Feed-forward power amplifier system with adaptive control and control method

• US 5,485,120 A
• Filed: 07/28/1994
• Issued: 01/16/1996
• Est. Priority Date: 07/28/1994
• Status: Expired due to Fees

• Current Assignee: Helix, Inc., Weiss Peck & Greer Venture Associates III LP (Lightspeed Management Company, LLC), WPG Enterprise Fund II LP (Lightspeed Management Company, LLC)
• Original Assignee: Aval Communications, Inc.
• Inventors: Anvari, Kiomars
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US08/282,132
• Time in Patent Office: 537 Days
• Field of Search: 330/52, 330/107, 330/109, 330/149, 330/151
• US Class Current: 330/151
• CPC Class Codes: H03F 1/3235 using a pilot signal
• CPC Class Codes: H03F 2201/3212 Using a control circuit to adjust amplitude and phase of a signal in a signal path

Abstract

An adaptive control system and method for use with a feed-forward linear amplifier, and in particular a multi-channel linear amplifier wherein a distortion (error) detection circuit is used for detecting a nonlinear distortion component of a main amplifier output for using in correcting distortion in amplifying an information signal. The distortion correction can be extracted from a pilot signal, an analysis of distortion from a channel-by-channel sweep or from analysis of selected target channels. Analysis can be based on a single signal, an average of many signals, or a selection of maxima of one or many signals. Subharmonic sampling may be used in analog to digital conversion of an IF signal to detect for distortion within a passband.

Claims

1. In connection with a feed-forward linear amplifier having a main amplification path and a distortion signal path, said distortion signal path including means for controlling distortion signal delay and means for controlling distortion signal attenuation, an adaptive controller system for use in minimizing signal distortion of information signals applied through said linear amplifier, said adaptive controller system comprising:

means for continuously sampling analog signal output of said linear amplifier to produce an analog sampled signal;

means for downconverting said analog sampled signal to an IF band as a first analog IF signal;

first analog to digital converter means coupled to said downconverting means to convert said first analog IF signal to a first digitized IF signal;

means coupled to receive said first digitized IF signal for DSP processing said digitized IF signal to downconvert said digitized IF signal to a digitized baseband signal, to produce an in-phase component signal and a quadrature-phase component signal, and to generate from said in-phase component signal and said quadrature-phase component signal at least one error correction signal; and

means for applying said at least one error correction signal to said distortion signal delay controlling means and to said distortion signal attenuation controlling means for control in cancelling distortion in the information signal output of said linear amplifier.

2. The adaptive controller system according to claim 1, wherein said digitized IF signal is digitally sampled at a subharmonic of said IF signal.

3. The adaptive controller system according to claim 1, further including means for injecting a pilot signal into said information signal of said linear amplifier, and wherein said downconverting means is tuned to a frequency of said pilot signal to pass said pilot signal within a passband of said downconverting means.

4. The adaptive controller system according to claim 1, wherein said linear amplifier is a multi-channel amplifier, and wherein said downconverting means includes means for tuning across a range of channels for sampling on a channel-by-channel basis.

5. The adaptive controller system according to claim 1, wherein said linear amplifier is a multichannel amplifier, and wherein said downconverting means includes means for tuning to a limited selection of channels for sampling on a targeted channel basis.

6. The adaptive controller system according to claim 5, wherein said downconverting means includes a first mixer means in a first signal path coupled to said first analog to digital converter means, a second mixer means on a second signal path for generating a second analog IF signal;

further including a second analog to digital converter means coupled to said downconverting means to convert said second analog IF signal to a second digitized IF signal; and

switch means for selectively alternatively applying a representation of said analog sampled signal to said second mixer means along said second signal path and a representation of a distortion signal of said linear amplifier to said second mixer means along said second signal path for finding targeted channels and for generating a distortion sample signal for use in controlling phase delay and attenuation in said main amplification path.

7. The adaptive controller system according to claim 1, wherein said downconverting means includes a first mixer means in a first signal path coupled to said first analog to digital converter means, a second mixer means on a second signal path for generating a second analog IF signal;

further including a second analog to digital converter means coupled to said downconverting means to convert said second analog IF signal to a second digitized IF signal for continuously applying a representation of a distortion signal of said linear amplifier to said second mixer means along said second signal path for generating a distortion sample signal for use in controlling phase delay and attenuation in said main amplification path.

