Feed-forward amplifier

• US 6,392,483 B2
• Filed: 05/15/2001
• Issued: 05/21/2002
• Est. Priority Date: 05/18/2000
• Status: Expired due to Term

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Suzuki, Yasunori, Nojima, Toshio
• Primary Examiner(s): Lee, Benny
• Assistant Examiner(s): Choe, Henry
• Application Number:
  US09/854,476
• Publication Number:
  US 20010043118A1
• Time in Patent Office: 371 Days
• Field of Search: 330/52, 330/149, 330/151
• US Class Current: 330/151
• CPC Class Codes: H03F 1/3235 using a pilot signal
• CPC Class Codes: H03F 1/3252 using multiple parallel paths between input and output H03F1/3258, H03F1/3282, H03F1/3294 take precedence
• CPC Class Codes: H03F 2201/3212 Using a control circuit to adjust amplitude and phase of a signal in a signal path
• CPC Class Codes: H03F 2201/3218 the main amplifier or error amplifier being a feedforward amplifier

Abstract

In a feed-forward amplifier a signal power dynamic range compressing circuit for compressing the power dynamic range of the input signal to the feed-forward amplifier is provided in a distortion detecting loop at the input side of a main amplifier, and the output backoff of the main amplifier is reduced to thereby achieve high-efficiency amplification of the feed-forward amplifier.

Claims

1. A feed-forward amplifier for amplifying a power of an input transmission signal and including a distortion detecting loop for detecting a distortion component and a distortion canceling loop cascade-connected to said distortion detecting loop for canceling said distortion component, wherein:

said distortion detecting loop comprises;

a main amplifier path containing a main amplifier;

a signal power dynamic range compressing circuit inserted in said main amplifier path at an input side of said main amplifier, for compressing a power dynamic range of said input transmission signal;

a first linear signal transfer path;

a first directional coupler for distributing said input transmission signal to said main amplifier path and said first linear signal transfer path; and

a second directional coupler for power-combining output signals from said main amplifier path and said first linear signal transfer path and for dividing said combined output signal into first and second combined outputs, said distortion canceling loop comprises;

a second linear signal transfer path supplied with the first combined output from said second directional coupler, for transferring said supplied first combined output;

an auxiliary amplifier path containing an auxiliary amplifier and supplied with the second combined output from said second directional coupler, for transferring said supplied second combined output; and

a third directional coupler for power-combining outputs from said second linear signal transfer path and said auxiliary amplifier path and for outputting said power-combined transmission signal, and

said signal power dynamic range compressing circuit comprises;

a fourth directional coupler for dividing a signal on said main amplifier path into first and second signals and for outputting said first and second divided signals;

a third linear signal transfer path for linearly transferring the first divided signal from said fourth directional coupler;

a compressing signal generator for generating a compressing signal that makes an envelope of said first divided signal constant based on the second divided signal from said fourth directional coupler; and

a fifth directional coupler for power-combining an output signal from said third linear signal transfer path and said compressing signal from said compressing signal generator and for providing said power-combined output to said main amplifier.

2. The amplifier of claim 1, wherein said compressing signal generator comprises:

a level discriminator for detecting a peak power of said input transmission signal above a predetermined level;

a peak power detector for detecting a phase of said input transmission signal in response to the detection of said peak power;

a low-frequency oscillator for generating a low-frequency signal that is nearly 180°

out of phase with said detected phase; and

a frequency converter for frequency-converting said low-frequency signal to a desired frequency band and for outputting said frequency-converted signal as said compressing signal.

3. The amplifier of claim 1, wherein said compressing signal generator comprises:

a level discriminator for detecting a peak power of said input transmission signal above a predetermined level;

a peak power detector for detecting an amplitude of said input transmission signal in response to the detection of said peak power;

a low-frequency oscillator in which said detected amplitude is set, for generating a low-frequency signal that is nearly 180°

out of phase with a phase of said input transmission signal; and

a frequency converter for frequency-converting said low-frequency signal to a desired frequency band and for outputting said frequency-converted signal as said compressing signal.

