WIDEBAND DIGITAL PREDISTORTION

• US 20170338841A1
• Filed: 05/19/2016
• Published: 11/23/2017
• Est. Priority Date: 05/19/2016
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Inventors: Pratt, Patrick
• Granted Patent: US 10,224,970 B2
• Time in Patent Office: Days
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion
• CPC Class Codes: H04L 2025/03356 Baseband transmission
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

Various examples are directed to systems and methods for wideband digital predistortion. A digital pre-distortion circuit may be programmed to receive a complex baseband signal and generate a pre-distorted signal. Generating the pre-distorted signal may comprise applying to the complex baseband signal a first correction for an N^th order distortion of a power amplifier at an I^th harmonic frequency zone centered at about an I^th harmonic of a carrier frequency and applying to the complex baseband signal a second correction for the N^th order distortion at a J^th harmonic frequency zone centered at about a J^th harmonic of the carrier frequency different than the I^th harmonic of a carrier frequency.

Claims

1. A system comprising:

a digital pre-distortion circuit programmed to;

receive a complex baseband signal; and

generate a pre-distorted signal, the generating of the pre-distorted signal comprising;

applying to the complex baseband signal a first correction for an N^th order distortion of a power amplifier at an I^th harmonic frequency zone centered at about an I^th harmonic of a carrier frequency; and

applying to the complex baseband signal a second correction for the N^th order distortion at a J^th harmonic frequency zone centered at about a J^th harmonic of the carrier frequency different than the I^th harmonic of the carrier frequency.

2. The system of claim 1, wherein the digital pre-distortion circuit is further programmed to:

determine a value for a first complex basis function for the N^th order distortion at the I^th harmonic frequency zone based at least in part on the complex baseband signal;

determine a value for a second complex basis function for the Nth order distortion at the I^th harmonic frequency zone based at least in part on the complex baseband signal;

apply a first finite impulse response (FIR) filter to generate a first FIR response based at least in part on the value for the first complex basis function; and

apply a second FIR filter to generate a second FIR response based at least in part on the value for the second complex basis function.

3. The system of claim 2, wherein the digital pre-distortion circuit is further programmed to before determining the value for the first complex basis function, translate the first complex basis function by the carrier frequency.

4. The system of claim 2, wherein the digital pre-distortion circuit is further programmed to:

receive a complex feedback signal based at least in part on an output of the power amplifier;

compare the complex feedback signal to the pre-distorted signal; and

determine a coefficient for the first FIR filter based at least in part on the compare of the complex feedback signal to the pre-distorted signal.

5. The system of claim 2, wherein the digital pre-distortion circuit is further programmed to:

receive a complex feedback signal based at least in part on an output of the power amplifier;

generate a feedback matrix based at least in part on the complex feedback signal;

generate an I^th harmonic frequency zone basis vector comprising a first plurality of complex basis function values, the first plurality of complex basis function values comprising the value for the first complex basis function;

generate a Jth harmonic frequency zone basis vector comprising a second plurality of complex basis function values, the second plurality of complex basis function values comprising the value for the second complex basis function;

generate a basis matrix comprising the first frequency zone basis vector and the second frequency zone basis vector;

compare the basis matrix to the feedback matrix; and

determine a coefficient for the first FIR filter based at least in part on the compare of the basis matrix to the feedback matrix.

6. The system of claim 2, wherein the value for the first complex basis function is based at least in part on a first value of the complex baseband signal at a first time, wherein the digital pre-distortion circuit is further programmed to:

apply a first tap of the first FIR filter to the first value of the complex baseband signal at the first time; and

apply a second tap of the first FIR filter to a second value of the complex baseband signal at a second time that is before the first time.

