METHOD AND APPARATUS FOR LOW INTERMODULATION DISTORTION AMPLIFICATION IN SELECTED BANDS

• US 20040232983A1
• Filed: 05/21/2003
• Published: 11/25/2004
• Est. Priority Date: 05/21/2003
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Cheung, Peter Y., Liu, Kuang Yung, Vollbrecht, Jennifer Y., Wah, Lauriston Chin, Crampton, David L.
• Granted Patent: US 6,922,103 B2
• Time in Patent Office: Days
• US Class Current: 330/149
• CPC Class Codes: H03H 17/0213 Frequency domain filters using Fourier transforms
• CPC Class Codes: H03H 17/0261 Non linear filters

Abstract

A method and apparatus for reducing intermodulation distortion is disclosed. In one embodiment, the method comprises the steps of accepting a sampled input signal V(t) wherein the input signal V(t) comprises a plurality of peaks; determining n peaks V_p1,V_p2, . . . ,V_pn of the sampled input signal V(t) exceeding a clip value V_clip at times t₁,t₂, . . . ,t_n; and modifying the sampled input signal V(t) by weighting the n peaks V_p1,V_p2, . . . ,V_pn exceeding the clip value V_clip of the sampled input signal V(t) by a function b(t) wherein b(t) is either a hard limiting function or b(t)=ƒ(a₁,a₂, . . . a_n;t-t_p1,t-t_p2, . . . t-t_pn), wherein a₁,a₂, . . . a_n are weight values corresponding to the n peaks V_p1,V_p2, . . . ,V_pn, and ƒ(t-t_p1,t-t_p2, . . . t-t_pn) is a smooth shaping function. Intermodulation performance is then selectively improved in selected sub-bands by notch filtering prior to application to the non-linearity.

Claims

1. A method of reducing intermodulation distortion, comprising the steps of:

(a) accepting a sampled input signal V(t) wherein the input signal V(t) comprises a plurality of peaks;

(b) determining n peaks V_p1,V_p2, . . . ,V_pn of the sampled input signal V(t) exceeding a clip value V_clip at times t₁,t₂, . . . t_n; and

(c) modifying the sampled input signal V(t); and

(d) notch filtering the modified sampled input signal V(t) to remove intermodulation components of the modified sampled input signal V(t).

2. The method of claim 1, wherein the step of modifying the sampled input signal V(t) comprises the step of weighting then peaks V_p1,V_p2, . . . ,V_pn exceeding the clip value V_clip of the sampled input signal V(t) by b(t)=ƒ

(a₁, a₂, . . . a_n;

t-t_p1,t-t_p2, . . . t-t_pn), wherein a₁, a₂, . . . a_n are weight values corresponding to the n peaks V_p1,V_p2, . . . ,V_pn, and ƒ

(t-t_p1,t-t_p2, . . . t-t_pn) is a smooth shaping function.

3. The method of claim 2, wherein the function b(t) comprises a Gaussian density function.

4. The method of claim 3, wherein the function b(t) comprises

5. The method of claim 2, wherein

6. The method of claim 1, wherein the function b(t) comprises a hard limiting function.

7. The method of claim 1, wherein the step of notch filtering the modified sampled input signal V(t) to remove intermodulation components of the modified sampled input signal V(t) comprises the steps of:

(d1) transforming the modified sampled input signal V(t) into a frequency domain representation having a plurality of intermodulation components;

(d2) removing the intermodulation components; and

(d3) transforming the frequency domain representation without the intermodulation components to a time domain.

8. The method of claim 1, wherein the step of notch filtering the modified sampled input signal V(t) to remove intermodulation components of the modified sampled input signal V(t) comprises the steps of:

(d1) fast Fourier transforming the modified sampled input signal V(t) to produce a first processed signal;

(d2) generating a second processed signal by removing the intermodulation components of the first processed signal; and

(d3) generating the notch filtered modified sampled input signal V(t) by inverse fast Fourier transforming the second processed signal.

9. The method of claim 1, wherein:

the sampled input signal V(t) comprises a plurality of carriers, collectively having carrier components in a frequency domain; and

wherein the method further comprises the step of notch filtering the modified sampled input signal V(t) to remove the non-carrier components.

10. The method of claim 9, wherein the step of notch filtering the modified sampled input signal V(t) to remove the non-carrier components comprises the steps of:

(d1) transforming the modified sampled input signal V(t) into a frequency domain representation having the carrier components and the non-carrier components;

(d2) removing all of the non-carrier components; and

(d3) transforming the frequency domain representation carrier components to a time domain.

11. The method claim 10, wherein the function b(t) comprises a hard limiting function and the method further comprises the step of:

iteratively repeating steps (c)-(d3).

12. The method of claim 9, wherein the step of notch filtering the modified sampled input signal V(t) to remove the non-carrier components comprises the steps of:

fast Fourier transforming the modified sampled input signal V(t) to produce a first processed signal;

generating a second processed signal by removing all of the non-carrier components of the first processed signal; and

generating the notch filtered modified sampled input signal V(t) by inverse fast Fourier transforming the second processed signal.