4. The amplifier of claim 1, wherein said compressing signal generator comprises:

a level discriminator for detecting a peak power of said input transmission signal above a predetermined level;

a peak power detector for detecting a phase and amplitude of said input transmission signal in response to the detection of said peak power;

a low-frequency oscillator for generating a low-frequency signal that is nearly 180°

out of phase with said detected phase;

a modulating signal generating means for generating a predetermined modulating signal;

a modulator circuit for modulating said low-frequency signal with said modulating signal to generate a modulated low-frequency signal; and

a frequency converter for frequency-converting said modulated low-frequency signal to a desired frequency band and for outputting said frequency-converted signal as said compressing signal.

5. The amplifier of claim 4, wherein said modulating signal generating means is a code generator for generating a code of a specific pattern as said modulating signal.

6. The amplifier of any one of claims 1 to 4, wherein said compressing signal generator comprises a variable phase shifter for adjusting the phase of said compressing signal and variable amplitude means for adjusting the amplitude of said compressing signal, and said signal power dynamic range compressing circuit further comprises a compressing signal adjustment part for controlling said variable phase shifter and said variable amplitude means so that the peak power of said combined signal distributed from said main amplifier goes down below a preset value.

7. The amplifier of claim 6, wherein said compressing signal adjustment part comprises:

combined signal level discriminating means for discriminating a level of said distributed combined signal above a predetermined value;

a combined signal peak power detector for detecting a phase and amplitude of said distributed combined signal in response to the detection of the level above said predetermined value; and

a control circuit for adjusting said variable phase shifter and said variable amplitude means based on said detected phase and amplitude of said distributed combined signal so that the level of said distributed combined signal goes down below said predetermined value.

8. The amplifier of claim 1, wherein said compressing signal generator comprises:

a quadrature detector for quadrature-detecting said input transmission signal and for outputting its phase and amplitude;

a constant-envelope signal generator for generating from said phase and amplitude of the input transmission signal a signal for making the input transmission signal have a constant envelope; and

a frequency converter for converting said signal from said constant-envelope signal generator to a desired frequency band and for outputting said frequency-converted signal as said compressing signal.

9. The amplifier of claim 1, wherein said compressing signal generator comprises:

an envelope detector for envelope-detecting said input transmission signal and for outputting its phase and amplitude;

a constant-envelope signal generator for generating from said phase and amplitude of the input transmission signal a signal for making the input transmission signal have a constant envelope; and

a frequency converter for converting said signal from said constant-envelope signal generator to a desired frequency band and for outputting said frequency-converted signal as said compressing signal.

10. The amplifier of claim 8 or 9, wherein said compressing signal generator comprises a variable phase shifter for adjusting the phase of said compressing signal and variable amplitude means for adjusting the amplitude of said compressing signal, and said signal power dynamic range compressing signal further comprises a compressing signal adjustment part for controlling said variable phase shifter and said variable amplitude means so that the peak power of said combined signal distributed from said main amplifier goes down below a preset value.

11. The amplifier of claim 10, wherein said compressing signal adjustment part comprises peak-to-average power ratio detecting means for detecting a peak-to-average power ratio of said distributed combined signal above a predetermined value, and a control circuit for adjusting said variable phase shifter and said variable amplitude means in response to the detection of said peak-to-average power ratio above said predetermined value so that said peak-to-average power ratio of said distributed combined signal goes down below said predetermined value.

12. The amplifier of claim 2 or 3, wherein said signal power dynamic range compressing circuit further comprises a compressing signal adjustment part for controlling said low-frequency oscillator so that the peak power of said combined signal distributed from said power combiner goes down below a predetermined value.

13. The amplifier of claim 12, wherein said compressing signal adjustment part comprises:

combined signal level discriminating means for discriminating a level of said distributed combined signal above a predetermined value;

a combined signal peak power detector for detecting the phase and amplitude of said distributed combined signal in response to the detection of the level above said predetermined value; and

a control circuit for adjust said variable phase shifter and said variable amplitude means based on said detected phase and amplitude of said distributed combined signal so that the level of said distributed combined signal goes down below said predetermined value.