7. The system of claim 1, wherein the digital pre-distortion circuit is further programmed to:

determine a first magnitude of the complex baseband signal at a first time;

for the I^th harmonic frequency zone;

generate an I^th harmonic frequency zone exponent based at least in part on an the N^th order distortion of the power amplifier;

generate an I^th harmonic frequency zone multiplier for the first time based at least in part on the I^th harmonic frequency zone exponent;

select a first look up table (LUT) value from a first tap LUT of the I^th harmonic frequency zone based at least in part on the first magnitude of the complex baseband signal;

generate a first tap LUT product for the I^th harmonic frequency zone based at least in part on the first LUT value and the I^th harmonic frequency zone multiplier for the first time; and

generate an I^th harmonic frequency zone output based at least in part on the first tap LUT product for the I^th harmonic frequency zone and an I^th harmonic frequency zone carrier component;

for the J^th harmonic frequency zone;

generate a J^th harmonic frequency zone exponent based at least in part on the Nth order distortion of the power amplifier;

generate a J^th harmonic frequency zone multiplier based at least in part on the J^th harmonic frequency zone exponent;

select a second LUT value from a first tap LUT of the J^th harmonic frequency zone based at least in part on the first magnitude of the complex baseband signal;

generate a first tap LUT product for the J^th harmonic frequency zone based at least in part on the second LUT value and the J^th harmonic frequency zone multiplier; and

generate a J^th harmonic frequency zone output based at least in part on the first tap LUT product for the J^th harmonic frequency zone and a J^th harmonic frequency zone carrier component.

8. The system of claim 7, wherein the generate of the I^th harmonic frequency zone multiplier for the first time comprises raising a first value of the complex baseband signal at the first time to the I^th harmonic frequency zone exponent.

9. The system of claim 7, wherein the generate of the first tap LUT product for the I^th harmonic frequency zone comprises multiplying the first LUT value and the I^th harmonic frequency zone multiplier.

10. The system of claim 7, wherein the digital pre-distortion circuit is further programmed to, for the I^th harmonic frequency zone:

determine a second magnitude of the complex baseband signal at a second time before the first time;

generate an I^th harmonic frequency zone multiplier for the second time based at least in part on the I^th harmonic frequency zone exponent and a second value of the complex baseband signal at the second time;

select a third look up table (LUT) value from a second tap LUT of the I^th harmonic frequency zone based at least in part on the second magnitude of the complex baseband signal; and

generate a second tap LUT product for the I^th harmonic frequency zone based at least in part on the third LUT value and the I^th harmonic frequency zone multiplier for the second time, wherein the I^th harmonic frequency zone output is also based at least on part on the second tap LUT product.

11. The system of claim 7, wherein the digital pre-distortion circuit is further programmed to:

receive a complex feedback signal based at least in part on an output of the power amplifier;

compare the complex feedback signal to the pre-distorted signal; and

populate the first tap LUT based at least in part on the comparing.

12. The system of claim 1, wherein the digital pre-distortion circuit is further programmed to:

generate an I^th harmonic frequency zone exponent for the I^th harmonic frequency zone based at least in part on the N^th order distortion of the power amplifier;

generate a I^th harmonic frequency zone multiplier based at least in part on the I^th harmonic frequency zone exponent;

select a LUT value from a first tap LUT of the I^th harmonic frequency zone based at least in part on a first magnitude of the complex baseband signal at a first time;

generate a first tap LUT product for the I^th harmonic frequency zone based at least in part on the LUT value and the I^th harmonic frequency zone multiplier; and

generate an I^th harmonic t frequency zone output based at least in part on the first tap LUT product for the I^th harmonic frequency zone and an N^th harmonic frequency zone carrier component;

determine a value for a first complex basis function for the N^th order distortion of the power amplifier at a J^th harmonic frequency zone, wherein the first complex basis function is based at least in part on the complex baseband signal; and

apply a first finite impulse response (FIR) filter to generate a first FIR response based at least in part on the value for the first complex basis function.

13. The system of claim 1, wherein the digital pre-distortion circuit is further programmed to up-sample the complex baseband signal to generate an up-sampled complex baseband signal, wherein the applying of the first correction and the applying of the second correction is based at least in part on the up-sampled baseband signal.

14. The system of claim 1, wherein the digital pre-distortion circuit is further programmed to:

up-sample the complex baseband signal to an up-sampled frequency generate an up-sampled complex baseband signal, wherein the pre-distorted signal is at the up-sampled frequency;

determine a real component of the pre-distorted signal; and

apply a Hilbert transform to the real component of the pre-distorted signal.

