Digital predistortion for amplifiers

• US 6,304,140 B1
• Filed: 06/12/2000
• Issued: 10/16/2001
• Est. Priority Date: 06/12/2000
• Status: Expired due to Fees

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Anderson, David J., Thron, Christopher P., Thomas, Michael B.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Nguyen, Patricia T.
• Application Number:
  US09/592,216
• Time in Patent Office: 491 Days
• Field of Search: 330/2, 330/149, 375/296, 375/297
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3282 Acting on the phase and the amplitude of the input signal

Abstract

A method for predistorting a digital signal prior to amplification is disclosed in which a look-up table is computed using power values of digital input signal samples as look-up values. The look-up table is preferably a function of pre-measured calibration data. The look-up table is applied to digital input signals for producing the predistorted signal. Computing the look-up table may include determining a set of input power values, obtaining the pre-measured calibration data including an output power data value and phase data value of the amplifier corresponding to each of the input power values, and deriving a set of calibration power values using the output power data values. The calibration power values and the input power values are then used to derive amplitude predistortion calibration values while the phase data values are used to determine phase predistortion calibration values. The calibration power values and corresponding amplitude predistortion calibration values are interpolated to provide amplitude predistortion values while the calibration power values and corresponding phase predistortion calibration values are interpolated to provide phase predistortion values. The look-up table is computed from the amplitude predistortion values and the phase predistortion values.

Claims

1. A method for predistorting a digital signal prior to amplification comprising:

computing a look-up table using power values of digital input signal samples as look-up values wherein the look-up table is a function of pre-measured calibration data;

wherein the step of computing comprises;

determining a set of input power values;

obtaining the pre-measured calibration data including an output power data value and phase data value of the amplifier corresponding to each of the input power values;

deriving a set of calibration power values using the output power data values;

deriving amplitude predistortion calibration values using the calibration power values and the input power values;

determining phase predistortion calibration values from the phase data values;

interpolating the calibration power values and corresponding amplitude predistortion calibration values to provide amplitude predistortion values;

interpolating the calibration power values and corresponding phase predistortion calibration values to provide phase predistortion values; and

wherein the look-up table is computed from the amplitude predistortion values and the phase predistortion values; and

applying the look-up table to digital input signals for producing the predistorted signal;

wherein,

the amplitude predistortion values and the phase predistortion values are polar values, the method further comprising;

translating the amplitude predistortion values and the phase predistortion values from polar values to Cartesian values.

2. A method for predistorting a digital signal prior to amplification comprising:

computing a look-up table using power values of digital input signal samples as look-up values wherein the look-up table is a function of pre-measured calibration data;

applying the look-up table to digital input signals for producing the predistorted signal; and

changing all the look-up values in response to a change in only one parameter, wherein the change in the one parameter is a measure of a change in amplification.

3. The method of claim 2, wherein the step of computing the look-up table further comprises:

determining a set of input power values;

obtaining the pre-measured calibration data including an output power data value and phase data value of the amplifier corresponding to each of the input power values;

deriving a set of calibration power values using the output power data values;

deriving amplitude predistortion calibration values using the calibration power values and the input power values;

determining phase predistortion calibration values from the phase data values;

interpolating the calibration power values and corresponding amplitude predistortion calibration values to provide amplitude predistortion values wherein the amplitude predistortion values are polar values;

interpolating the input power values and corresponding phase predistortion calibration values to provide phase predistortion values wherein the phase predistortion values are polar values;

translating the phase predistortion values from polar values to Cartesian values; and

wherein the look-up table is computed from the amplitude predistortion values and the phase predistortion values.

4. A method for predistorting a digital signal prior to amplification comprising:

computing a look-up table using power values of digital input signal samples as look-up values wherein the look-up table is a function of pre-measured calibration data;

applying the look-up table to digital input signals for producing the predistorted signal; and

changing all the look-up values in response to a change in only a pair of parameters, wherein the change in the pair of parameters is a measure of a change in amplification.

5. The method of claim 4, wherein the step of computing the look-up table further comprises:

determining a set of input power values;

obtaining the pre-measured calibration data including an output power data value and phase data value of the amplifier corresponding to each of tile input power values;

deriving a set of calibration power values using the output power data values;

deriving amplitude predistortion calibration values using the calibration power values and the input power values;

determining phase predistortion calibration values from the phase data values;

interpolating the calibration power values and corresponding amplitude predistortion calibration values to provide amplitude predistortion values wherein the amplitude predistortion values are polar values;

interpolating the calibration power values and corresponding phase predistortion calibration values to provide phase predistortion values wherein the phase predistortion values are polar values;

translating the phase predistortion values from polar values to Cartesian values; and

wherein the look-up table is computed from the amplitude predistortion values and the phase predistortion values.