14. The amplifier of claim 8 or 9, wherein said signal power dynamic range compressing circuit further comprises a compressing adjustment part for controlling said constant-envelope signal generator so that a peak-to-average power ratio of said combined signal distributed from said power combiner goes down below a predetermined value.

15. The amplifier of claim 14, wherein said compressing signal adjustment part comprises peak-to-average power ratio detecting means for detecting the peak-to-average power ratio of said distributed combined signal above a predetermined value, and a control circuit for adjusting said variable phase shifter and said variable amplitude means in response to the detection of said peak-to-average power ratio above said predetermined value so that said peak-to-average power ratio of said combined signal goes down below said predetermined value.

16. The amplifier of any one of claims 2, 3, 4, 8 or 9, wherein said frequency converter frequency-converts said low-frequency signal to a frequency band different from that of said input transmission signal.

17. The amplifier of any one of claims 2, 3, 4, 8 or 9, wherein said frequency converter frequency-converts said low-frequency signal to a frequency band identical with that of said input signal.

18. The amplifier of any one of claims 1, 2, 3, 4, 8, or 9, further comprising:

means for generating a first pilot signal;

means for injecting said first pilot signal into an input path of said distortion detecting loop;

first electrically variable attenuator means and first electrically variable phase shifter means inserted in said distortion detecting loop;

means for generating a second pilot signal;

means inserted in a path of said main amplifier of said distortion detecting loop, for injecting said second pilot signal into said main amplifier;

means inserted in said distortion canceling loop, for detecting said first pilot signal;

second electrically variable attenuator and second electrically variable phase shifter means inserted in said distortion canceling loop;

means inserted in an output path of said distortion canceling loop, for detecting said second pilot signal;

first level detecting means for detecting a level of said detected first pilot signal;

second level detecting means for detecting a level of said detected second pilot signal; and

control means for controlling said first electrically variable attenuator means and said first electrically phase shifter means in a manner to minimize the detected level by said first level detecting means, and for controlling said second electrically variable attenuator means and said second electrically phase shifter means in a manner to minimize the detected level by said second level detecting means.

19. The amplifier of any one of claims 1, 2, 3, 4, 8 and 9, wherein said main amplifier is a saturation amplifier.

20. The amplifier of any one of claims 1, 2, 3, 4, 8 or 9, further comprising voltage control means for controlling a voltage to be applied to a semiconductor device of said main amplifier.

21. A power amplifying method for power-amplifying an input transmission signal by a feed-forward amplifier provided with a distortion detecting loop for detecting a distortion component and a distortion canceling loop cascade-connected to said distortion detecting loop, for canceling said distortion component, said method comprising the steps of:

(a) distributing said input transmission signal to a first linear signal transfer path and a main amplifier path;

(b) distributing said input transmission signal, distributed to said main amplifier, to a second linear signal transfer path and a compressing signal generating path;

(c) generating, based on said input transmission signal distributed to said compressing signal generating path, a compressing signal for making a constant-envelope said signal distributed to said second linear signal transfer path;

(d) power-combining said compressing signal and an output from said second linear signal transfer path and power-amplifying said combined signal by a main amplifier of said main amplifier path;

(e) power-combining an output from said main amplifier path and an output from said first linear signal transfer path and distributing said power-combined signal to a third linear signal transfer path and an auxiliary amplifier path; and

(f) power-combining an output from said auxiliary amplifier path and an output from said third linear signal transfer path to cancel a distortion component of said input transmission signal transferred over said third linear signal transfer path and outputting said input transmission signal amplified in power.

22. The method of claim 21, wherein said step (c) is a step of detecting a peak power of said signal distributed to said compressing signal generating path and generating said compressing signal for compressing the peak power of said signal distributed to said second linear signal transfer path.

23. The method of claim 21, wherein said step (c) is a step of detect a peak-to-average power ratio of said signal distributed to said compressing signal generating path and generating said compressing signal for compressing the peak-to-average power ratio of said signal distributed to said second linear signal transfer path.