8. The apparatus according to claim 4 wherein said DSP processing means further includes means for producing a final error correction signal from averaging of measurements of said error correction signal on all channels to apply to said distortion signal delay means and said distortion signal attenuation means.

9. The apparatus according to claim 5 wherein said DSP processing means further includes means for producing a final error correction signal from averaging of measurements of said error correction signal on said targeted channels to apply to said distortion signal delay means and said distortion signal attenuation means.

10. The apparatus according to claim 6 wherein said DSP processing means further includes means for producing a final error correction signal from averaging of measurements of said error correction signal based on said pilot to apply to said distortion signal delay means and said distortion signal attenuation means.

11. The apparatus according to claim 4 wherein said DSP processing means further includes means for producing a final error correction signal from measurements of maxima of said error correction signal on all channels to apply to said distortion signal delay means and said distortion signal attenuation means.

12. The apparatus according to claim 5 wherein said DSP processing means further includes means for producing a final error correction signal from measurements maxima of said error correction signal on said targeted channels to apply to said distortion signal delay means and said distortion signal attenuation means.

13. The apparatus according to claim 6 wherein said DSP processing means further includes means for producing a final error correction signal from measurements of maxima of said error correction signal based on said pilot to apply to said distortion signal delay means and said distortion signal attenuation means.

27. In connection with a feed-forward linear amplifier having a main amplification signal path and a distortion signal path according to claim 1, said main amplification signal path including means for controlling main signal delay and means for controlling main signal attenuation, an adaptive controller system for use in extracting from a representation of said main amplification signal path a substantially pure distortion signal for application to said distortion signal path, said adaptive controller system comprising:

means for continuously sampling analog signal output of said linear amplifier to produce an output analog sampled signal;

means for subtracting said output analog sampled signal from a representation of an input signal to said feed-forward linear amplifier to produce said distortion signal;

means for sampling said distortion signal to produce a continuously-sampled distortion signal;

means coupled to receive said continuously-sampled distortion signal for downconverting said continuously-sampled distortion signal to an IF band as a second analog IF signal;

second analog to digital converter means coupled to said downconverting means to convert said second analog IF signal to a second digitized IF signal;

means coupled to receive said second digitized IF signal for DSP processing said second digitized IF signal to downconvert said second digitized IF signal to a second digitized baseband signal, to produce a distortion in-phase component signal and a distortion quadrature-phase component signal, and to generate from said distortion in-phase component signal and said distortion quadrature-phase component signal at least one distortion error correction signal; and

means for applying said at least one distortion error correction signal to said main signal delay controlling means and to said main signal attenuation controlling means for control in cancelling information signal output in said distortion signal path to yield said substantially pure distortion signal.

14. In connection with a feed-forward linear amplifier having a main amplification path and a distortion signal path, said distortion signal path including means for controlling distortion signal delay and means controlling distortion signal attenuation, a method for adaptive control of said linear amplifier to minimize signal distortion of information signals applied through said linear amplifier, comprising the steps of:

continuously sampling analog signal output of said linear amplifier to produce an analog sampled signal;

downconverting said analog sampled signal to an IF band as a first analog IF signal;

converting said first analog IF signal to a first digitized IF signal;

downconverting said digitized IF signal to a digitized baseband signal, to produce an in-phase component signal and a quadrature-phase component signal, and to generate from said in-phase component signal and said quadrature-phase component signal at least one error correction signal; and

applying said at least one error correction signal to a distortion signal delay controlling means and to a distortion signal attenuation controlling means for control in cancelling distortion in the information signal output of said linear amplifier.

15. The method according to claim 14, wherein said digitized IF signal is digitally sampled at a subharmonic of said IF signal.

16. The method according to claim 14, further including the steps of injecting a pilot signal into said information signal of said linear amplifier, and of tuning said downconverting means to a frequency of said pilot signal to pass said pilot signal within a passband of said downconverting means.

17. The method according to claim 14, wherein said linear amplifier is a multichannel amplifier, further including the step of tuning said downconverting means across a range of channels for sampling on a channel-by-channel basis.

18. The method according to claim 14, wherein said linear amplifier is a multichannel amplifier, further including the step of tuning said downconverting means to a limited selection of channels for sampling on a targeted channel basis.

