# US 11,115,067 B2 · Multi-band linearization system

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- Number: US 11,115,067 B2
- Document ID: US11115067B2
- Status: Granted
- Kind: B2
- Application number: 16/004,713
- Filed: 2018-06-11
- Published: 2019-08-22
- Granted: 2021-09-07
- Earliest claimed: 2017-06-09
- Assignees: NanoSemi, Inc.
- Applicants: NanoSemi, Inc.
- Inventors: Kevin Chuang; Alexandre Megretski; Yan Li; Helen H. Kim
- Web page: https://patentgrep.com/patent/US11115067B2

## CPC

- H04B 1/0475: {with means for limiting noise, interference or distortion (H04B1/0483 takes precedence)}
- H04B 2001/0425: {with linearisation using predistortion}
- H04B: TRANSMISSION

## Abstract

Disclosed are implementations, including a method for digital predistortion of multiband signals that includes receiving an input signal comprising multiple signal portions in different frequency bands, the input signal configured to be processed by a transmit chain, of a power amplification system, comprising at least a power amplifier that produces output with non-linear distortions, with the non-linear distortions of the transmit chain being represented using a set of basis functions derived according to a single-band model of the non-linear distortions. The method further includes performing digital predistortion on signal components derived from the multiple signal portions of the input signal using a reduced set of the basis functions that excludes at least some basis functions for at least some cross-terms resulting from a full expansion of the single-band model applied to the multiple signal portions, to produce a digital predistorted signal provided to the transmit chain.

## Claims

### Claim 1

A method for digital predistortion of multiband signals, the method comprising:
receiving an input signal comprising multiple signal portions in different frequency bands, the input signal configured to be processed by a transmit chain of a power amplification system with the transmit chain comprising at least a power amplifier that produces output with non-linear distortions, wherein the non-linear distortions of the transmit chain are represented using a set of basis functions derived according to a single-band model of the non-linear distortions; and
performing digital predistortion on signal components derived from the multiple signal portions of the input signal using a reduced set of the basis functions that excludes at least some basis functions for at least some cross-terms resulting from a full expansion of the single-band model of the non-linear distortions applied to the multiple signal portions, to produce a digital predistorted signal provided to the transmit chain;
wherein performing the digital predistortion comprises computing digital predistortion coefficients to weigh the reduced set of basis functions, including deriving a first group of coefficients for a first group of the basis function terms operating on input values of the signal components, a second group of coefficients for a second group of basis function terms operating on normalized input values of the signal components, and a third group of coefficients for a third group of basis function terms operating on input values of combinations of the signal components.

### Claim 2 (depends on 1)

The method of claim 1, wherein performing the digital predistortion on the signal components derived from the multiple signal portions of the input signal using the reduced set of the basis functions comprises:
performing the digital predistortion on the signal components using a sampling rate corresponding to a sampling bandwidth that is larger than any individual one of the different frequency bands for the multiple signal portions, but smaller than a total input bandwidth for the input signal comprising the multiple signal portions.

### Claim 3 (depends on 1)

The method of claim 1, wherein the excluded at least some resultant basis functions comprise cross-terms basis functions for two or more of the multiple signal portions in the different frequency bands.

### Claim 4 (depends on 3)

The method of claim 3, wherein the excluded at least some basis functions include the cross-terms basis functions for the two or more of the multiple signal portions that are located at frequency locations outside a pre-determined frequency reference window.

### Claim 5 (depends on 3)

The method of claim 3, wherein the excluded at least some basis functions include the cross-terms basis functions for the two or more of the multiple signal portions that are located at frequency locations outside a pre-determined frequency reference window, and have relative energy levels below a pre-determined energy threshold.

### Claim 6 (depends on 1)

The method of claim 1, wherein the signal components comprise one or more of: individual separated parts of the multiple signal portions, individual normalized parts of the multiple signal portions, or cross-term combinations of one or more of the individual parts of the multiple signal portions.

### Claim 7 (depends on 6)

The method of claim 6, further comprising:
separating the multiple signal portions into the individual separated parts of the multiple signal portions.

### Claim 8 (depends on 7)

The method of claim 7, wherein separating the multiple signal portions into the individual separated parts comprises:
applying one or more bandpass filters to the input signal to produce the individual separated parts.

### Claim 9 (depends on 6)

The method of claim 6, further comprising:
computing the individual normalized parts of the multiple signal portions according to:
w
j
=
x
j
⁢
1
(
∑
k
=
1
n
⁢

x
k

2
)
p
wherein xj is one of n individual parts of the multiple signal portions of the input signal, and wherein p includes a fractional exponent selected to yield good performance for an output of the transmit chain resulting from the produced digital predistorted signal.

### Claim 10 (depends on 1)

The method of claim 1, further comprising:
applying the input values of the signal components to the respective first group of the basis function terms, weighed by the first group of digital predistortion coefficients, to produce first resultant signals;
applying the normalized input values of the signal components to the respective second group of basis functions, weighed by the second group of digital predistortion coefficients, to produce second resultant signals;
applying the input values of the combinations of the signal components to the respective third group of basis functions, weighed by the third group of digital predistortion coefficients, to produce third resultant signals; and
combining the first resultant signals, the second resultant signals, and the third resultant signals to produce the digital predistorted signal.

