High-efficiency linear power amplifier

• US 7,042,283 B2
• Filed: 03/23/2004
• Issued: 05/09/2006
• Est. Priority Date: 03/24/2003
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Mizuta, Shinji, Hirota, Tetsuo, Yamao, Yasushi, Suzuki, Yasunori
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Flanagan, Krista M.
• Application Number:
  US10/806,245
• Publication Number:
  US 20040189378A1
• Time in Patent Office: 777 Days
• Field of Search: None
• US Class Current: 330/52
• CPC Class Codes: H03F 1/0288 using a main and one or several auxiliary peaking amplifiers whereby the load is connected to the main amplifier using an impedance inverter, e.g. Doherty amplifiers
• CPC Class Codes: H03F 1/3258 based on polynomial terms
• CPC Class Codes: H03F 2200/393 A measuring circuit being coupled to the output of an amplifier
• CPC Class Codes: H03F 3/24 of transmitter output stages

Abstract

A transmission signal and a pilot signal are predistorted by a digital predistorter 13 by use of a power-series model, and the predistorted output is converted by a digital-analog converter 14 to an analog signal. The analog signal is up converted by a frequency converter 15 to an RF-band signal, which is transmitted after being power-amplified by a Doherty amplifier 16. The pilot signal is extracted by a pilot signal extractor 17 from the output from the Doherty amplifier, and the extracted pilot signal is down converted by a frequency converter 18 to a baseband signal. The baseband pilot signal is converted by an analog-digital converter 19 to a digital pilot signal. A control part 21 detects an odd-order distortion component from the digital pilot signal, and based on the detected result, controls parameters of the digital predistorter.

Claims

1. A high-efficiency linear power amplifier comprising:

a digital predistorter for predistorting an input digital transmission signal thereto by use of a power-series model;

a digital-analog converter for converting the output from said digital predistorter to an analog signal;

an up converting part for frequency-converting the output from said digital-analog converter to a radio-frequency signal;

a Doherty amplifier for power-amplifying said radio-frequency signal and for transmitting said power-amplified radio-frequency signal;

a pilot signal generator for generating a digital pilot signal;

an adder for adding said digital pilot signal to said digital transmission signal and for inputting the added output to said digital predistorter;

a pilot signal extractor for extracting a radio-frequency pilot signal from the output from said Doherty amplifier;

a down converting part for frequency-converting said extracted pilot signal to a baseband extracted pilot signal;

an analog-digital converter for converting said baseband extracted pilot signal to a digital extracted pilot signal; and

a control part for detecting an odd-order distortion component from said digital extracted pilot signal and for controlling parameters of said digital predistorter based on the detected odd-order distortion component.

3. The high-efficiency linear power amplifier of claim 1 or 2, wherein said digital predistorter comprises:

a linear path for linear transfer of an input signal;

a nonlinear path for imparting an odd-order distortion to said input signal;

a delay memory inserted in said linear path, for providing the same delay as in said nonlinear path;

an odd-order distortion generator inserted in said nonlinear path, for generating an odd-order distortion component of said input signal; and

a vector adjuster inserted in said nonlinear path, for adjusting the amplitude and phase of said odd-order distortion component.

4. The high-efficiency linear power amplifier of claim 1 or 2, wherein said digital predistorter comprises:

a linear path for linear transfer of an input signal;

a nonlinear path for imparting an odd-order distortion to said input signal;

a delay memory inserted in said linear path, for providing the same delay as in said nonlinear path;

an odd-order distortion generator inserted in said nonlinear path, for generating an odd-order distortion component of said input signal; and

a vector adjuster inserted in said nonlinear path, for adjusting the amplitude and phase of said odd-order distortion component; and

wherein

said control part comprises;

an odd-order distortion component extracting part for extracting the odd-order distortion component from said extracted pilot signal;

a distortion component detector for detecting the level and phase of said extracted odd-order distortion component; and

an amplitude/phase controller for controlling said vector adjuster inserted in said nonlinear path of said digital predistorter based on the detected level and phase.

5. The high-efficiency linear power amplifier of claim 1 or 2, wherein said Doherty power amplifier comprises:

a peak amplifier that performs a class “

C”

operation when the amplitude of an input signal is above a predetermined threshold value; and

a carrier amplifier that performs a class “

B”

operation at all times.

6. The high-efficiency linear power amplifier of claim 3, further comprising a frequency characteristic compensator inserted in said nonlinear path at at least one of input and output sides of said odd-order distortion generator, for imparting a frequency characteristic to said input signal to compensate for the frequency characteristic of a distortion produced by said Doherty power amplifier.

7. The high-efficiency linear power amplifier of claim 6, wherein said frequency characteristic compensator is an FIR filter.

8. The high-efficiency linear power amplifier of claim 6, wherein said frequency characteristic compensator comprises:

a fast Fourier transformer for transforming said input signal to a frequency domain signal;

another vector adjuster for adjusting the amplitude and phase of said frequency domain signal; and

an inverse fast Fourier transformer for transforming said adjusted frequency domain signal to a time domain signal and for providing said time domain signal as the output from said frequency characteristic compensator.

9. The high-efficiency linear power amplifier of claim 4, wherein said odd-order distortion component extracting part is a band-pass filter that permits the passage therethrough of the frequency of said odd-order distortion component.

10. The high-efficiency linear power amplifier of claim 4, wherein said odd-order distortion component extracting part comprises:

a linear path for transmitting said digital pilot signal with a predetermined delay;

an odd-order distortion component generator for generating an odd-order distortion component different from said odd-order distortion component of said digital pilot signal;

a nonlinear path having inserted therein a variable phase shifter and a variable gain adjuster for adjusting the phase and gain of said odd-order distortion component; and

subtracting means for subtracting the outputs from said linear path and said nonlinear path from said digital extracted pilot signal provided from said analog-digital converter to extract said odd-order distortion component.

2. A high-efficiency linear power amplifier comprising:

a digital predistorter for predistorting an input digital transmission signal thereto by use of a power-series model;

a digital-analog converter for converting the output from said digital predistorter to an analog signal;

an up converting part for frequency-converting the output from said digital-analog converter to a radio-frequency signal; and

a Doherty amplifier for power-amplifying said radio-frequency signal and for transmitting said power-amplified radio-frequency signal;

a pilot signal generator for generating a digital pilot signal;

another digital predistorter for predistorting said digital pilot signal by use of a power-series model to provide a pilot signal added with an odd-order distortion component;

another digital-analog converter for converting said pilot signal added with the odd-order distortion component to an analog pilot signal;

an adder for adding together said analog signal from said digital-analog converter and said analog pilot signal from said another digital-analog converter and for applying the added output as an input signal to said up converting part;

a pilot signal extractor for extracting a radio-frequency pilot signal from the output from said Doherty amplifier;

a down converting part for frequency-converting said extracted pilot signal to a baseband extracted pilot signal;

an analog-digital converter for converting said baseband extracted pilot signal to a digital extracted pilot signal; and

a control part for detecting an odd-order distortion component from said digital extracted pilot signal and for controlling parameters of said digital predistorter and said another digital predistorter based on the detected odd-order distortion components.