15. The system of claim 1, wherein the generating of the pre-distorted signal further comprises:

up-sampling the complex baseband signal to generate an up-sampled complex baseband signal, wherein the applying the first correction and the applying the second correction are based at least in part on the up-sampled complex baseband signal; and

applying to the complex baseband signal a third correction for a 1^st order term of the power amplifier at a K^th harmonic frequency zone centered at the carrier frequency based at least in part on the complex baseband signal.

16. The system of claim 1, wherein the J^th harmonic frequency zone is the highest frequency zone corrected by the digital pre-distortion circuit, and wherein N is greater than J.

17. A method comprising:

receiving a complex baseband signal; and

generating a pre-distorted signal, wherein the generating comprises;

applying to the complex baseband signal a first correction for an N^th order distortion of a power amplifier at an I^th harmonic frequency zone centered at about an I^th harmonic of a carrier frequency; and

applying to the complex baseband signal a second correction for the N^th order distortion at a J^th harmonic frequency zone centered at about a J^th harmonic of the carrier frequency different than the I^th harmonic of the carrier frequency.

18. The method of claim 17, further comprising:

determining a value for a first complex basis function for the N^th order distortion at the I^th harmonic frequency zone based at least in part on the complex baseband signal;

determining a value for a second complex basis function for the N^th order distortion at the I^th harmonic frequency zone based at least in part on the complex baseband signal;

applying a first finite impulse response (FIR) filter to generate a first FIR response based at least in part on the value for the first complex basis function; and

applying a second FIR filter to generate a second FIR response based at least in part on the value for the second complex basis function.

19. The method of claim 17, further comprising:

determining a first magnitude of the complex baseband signal at a first time;

for the I^th harmonic frequency zone;

generating an I^th harmonic frequency zone exponent based at least in part on an the N^th order distortion of the power amplifier;

generating an I^th harmonic frequency zone multiplier for the first time based at least in part on the I^th harmonic frequency zone exponent;

selecting a first look up table (LUT) value from a first tap LUT of the I^th harmonic frequency zone based at least in part on the first magnitude of the complex baseband signal;

generating a first tap LUT product for the I^th harmonic frequency zone based at least in part on the first LUT value and the I^th harmonic frequency zone multiplier for the first time; and

generating an I^th harmonic frequency zone output based at least in part on the first tap LUT product for the I^th harmonic frequency zone and an I^th harmonic frequency zone carrier component;

for the J^th harmonic frequency zone;

generating a J^th harmonic frequency zone exponent based at least in part on the N^th order distortion of the power amplifier generating a J^th harmonic frequency zone multiplier based at least in part on the Jth harmonic frequency zone exponent;

selecting a second LUT value from a first tap LUT of the J^th harmonic frequency zone based at least in part on the first magnitude of the complex baseband signal;

generating a first tap LUT product for the J^th harmonic frequency zone based at least in part on the second LUT value and the J^th harmonic frequency zone multiplier; and

generating a J^th harmonic frequency zone output based at least in part on the first tap LUT product for the J^th harmonic frequency zone and a JP harmonic frequency zone carrier component.

20. The method of claim 17, further comprising:

generating an I^th harmonic frequency zone exponent for the I^th harmonic frequency zone based at least in part on the N^th order distortion of the power amplifier;

generating a I^th harmonic frequency zone multiplier based at least in part on the I^th harmonic frequency zone exponent;

selecting a LUT value from a first tap LUT of the I^th harmonic frequency zone based at least in part on a first magnitude of the complex baseband signal at a first time;

generating a first tap LUT product for the I^th harmonic frequency zone based at least in part on the LUT value and the I^th harmonic frequency zone multiplier; and

generating an I^th harmonic t frequency zone output based at least in part on the first tap LUT product for the I^th harmonic frequency zone and an I^th harmonic frequency zone carrier component;

determining a value for a first complex basis function for the N^th order distortion of the power amplifier at a J^th harmonic frequency zone, wherein the first complex basis function is based at least in part on the complex baseband signal; and

applying a first finite impulse response (FIR) filter to generate a first FIR response based at least in part on the value for the first complex basis function.