Method and apparatus for reduction of distortion in a feed forward amplifier

• US 6,700,441 B1
• Filed: 09/17/2002
• Issued: 03/02/2004
• Est. Priority Date: 09/17/2002
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Zhang, Wentian, Irons, Bryan Todd, Van Horn, Mark Ian
• Primary Examiner(s): Nguyen, Khanh Van
• Application Number:
  US10/245,062
• Time in Patent Office: 532 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 feed forward amplifier performs a carrier cancellation tuning process separate from an IM reduction tuning process, wherein the carrier cancellation tuning process is performed without reference modulations that are utilized to modulate a feed forward amplifier input signal during the IM reduction tuning process. By decoupling the reference modulations during the carrier cancellation process, the feed forward amplifier is able to eliminate the instantaneous carrier cancellation degradation that would otherwise be caused by the reference modulations.

Claims

1. A method for reducing distortion in a feed forward amplifier comprising steps of:

modulating an input signal of the feed forward amplifier with a reference modulation based on a reference signal to produce a reference signal modulated input signal;

amplifying the reference signal modulated input signal to produce an amplified signal;

determining an error signal based on the input signal and the amplified signal;

amplifying the error signal to produce an amplified error signal;

determining a corrected output signal based on the amplified signal and the amplified error signal;

detecting a residual modulation in the corrected output signal, wherein the detected residual modulation corresponds to the reference modulation applied to the input signal;

correlating the detected residual modulation and the reference signal to determine a correlation;

generating at least one control signal based on the correlation, wherein the at least one control signal is capable of controlling error signal adjustments;

holding the control signal constant;

decoupling the reference modulation from the input signal; and

optimizing carrier cancellation with the reference modulation decoupled.

2. The method of claim 1, wherein the step of detecting a residual modulation comprises a step of detecting a residual amplitude modulation.

3. The method of claim 1, wherein the step of amplifying the error signal comprises steps of:

adjusting the error signal to produce an adjusted error signal; and

amplifying the adjusted error signal to produce an amplified error signal.

4. The method of claim 1, wherein the step of modulating an input signal comprises a step of modulating an amplitude of an input signal of the feed forward amplifier with a reference amplitude modulation based on a first reference signal and modulating a phase of the input signal with a reference phase modulation based on a second reference signal to produce a reference signal modulated input signal, wherein the step of correlating comprises a step of correlating the detected residual modulation with the first reference signal to produce an amplitude correlation and correlating the detected residual modulation with the second reference signal to product a phase correlation, wherein the step of generating comprises a step of generating an amplitude control signal based on the amplitude correlation and generating a phase control signal based on the phase correlation, and wherein the amplitude control signal is capable of controlling an adjustment of an amplitude of the error signal and the phase control signal is capable of controlling an adjustment of a phase of the error signal.

5. The method of claim 4, wherein the reference amplitude modulation and the reference phase modulation each comprises a same pilot tone.

6. The method of claim 1, wherein the step of modulating an input signal comprises a step of modulating an in-phase component of an input signal of the feed forward amplifier with a fist reference modulation based on a first reference signal and modulating a quadrature component of the input signal with a second reference modulation based on a second reference signal to produce a reference signal modulated input signal, wherein the step of correlating comprises a step of correlating the detected residual modulation with the first reference signal to produce an in-phase component correlation and correlating the detected residual modulation with the second reference signal to produce a quadrature component correlation, wherein the step of generating comprises a step of generating an in-phase component control signal based on the in-phase component correlation and generating a quadrature control signal based on the quadrature correlation, and wherein the in-phase component control signal is capable of controlling an adjustment of an in-phase component of the error signal and the quadrature component control signal is capable of controlling an adjustment of a quadrature component of the error signal.

7. The method of claim 6, wherein the first reference modulation and the second reference modulation each comprises a same pilot tone.

8. A method for reducing distortion in a feed forward amplifier comprising steps of:

modulating a first component of an input signal of the feed forward amplifier with a first reference modulation based on a first reference signal to produce a first modulated signal;

amplifying the first modulated signal to produce a first amplified signal;

determining a first error signal based on the input signal and the first amplified signal;

amplifying the first error signal to produce a first amplified error signal;

determining a first connected output signal based on the first amplified signal and the first amplified error signal;

detecting a first residual modulation in the first corrected output signal, wherein the detected first residual modulation corresponds to the first reference modulation;

correlating the detected first residual modulation and the first reference signal to determine a first correlation;

generating a first control signal based on the first correlation;

adjusting a first component of the error signal based on the first control signal;

holding the first control signal constant;

decoupling the first reference modulation from the input signal;

modulating a second component of the input signal of the feed forward amplifier with a second reference modulation based on a second reference signal to produce a second modulated signal;

amplifying the second modulated signal to produce a second amplified signal;

determining a second error signal based on the input signal and the second amplified signal;

amplifying the second error signal to produce a second amplified error signal;

determining a second corrected output signal based on the second amplified signal and the second amplified error signal;

detecting a second residual modulation in the second corrected output signal, wherein the detected second residual modulation corresponds to the second reference modulation;

correlating the detected second residual modulation and the second reference signal to determine a second correlation;

generating second control signal based on the second correlation;

adjusting a second component of the error signal based on the second control signal;

holding the second control signal constant;

decoupling the second reference modulation from the input signal; and

tuning a carrier cancellation performance of the feed forward amplifier with the first reference modulation and the second reference modulation decoupled.