19. The method according to claim 18, wherein said downconverting step includes the step of mixing signals in a first signal path and mixing signal in a second signal path for generating a second analog IF signal;

converting said second analog IF signal to a second digitized IF signal; and

selectively alternatively applying a representation of said analog sampled signal for said mixing along said second signal path and a representation of a distortion signal of said linear amplifier for mixing along said second signal path for finding targeted channels and for generating a distortion sample signal for use in controlling phase delay and attenuation in said main amplification path.

20. The method according to claim 14, wherein said downconverting step includes mixing signals in a first signal path for generating said first analog IF signal and mixing signals in a second signal path for generating a second analog IF signal;

converting said second analog IF signal to a second digitized IF signal for continuously applying a representation of a distortion signal of said linear amplifier to said second mixer means along said second signal path for generating a distortion sample signal for use in controlling phase delay and attenuation in said main amplification path.

21. The method according to claim 17 wherein said DSP processing further includes producing a final error correction signal from averaging of measurements of said error correction signal on all channels to apply to said distortion signal delay means and said distortion signal attenuation means.

22. The method according to claim 18 wherein said DSP processing further includes producing a final error correction signal from averaging of measurements of said error correction signal on said targeted channels to apply to said distortion signal delay means and said distortion signal attenuation means.

23. The method according to claim 19 wherein said DSP processing further includes producing a final error correction signal from averaging of measurements of said error correction signal based on said pilot to apply to said distortion signal delay means and said distortion signal attenuation means.

24. The method according to claim 17 wherein said DSP processing further includes producing a final error correction signal from measurements of maxima of said error correction signal on all channels to apply to said distortion signal delay means and said distortion signal attenuation means.

25. The method according to claim 18 wherein said DSP processing further includes producing a final error correction signal from measurements maxima of said error correction signal on said targeted channels to apply to said distortion signal delay means and said distortion signal attenuation means.

26. The method according to claim 19 wherein said DSP processing further includes producing a final error correction signal from measurements of maxima of said error correction signal based on said pilot to apply to said distortion signal delay means and said distortion signal attenuation means.

28. In connection with a feed-forward linear amplifier having a main amplification signal path and a distortion signal path, said main amplification signal path including means for controlling main signal delay and means for controlling main signal attenuation, an adaptive controller system for use in extracting from a representation of said main amplification signal path a substantially pure distortion signal for application to said distortion signal path, said adaptive controller system comprising:

means for continuously sampling analog signal output of said linear amplifier to produce an output analog sampled signal;

means for subtracting said output analog sampled signal from a representation of an input signal to said feed-forward linear amplifier to produce said distortion signal;

means for sampling said distortion signal to produce a continuously-sampled distortion signal;

means coupled to receive said continuously-sampled distortion signal for downconverting said continuously-sampled distortion signal to an IF band as a second analog IF signal;

second analog to digital converter means coupled to said downconverting means to convert said second analog IF signal to a second digitized IF signal;

means coupled to receive said second digitized IF signal for DSP processing said second digitized IF signal to downconvert said second digitized IF signal to a second digitized baseband signal, to produce a distortion in-phase component signal and a distortion quadrature-phase component signal, and to generate from said distortion in-phase component signal and said distortion quadrature-phase component signal at least one distortion error correction signal; and

means for applying said at least one distortion error correction signal to said main signal delay controlling means and to said main signal attenuation controlling means for control in cancelling information signal output in said distortion signal path to yield said substantially pure distortion signal.

29. In connection with a feed-forward linear amplifier having a main amplification signal path and a distortion signal path, said main amplification signal path including means for controlling main signal delay and means for controlling main signal attenuation, a method for extracting from a representation of said main amplification signal path a substantially pure distortion signal for application to said distortion signal path, said method comprising the steps of:

continuously sampling analog signal output of said linear amplifier to produce an output analog sampled signal;

subtracting said output analog sampled signal from a representation of an input signal to said feed-forward linear amplifier to produce said distortion signal;

sampling said distortion signal to produce a continuously-sampled distortion signal;

downconverting said continuously-sampled distortion signal to an IF band as a second analog IF signal;

converting said second analog IF signal to a second digitized IF signal;

DSP processing said second digitized IF signal to downconvert said second digitized IF signal to a second digitized baseband signal, to produce a distortion in-phase component signal and a distortion quadrature-phase component signal, and to generate from said distortion in-phase component signal and said distortion quadrature-phase component signal at least one distortion error correction signal; and

applying said at least one distortion error correction signal to control delay in said main signal path and to control attenuation in said main signal path in order to control cancelling of information signal output in said distortion signal path to yield said substantially pure distortion signal.