6. A method for linearizing an amplifier to produce an amplified output signal comprising:

predistorting a signal prior to amplification comprising;

computing a look-up table using power values of digital input signal samples as look-up values wherein the look-up table is a function of pre-measured calibration data;

wherein the step of computing the look-up table further comprises;

determining a set of input power values;

obtaining the pre-measured calibration data including an output power data value and phase data value of the amplifier corresponding to each of the input power values;

deriving a set of calibration power values using the output power data values;

deriving amplitude predistortion calibration values using the calibration power values and the input power values;

determining phase predistortion calibration values from the phase data values;

interpolating the calibration power values and corresponding amplitude predistortion calibration values to provide amplitude predistortion values;

interpolating the calibration power values and corresponding phase predistortion calibration values to provide phase predistortion values; and

wherein the look-up table is computed from the amplitude predistortion values and the phase predistortion values; and

applying the look-up table to digital input signals for producing the predistorted signal;

wherein the amplitude predistortion values and the phase predistortion values are polar values, the method further comprising;

translating the amplitude predistortion values and the phase predistortion values from polar values to Cartesian values.

7. The method of claim 6, further comprising:

up-converting the digital input signals; and

producing an output signal which is linearly related to the digital input signal after amplification of the predistorted signal.

8. The method of claim 6, further comprising:

adapting the look-up values in response to changes in amplification using a single constant.

9. The method of claim 6, further comprising:

adapting the look-up values in response to changes in amplification using a pair of constants.

10. A method for linearizing an amplifier to produce an amplified output signal comprising:

computing a look-up table including;

determining a set of input power values;

obtaining an output power value and phase value of the amplifier corresponding to each of the input power values;

deriving a set of calibration power values using the output power values;

deriving amplitude predistortion calibration values using the calibration power values and the input power values;

determining phase predistortion calibration values from the phase values;

interpolating the calibration power values and corresponding amplitude predistortion calibration values to provide amplitude predistortion values;

interpolating the calibration power values and corresponding phase predistortion calibration values to provide phase predistortion values; and

wherein the look-up table is computed from the amplitude predistortion values and the phase predistortion values; and

applying the look-up table to a digital input signal for producing a predistorted signal;

amplifying the predistorted signal;

producing an output signal which is linearly related to the digital input signal; and

translating the amplitude predistortion values and the phase predistortion values from polar values to Cartesian values.

11. A method for linearizing an amplifier to produce an amplified output signal from a set of carrier frequencies, the method comprising:

linearly combining a set of digital baseband signals corresponding to the set of carrier frequencies to produce an extended digital baseband signal;

wherein the step of linearly combining the set of digital baseband signals further comprises;

complex mixing individual digital baseband signals of the set of digital baseband signals with trigonometric signals to produce complex mixed signals; and

adding the complex mixed signals to produce the extended digital baseband signal;

deriving look-up values from the power values of the extended digital baseband signal for applying to a look-up table to obtain predistortion values, wherein the look-up table is a function of pre-measured calibration data;

producing one or more predistorted signals by complex mixing the predistortion values with a selected one of the extended digital baseband signal and the set of digital baseband signals; and

producing the amplified output signal which is linearly related to the set of digital baseband signals.

12. The method of claim 11, wherein the step of producing one or more predistorted signals further comprises:

up-converting the predistorted signals synchronously when said predistorted signals are a complex mixing of the predistortion values and the set of digital baseband signals.

13. A semiconductor device comprising:

a memory for storing a look-up table wherein the look-up table is a function of pre-measured calibration data, and wherein the look-up table uses power values of digital input signal samples as look-up values;

a complex mixer for applying the look-up table to digital input signals for producing a predistorted signal;

wherein the complex mixer further comprises;

a plurality of multipliers;

an amplifier for receiving and amplifying the predistorted signal; and

wherein an amplified output signal is produced which is linearly related to the digital input signals.

14. The semiconductor device of claim 13, further comprising:

a converter for converting the predistorted signal from digital to analog; and

an upconverter for upconverting the predistorted signal from baseband to carrier band.

15. The semiconductor device of claim 13, further comprising:

a power value estimator for providing a set of input power values to the look-up table.

16. The semiconductor device of claim 13, wherein the look-up values are adapted in response to changes in amplification using a single constant.

17. A semiconductor device comprising:

a memory for storing a look-up table wherein the look-up table is a function of pre-measured calibration data, and wherein the look-up table uses power values of digital input signal samples as look-up values;

a complex mixer for applying the look-up table to digital input signals for producing a predistorted signal;

an amplifier for receiving and amplifying the predistorted signal; and

wherein an amplified output signal is produced which is linearly related to the digital input signals; and

wherein the look-up values are adapted in response to changes in amplification using a pair of constants.