13. An apparatus for reducing intermodulation distortion, comprising:

a gain control module, for accepting a sampled input signal V(t) wherein the input signal V(t) comprises a plurality of peaks, for determining n peaks V_p1,V_p2, . . . ,V_pn of the sampled input signal V(t) exceeding a clip value V_clip at times t₁,t₂, . . . t_n and for determining a weight value

$a_n=1-\frac{V_{\mathrm{clip}}}{V_{p_n}};<br><br>$

a signal conditioning module, for modifying the sampled input signal; and

a notch filter, for filtering the modified sampled input signal V(t) to remove intermodulation components of the modified sampled input signal V(t).

14. The apparatus of claim 13, wherein the signal conditioning module weights the n peaks V_p1,V_p2, . . . ,V_pn exceeding the clip value V_clip of the sampled input signal V(t) by a function b(t)=ƒ

(a₁, a₂, . . . a_n;

t-t_p1,t-t_p2, . . . t-t_pn), wherein a₁, a₂, . . . a_n are weight values corresponding to the n peaks V_p1,V_p2, . . . ,V_pn, and ƒ

(t-t_p1,t-t_p2, . . . t-t_pn) is a smooth shaping function.

15. The apparatus of claim 14, wherein the function b(t) comprises a Gaussian density function.

16. The apparatus of claim 15, wherein the function b(t) comprises

17. The apparatus of claim 13, wherein the notch filtered comprises:

a fast Fourier transform module;

a frequency domain component editor module;

an inverse fast Fourier transform module.

18. The apparatus of claim 17, wherein the input signal V(t) comprises a plurality of carriers.

19. The apparatus of claim 13, wherein the signal conditioning module comprises a hard limiter.

21. The apparatus of claim 18, wherein the means for modifying the input signal V(t) weights the n peaks V_p1,V_p2, . . . ,V_pn exceeding the clip value V_clip of the input signal V(t) by a function b(t)=ƒ

(a₁, a₂, . . . a_n;

t-t_p1,t-t_p2, . . . t-t_pn), wherein a₁, a₂, . . . a_n are weight values corresponding to the n peaks V_p1,V_p2, . . . ,V_pn, and ƒ

(t-t_p1,t-t_p2, . . . t-t_pn) is a smooth shaping function.

22. The apparatus of claim 21, wherein the function b(t) comprises a Gaussian density function.

23. The apparatus of claim 22, wherein the function b(t) comprises

24. The apparatus of claim 21, wherein

26. The apparatus of claim 24, wherein the means for notch filtering the modified input signal V(t) to remove intermodulation components of the modified input signal V(t) comprises:

(d) means for fast Fourier transforming the modified input signal V(t) to produce a first processed signal;

(e) means for generating a second processed signal by removing the intermodulation components of the first processed signal; and

(f) means for generating the notch filtered modified input signal V(t) by inverse fast Fourier transforming the second processed signal.

20. An apparatus for reducing intermodulation distortion, comprising the steps of:

(a) means for accepting an input signal V(t) wherein the input signal V(t) comprises a plurality of peaks;

(b) means for determining n peaks V_p1,V_p2, . . . ,V_pn of the input signal V(t) exceeding a clip value V_clip at times t₁,t₂, . . . t_n; and

(c) means for modifying the input signal V(t); and

(d) means for notch filtering the modified input signal V(t) to remove intermodulation components of the modified input signal V(t).

25. The apparatus of claim 20, wherein the means for notch filtering the modified input signal V(t) to remove intermodulation components of the modified input signal V(t) comprises:

(d) means for transforming the modified input signal V(t) into a frequency domain representation having a plurality of intermodulation components;

(e) means for removing the intermodulation components; and

(f) means for transforming the frequency domain representation without the intermodulation components to a time domain.

27. The apparatus of claim 20, wherein:

the input signal V(t) comprises a plurality of carriers, collectively having carrier components in a frequency domain; and

wherein the apparatus further comprises means for notch filtering the modified input signal V(t) to remove the non-carrier components.

28. The apparatus of claim 27, wherein the means for notch filtering the modified input signal V(t) to remove the non-carrier components comprises:

(d) means for transforming the modified input signal V(t) into a frequency domain representation having the carrier components and the non-carrier components;

(e) means for removing all of the non-carrier components; and

(f) means for transforming the frequency domain representation carrier components to a time domain.

29. The apparatus of claim 27, wherein the means for notch filtering the modified input signal V(t) to remove the non-carrier components comprises:

means for fast Fourier transforming the modified input signal V(t) to produce a first processed signal;

means for generating a second processed signal by removing all of the non-carrier components of the first processed signal; and

means for generating the notch filtered modified input signal V(t) by inverse fast Fourier transforming the second processed signal.

30. The apparatus of claim 20, wherein the means for modifying the input signal V(t) comprises means for hard limiting the input signal V(t).