9. The method of claim 8, wherein the first component of the input signal comprises an amplitude of the input signal, the first component of the error signal comprises an amplitude of the error signal, the second component of the input signal comprises a phase of the input signal, and the second component of the error signal comprises a phase of the error signal.

10. The method of claim 8, wherein the first component of the input signal comprise a phase of the input signal, the first component of the error signal comprises a phase of the error signal, the second component of the input signal comprises an amplitude of the input signal, and the second component of the error signal comprises an amplitude of the error signal.

11. The method of claim 8, wherein the first component to the input signal comprises an in-phase component of the input signal, the first component of the error signal comprises an in-phase of the error signal, the second component of the input signal comprises a quadrature of the input signal, and the second component of the error signal comprises a quadrature of the error signal.

12. The method of claim 8, wherein the first component of the input signal comprises a quadrature component of the input signal, the first component of the error signal comprises a quadrature of the error signal, the second component of the input signal comprises an in-phase of the input signal, and the second component of the error signal comprises an in-phase of the error signal.

13. The method of claim 8, wherein the first reference signal and the second reference signal each comprises a same pilot tone.

14. A feed forward amplifier comprising:

a main signal path that receives an input signal, modulates the input signal with a reference modulation based on a reference signal to produce a modulated input signal, amplifies the modulated input signal to produce an amplified signal, and combines the amplified signal with an amplified error signal to produce a corrected output signal;

a feed forward correction circuit coupled to the main signal path that receives at least a portion of the input signal, receives a portion of the amplified signal, determines an error signal based on the at least a portion of the input signal and the portion of the amplified signal, produces the amplified error signal based on the error signal, and conveys the amplified error signal to the main signal path;

an auxiliary circuit coupled to each of the main signal path and the feed forward correction circuit that receives a portion of the corrected output signal, detects a residual modulation in the corrected output signal, wherein the detected residual modulation corresponds to the reference modulation applied to the input signal, correlates the detected residual modulation and the reference signal to produce a correlation, generates at least one control signal based on the correlation, and conveys the at least one control signal to the feed forward correction circuit; and

wherein the feed forward correction circuit adjusts the error signal in response to receiving the at least one control signal, wherein, subsequent to the feed forward correction circuit adjusting the error signal, the main signal path decouples the reference modulation from the input signal and the auxiliary circuit holds the control signal constant, and wherein the feed forward amplifier tunes a carrier cancellation performance of the feed forward amplifier with the reference modulation decoupled from the input signal.

15. The feed forward amplifier of claim 14, wherein the auxiliary circuit comprises:

a reference modulation detector that receives the portion of the corrected output signal and detects the residual modulation in the corrected output signal;

a correlator that correlates the detected residual modulation and the reference signal to determine the correlation; and

a controller that produces the at least one control signal based on the correlation.

16. The feed forward amplifier of claim 15, wherein the feed forward correction circuit comprises:

a signal combiner that combines the at least a portion of the input signal with the portion of the amplified signal to determine the error signal;

a signal adjuster coupled to the signal combiner that adjusts the error signal based on the at least one control signal to produce an adjusted error signal; and

an error amplifier that amplifies the adjusted error signal to produce an amplified error signal.

17. The feed forward amplifier of claim 16, wherein the reference modulation comprises a reference amplitude modulation that is based on a first reference signal and a reference phase modulation that is based on a second reference signal, wherein the main signal path modulates an amplitude of the input signal with the reference amplitude modulation and modulates a phase of the input signal with the reference phase modulation, wherein the correlator correlates a detected residual amplitude reference modulation and the first reference signal to determine an amplitude correlation and correlates a detected residual phase reference modulation and the second reference signal to determine a phase correlation, wherein the controller produces an amplitude control signal based on the amplitude correlation and produces a phase control signal based on the phase correlation, and wherein the signal adjuster comprises an amplitude adjuster that adjusts an amplitude of the error signal based on the amplitude control signal and further comprises a phase adjuster that adjusts a phase of the error signal based on the phase control signal.

18. The feed forward amplifier of claim 17, wherein the first reference signal and the second reference signal each comprises a same pilot tone.

19. The feed forward amplifier of claim 16, wherein the reference modulation comprises a first reference modulation that is based on a first reference signal and a second reference modulation that is based on a second reference signal, wherein the main signal path modulates an in-phase component of the input signal with the first reference modulation and modulates a quadrature component of the input signal with the second reference modulation, wherein the correlator correlates a detected residual in-phase component reference modulation and the first reference signal to determine art in-phase correlation and correlates a detected residual quadrature component of reference modulation and the second reference signal to determine a quadrature correlation, wherein the controller produces an in-phase component control signal based on the in-phase correlation and produces a quadrature component control signal based on the quadrature correlation, and wherein the signal adjuster comprises an vector modulator that adjusts an amplitude of an in-phase component the error signal based on the in-phase component control signal and adjusts an amplitude of a quadrature component of the error signal based on the quadrature component control signal.

20. The feed forward amplifier of claim 19, wherein the first reference signal and the second reference signal each comprises a same pilot tone.