Feedforward amplifier linearization adapting off modulation

• US 6,525,603 B1
• Filed: 01/05/2001
• Issued: 02/25/2003
• Est. Priority Date: 01/05/2001
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: REMEC, Inc.
• Inventors: Morgan, Denny Edward
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/756,038
• Time in Patent Office: 781 Days
• Field of Search: 330/52, 330/149, 330/151
• US Class Current: 330/52
• CPC Class Codes: H03F 1/3235 using a pilot signal

Abstract

A feedforward amplifier is linearized by adapting off the detection of an applied modulation source. The feedforward amplifier has two loops: a first loop and a second loop. Modulators in the two loops are adjusted by controllers that adapt in response to detection of the modulation source injected into the first loop.

Claims

1. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein the input signal is modulated to create a single additional sideband with a carrier signal maintained.

2. A method as defined in claim 1, wherein the single additional sideband is about 30 dB below the carrier single amplitude.

3. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein a single RF mixer is used to downconvert the feedforward amplifier output to a baseband signal.

4. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein an I/Q mixer is used to downconvert the feedforward amplifier output to a baseband signal.

5. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein a plurality of synchronous detectors are used to detect the presence of the modulation of the input signal in the output of the feedforward amplifier.

6. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein detecting the presence of the modulation source signal is performed using an I/Q mixer.

7. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein detecting the presence of the modulation source signal is performed using a plurality of synchronous detectors.

8. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein the modulation source signal frequency is selected to result in sidebands that fall within the spectral nulls of the signal mixed with itself.

9. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein adaptively modulating and amplifying of the error signal is in response to scalar parameters derived from vector outputs of detectors sensing the presence of the modulating source in the power amplifier output.

10. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein adaptively modulating and amplifying of the error signal is performed in response to a matrix sensitivity derived from vector error versus phase and amplitude outputs of detectors sensing the presence of the modulating source in the main amplifier output.

11. A method as defined in claim 10, wherein the matrix sensitivity derived from the vector error versus phase and amplitude outputs of the detectors is fixed.

12. A method as defined in claim 10, wherein the matrix sensitivity derived from the vector error versus phase and amplitude adjusters is stored in a lookup table.

13. A method of reducing distortion in a feedforward amplifier output signal, the method comprising:

receiving an input signal;

modulating the input signal with a modulation source signal;

delivering the modulated input signal to a main amplifier to produce an output;

extracting a sample of the output of the main amplifier;

subtracting a sample of the input signal from the extracted sample of the output of the main amplifier thereby producing an error signal;

detecting the presence of the modulation source signal in the output of the feedforward amplifier; and

adaptively modulating and amplifying the error signal, and combining the modulated and amplified error signal with the main amplifier output so as to minimize the presence of the modulation source signal in the output of the feedforward amplifier;

wherein adaptation is stopped, or retarded, when the input signal level decreases below a threshold.

14. A feedforward amplifier comprising:

a first loop modulator configured to accept an input signal and output a modulated primary signal in response to a modulation source and a first loop controller;

a main amplifier configured to accept the modulated primary signal and output a power amplifier signal;

a first loop directional coupler configured to extract a sample of the power amplifier signal;

a power combiner configured to accept, and combine, the input signal and the extracted sample of the power amplifier signal and to output a distortion signal;

a second loop modulator configured to accept the distortion signal, adjust the distortion signal in response to a second loop controller, and to output a modulated distortion signal;

an error amplifier configured to accept, and amplify, the modulated distortion signal and output a correction signal;

a power directional coupler configured to accept the correction signal and the power amplifier signal and output a power signal;

a power signal sense directional coupler configured to extract a sample of the power signal;

a detection circuit configured to accept the sample of the power signal and detect the amplitude of the modulation signal present in the power signal;

a sense signal directional coupler configured to extract a sample of the input signal; and

an automatic gain control circuit configured to accept the sample of the sense signal and to output a voltage level used to adjust gains in the detector circuit and monitored by the first loop controller and the second loop controller.

15. A feedforward amplifier as defined in claim 14, wherein the modulation source has a frequency between about 100 Hz and about 100 kHz.

16. A feedforward amplifier as defined in claim 14, wherein the modulation source has a frequency that occurs at about a spectral null of the input signal mixed with itself.

17. A feedforward amplifier as defined in claim 14, wherein the first loop modulator comprises a variable attenuator.

18. A feedforward amplifier as defined in claim 14, wherein the first loop modulator comprises is a variable gain amplifier.

19. A feedforward amplifier as defined in claim 14, wherein the first loop modulator comprises a phase shifter.

20. A feedforward amplifier as defined in claim 14, wherein the second loop modulator is a vector I/Q modulator.

21. A feedforward amplifier as defined in claim 14, wherein the second loop modulator comprises a variable gain amplifier.

22. A feedforward amplifier as defined in claim 14, wherein the second loop modulator comprises a phase shifter.

23. A feedforward amplifier as defined in claim 14, wherein the second loop modulator is a vector I/Q modulator.

24. A feedforward amplifier as defined in claim 14, wherein the detection circuit is a synchronous detector.

25. A feedforward amplifier as defined in claim 14, wherein the modulated primary signal is amplitude modulated.

26. A feedforward amplifier as defined in claim 14, wherein the modulated primary signal is phase modulated.

27. A feedforward amplifier as defined in claim 14, wherein the modulated primary signal is single sideband modulated.