Linearizing LINC amplifiers using pre-distortion

• US 20040027198A1
• Filed: 08/05/2003
• Published: 02/12/2004
• Est. Priority Date: 08/09/2002
• Status: Active Grant

• Current Assignee: CommScope Technologies, LLC (CommScope Holding Company, Inc.)
• Original Assignee: Andrew Corporation (CommScope Holding Company, Inc.)
• Inventors: Chandrasekaran, Rajiv, Dodd, Andrew
• Granted Patent: US 6,930,547 B2
• Time in Patent Office: Days
• US Class Current: 330/149
• CPC Class Codes: H03F 1/0294 using vector summing of two or more constant amplitude phase-modulated signals
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence

Abstract

An input signal having amplitude information is pre-distorted and converted into two pre-distorted signals without amplitude information. The two pre-distorted signals are separately amplified and then recombined to generate a linearized amplified output signal having amplitude information. The pre-distortion and conversion may be implemented using a pre-distorter and a LINC modulator. Alternatively, the pre-distortion and conversion may be implemented in circuitry that combines the functions of a pre-distorter and a LINC modulator. The amplified, pre-distorted signals are preferably combined using circuitry that provides at least some impedance matching, such as a transformer or a transmission line tee with transmission line stubs.

Claims

1. A method for generating a linearized amplified output signal from an input signal having amplitude information, the method comprising:

converting the input signal into two pre-distorted signals without amplitude information;

separately amplifying the two pre-distorted signals; and

combining the two amplified, pre-distorted signals to generate the linearized amplified output signal.

2. The invention of claim 1, wherein:

the input signal is an RF signal; and

the linearized amplified output signal is an RF signal having amplitude information.

3. The invention of claim 1, wherein converting the input signal comprises:

pre-distorting the input signal to generate a pre-distorted input signal; and

converting the pre-distorted input signal into the two pre-distorted signals without amplitude information.

4. The invention of claim 3, wherein pre-distorting the input signal comprises pre-distorting both amplitude and phase of the input signal.

5. The invention of claim 1, wherein converting the input signal comprises:

generating a phase pre-distortion term from the input signal;

generating an amplitude pre-distortion term from the input signal;

detecting phase of the input signal;

combining the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a first manner and modulating at a carrier frequency to generate a first pre-distorted signal without amplitude information; and

combining the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a second manner and modulating at the carrier frequency to generate a second pre-distorted signal without amplitude information.

6. The invention of claim 5, wherein generating the phase and amplitude pre-distortion terms comprise:

detecting amplitude of the input signal;

retrieving the phase pre-distortion term from a first look-up table based on the detected amplitude; and

retrieving the amplitude pre-distortion term from a second look-up table based on the detected amplitude.

7. The invention of claim 5, wherein:

in the first manner, the amplitude pre-distortion term is subtracted from the sum of the phase pre-distortion term and the phase; and

in the second manner, the amplitude pre-distortion term is added to the sum of the phase pre-distortion term and the phase.

8. The invention of claim 1, wherein combining the two amplified, pre-distorted signals is implemented using a transformer.

9. The invention of claim 1, wherein combining the two amplified, pre-distorted signals is implemented using a transmission line tee with transmission stubs for impedance matching.

10. The invention of claim 9, wherein the transmission stubs comprise shunt reactances place an electrical equivalent of one-quarter wavelength away from the transmission line tee.

11. An amplifier circuit adapted to generate a linearized amplified output signal from an input signal having amplitude information, the amplifier circuit comprising:

means for converting the input signal into two pre-distorted signals without amplitude information;

means for separately amplifying the two pre-distorted signals; and

means for combining the two amplified, pre-distorted signals to generate the linearized amplified output signal.

12. An amplifier circuit adapted to generate a linearized amplified output signal from an input signal having amplitude information, the amplifier circuit comprising:

circuitry adapted to convert the input signal into two pre-distorted signals without amplitude information;

two amplifiers adapted to separately amplify the two pre-distorted signals; and

a combiner adapted to combine the two amplified, pre-distorted signals to generate the linearized amplified output signal.

13. The invention of claim 12, wherein:

the input signal is an RF signal; and

the linearized amplified output signal is an RF signal having amplitude information.

14. The invention of claim 12, wherein the circuitry adapted to convert the input signal comprises:

a pre-distorter adapted to pre-distort the input signal to generate a pre-distorted input signal; and

a LINC modulator adapted to convert the pre-distorted input signal into the two pre-distorted signals without amplitude information.

15. The invention of claim 14, wherein the pre-distorter is adapted to pre-distort both amplitude and phase of the input signal.

16. The invention of claim 12, wherein the circuitry adapted to convert the input signal comprises:

circuitry adapted to generate a phase pre-distortion term from the input signal;

circuitry adapted to generate an amplitude pre-distortion term from the input signal;

a phase detector adapted to detect phase of the input signal;

circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a first manner and modulating at a carrier frequency to generate a first pre-distorted signal without amplitude information; and

circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in a second manner and modulating at the carrier frequency to generate a second pre-distorted signal without amplitude information.

17. The invention of claim 16, wherein the circuitry adapted to generate the phase and amplitude pre-distortion terms comprises:

an envelope detector adapted to detect amplitude of the input signal;

a first look-up table adapted to provide the phase pre-distortion term based on the detected amplitude; and

a second look-up table adapted to provide the amplitude pre-distortion term based on the detected amplitude.

18. The invention of claim 16, wherein:

the circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in the first manner is adapted to generate a signal corresponding to the amplitude pre-distortion term subtracted from the sum of the phase pre-distortion term and the phase ; and

the circuitry adapted to combine the phase pre-distortion term, the amplitude pre-distortion term, and the phase in the second manner is adapted to generate a signal corresponding to the amplitude pre-distortion term added to the sum of the phase pre-distortion term and the phase.

19. The invention of claim 18, wherein the circuitry adapted to generate the first and second pre-distorted signals without amplitude information comprises:

a subtraction node adapted to subtract the amplitude pre-distortion term from the phase pre-distortion term;

a first addition node adapted to add the amplitude pre-distortion term to the phase pre-distortion term;

a second addition node adapted to add the phase to the output from the subtraction node;

a first modulator adapted to modulate the output from the second addition node at the carrier frequency to generate the first pre-distorted signal without amplitude information;

a third addition node adapted to add the phase to the output from the first addition node; and

a second modulator adapted to modulate the output from the third addition node at the carrier frequency to generate the second pre-distorted signal without amplitude information.

20. The invention of claim 12, wherein the combiner comprises a transformer.

21. The invention of claim 12, wherein combiner comprises a transmission line tee with transmission stubs for impedance matching.

22. The invention of claim 21, wherein the transmission stubs comprise shunt reactances place an electrical equivalent of one-quarter wavelength away from the transmission line tee.