System of and method for compensating a baseband signal to reduce third order modulation distortion

• US 6,731,693 B1
• Filed: 02/29/2000
• Issued: 05/04/2004
• Est. Priority Date: 02/29/2000
• Status: Expired due to Term

• Current Assignee: MediaTek, Inc.
• Original Assignee: Skyworks Solutions Incorporated
• Inventors: Damgaard, Morten
• Primary Examiner(s): Tran, Khai
• Assistant Examiner(s): TRAN, KHANH C
• Application Number:
  US09/515,538
• Time in Patent Office: 1,526 Days
• Field of Search: 375/296, 375/297, 375/302, 375/298, 375/373, 375/376, 455/114, 455/115, 455/125, 455/126, 455/116, 455/63, 455/67.1, 455/67.3, 330/149, 331/25, 331/14, 331/16, 331/17, 332/107, 332/123, 332/124, 332/127, 332/128, 332/159, 332/160, 332/162, 332/161, 332/176
• US Class Current: 375/296
• CPC Class Codes: H04L 27/206 using a pair of orthogonal carriers, e.g. quadrature carriers
• CPC Class Codes: H04L 27/367 using predistortion

Abstract

A system for and method of overcoming third order modulation distortion in which a baseband signal is predistorted using one or more parameters configured to reduce or eliminate the third order modulation distortion.

Claims

1. A system for predistorting a baseband signal to reduce or eliminate third order modulation distortion products comprising:

a predistortion circuit for predistorting a baseband signal to reduce or eliminate third order modulation distortion products, the predistortion circuit responsive to one or more predistortion parameters;

a quadrature modulator for modulating the predistorted baseband signal; and

a distortion detector for measuring third order modulation distortion products, and, responsive thereto, determining the one or more predistortion parameters.

2. The system of claim 1 wherein the predistortion circuit includes one or more lookup tables for determining the components I′

and Q′

of the predistorted baseband signal.

3. The system of claim 1 wherein the one or more predistortion parameters are stored in a memory in the predistortion circuit.

4. The system of claim 1 wherein the distortion detector measures third order modulation distortion products at the output of the modulator.

5. The system of claim 1 further comprising a translational loop for upconverting the modulator output to RF frequencies.

6. The system of claim 5 wherein the distortion detector measures distortion derived from third order modulation distortion products at the output of the translational loop.

7. The system of claim 1 wherein the one or more predistortion parameters θ

₃₊, C₃₊, θ

₃₋

, and C₃₋

in the following equations (in which I and Q are the components of the baseband signal);

8. The system of claim 7 wherein the predistortion parameters θ

₃₊, C₃₊, and θ

₃₋

and C₃₋

bear the following relationships to A₃₊, Δ

₃₊, A₃₋

, and Δ

₃₋

;

9. A method for predistorting a baseband signal to reduce or eliminate third order modulation distortion comprising the steps of:

measuring third order modulation distortion products in a modulated baseband signal;

determining one or more parameters configured to reduce or eliminate third order modulation distortion in the modulated baseband signal;

predistorting the baseband signal responsive to the one or more parameters;

quadrature modulating the baseband signal to generate the modulated baseband signal; and

deriving a transmission signal from the modulated baseband signal.

10. The method of claim 9 wherein the one or more parameters comprise θ

₃₊, C₃₊, θ

₃₋

, and C₃₋

, and the predistorting step comprises predistorting I and Q, the components of the baseband signal in accordance with the following equations;

11. The method of claim 9 wherein the deriving step comprises upconverting the modulated baseband signal.

12. The method of claim 9 in which the predistorting step includes generating the components I′

and Q′

of the predistorted baseband signal using one or more table lookups.

13. A method of deriving one or more predistortion parameters comprising the steps of:

detecting distortion which is or is derived from third order modulation distortion;

adjusting one or parameters responsive thereto if the detected distortion is not below a predetermined threshold;

predistorting a baseband signal using the one or parameters;

performing the foregoing steps one or more times until the detected distortion is below the predetermined threshold; and

storing the one or more parameters.

14. The method of claim 13 wherein the one or more parameters comprise θ

₃₊, C₃₊, θ

₃₋

, and C₃₋

, and the predistorting step comprises predistorting I and Q, the components of the baseband signal, in accordance with the following equations;

15. The method of claim 14 wherein the first, second, and third steps are repeatedly performed until the parameters θ

₃₊, C₃₊, θ

₃₋

, and C₃₋

, bear the following relationship to A₃₊, Δ

₃₊, A₃₋

, and Δ

₃₋

;