducing third order distortion in an apparatus, the method comprising the steps of:

splitting an input signal into first and second in-phase coupled signals, the ratio of a second in-phase coupled signal power, p₂, to a first coupled signal power, p₁, is defined as K=10 log₁₀(p₂/p₁);

processing the first in-phase coupled signal at a first nonlinear device and the second in-phase coupled signal at a second nonlinear device, the first nonlinear device has a gain defined as, G₁ dB, and a third order output intercept point defined as, OIP3₁ dBm, the second nonlinear device has a gain defined as, G₂ dB, and a third order output intercept point defined as, OIP3₂ dBm, such that the relationship between the first and second nonlinear devices and the input coupling means is defined as, most nearly 2(OIP3₁−

OIP3₂)=3(G₁−

G₂−

K), where G₁ is not equal to G₂+K and the first and second nonlinear devices have substantially equal time delay and phase; and

subtracting an output signal of the second nonlinear device from an output signal of the first nonlinear device to yield a final output signal that substantially reduces third order nonlinearities.

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

splitting an input signal into first and second in-phase coupled signals, wherein the ratio of the second in-phase coupled signal, x₂, to the first in-phase coupled signal, x₁, is defined as k=x₂/x₁;

processing the first in-phase coupled signal at a first nonlinear device and the second in-phase coupled signal at a second nonlinear device, the first nonlinear device has 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 has a Taylor series expansion describing an output signal y₂, in terms of an input signal, x₂, as y₂=b₀+b₁x₂+b₂x₂²+b₃x₂³+b₄x₂⁴ . . . , such that the first and second nonlinear devices and the input coupling means are defined as most nearly k=(a_n/b_n)^1/n; and

subtracting an output signal of the second nonlinear device from an output signal of the first nonlinear device to yield a final output signal that substantially reduces nonlinear distortion of order n.

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.