### Claim 11 (depends on 1)

The method of claim 1, wherein computing the digital predistortion coefficients comprises:
periodically computing the digital predistortion coefficients used to weigh the reduced set of basis function terms.

### Claim 12 (depends on 11)

The method of claim 11, wherein periodically computing the digital predistortion coefficients comprises:
periodically computing the digital predistortion coefficients that result in a minimization of a difference between amplified values of one or more instances of the signal components, and observed output signals of the transmit chain resulting from inputting into the transmit chain a resultant signal produced by weighing the reduced set of the basis functions by the computed digital predistortion coefficients and applying to the weighed reduced set of the basis functions the one or more instances of the signal components.

### Claim 13 (depends on 1)

The method of claim 1, wherein performing digital predistortion on the signals components derived from the multiple signal portions of the input signal comprises:
excluding basis functions for cross-terms outside a pre-determined bandwidth, and retaining individual separated parts basis functions outside the pre-determined bandwidth, the individual separated parts basis function computed from individual parts of the multiple signal portions that are each located in a single respective frequency band from the different frequency bands.

### Claim 14

A system for digital predistortion of multiband signals, the system comprising:
a power amplification system comprising a transmit chain including at least a power amplifier that produces output with non-linear distortions, wherein the non-linear distortions of the transmit chain are represented using a set of basis functions derived
according to a single-band model of the non-linear distortions; and a controller to perform digital predistortion on signal components derived from multiple signal portions of an input signal using a reduced set of the basis functions that excludes at least some basis functions for at least some cross-terms resulting from a full expansion of the single-band model of the non-linear distortions applied to the multiple signal portions, to produce a digital predistorted signal provided to the transmit chain;
wherein the controller configured to perform the digital predistortion is configured to compute digital predistortion coefficients to weight the reduced set of basis functions, including to derive a first group of coefficients for a first group of the basis function terms operating on input values of the signal components, a second group of coefficients for a second group of basis function terms operating on normalized input values of the signal components, and a third group of coefficients for a third group of basis function terms operating on input values of combinations of the signal components.

### Claim 15 (depends on 14)

The system of claim 14, wherein the excluded at least some resultant basis functions comprise cross-terms basis functions for two or more of the multiple signal portions in the different frequency bands.

### Claim 16 (depends on 15)

The system of claim 15, wherein the excluded at least some basis functions include the cross-terms basis functions for the two or more of the multiple signal portions that are located at frequency locations outside a pre-determined frequency reference window.

### Claim 17 (depends on 14)

The system of claim 14, wherein the signal components comprise one or more of: individual separated parts of the multiple signal portions, individual normalized parts of the multiple signal portions, or cross-term combinations of one or more of the individual parts of the multiple signal portions.

### Claim 18 (depends on 17)

The system of claim 17, wherein the controller is further configured to:
compute the individual normalized parts of the multiple signal portions according to:
w
j
=
x
j
⁢
1
(
∑
k
=
1
n
⁢

x
k

2
)
p
wherein xj is one of n individual parts of the multiple signal portions of the input signal, and wherein p includes a fractional exponent selected to yield good performance for an output of the transmit chain resulting from the produced digital predistorted signal.

### Claim 19 (depends on 14)

The system of claim 14, wherein the controller configured to perform the digital predistortion on the signal components derived from the multiple signal portions of the input signal using the reduced set of the basis functions is configured to:
perform the digital predistortion on the signal components using a sampling rate corresponding to a sampling bandwidth that is larger than any individual one of the different frequency bands for the multiple signal portions, but smaller than a total input bandwidth for the input signal comprising the multiple signal portions.

### Claim 20 (depends on 14)

The system of claim 14, wherein the controller configured to perform digital predistortion on the signals components derived from the multiple signal portions of the input signal is configured to:
exclude basis functions for cross-terms outside a pre-determined bandwidth, and retaining individual separated parts basis functions outside the pre-determined bandwidth, the individual separated parts basis function computed from individual parts of the multiple signal portions that are each located in a single respective frequency band from the different frequency bands.

### Claim 21

A design structure encoded on a non-transitory machine-readable medium,
said design structure comprising elements that to be processed in a computer-aided design system, to generate a machine-executable representation of a multiband predistorter, the multiband predistorter comprising: a power amplification circuit comprising a transmit chain including at least a power amplifier that produces output with non-linear distortions, wherein the non-linear distortions of the transmit chain are represented using a set of basis functions derived according to a single-band model of the non-linear distortions; and a control circuit to perform digital predistortion on signal components derived from multiple signal portions of an input signal using a reduced set of the basis functions that excludes at least some basis functions for at least some cross-terms resulting from a full expansion of the single-band model of the non-linear distortions applied to the multiple signal portions, to produce a digital predistorted signal provided to the transmit chain;
wherein the control circuit configured to perform the digital predistortion is configured to compute digital predistortion coefficients to weight the reduced set of basis functions, including to derive a first group of coefficients for a first group of the basis function terms operating on input values of the signal components, a second group of coefficients for a second group of basis function terms operating on normalized input values of the signal components, and a third group of coefficients for a third group of basis function terms operating on input values of combinations of the signal components.

### Claim 22

A non-transitory computer readable media programmed with instructions, executable on a processor, to:
receive an input signal comprising multiple signal portions in different frequency bands, the input signal configured to be processed by a transmit chain of a power amplification system with the transmit chain comprising at least a power amplifier that produces output with non-linear distortions, wherein the non-linear distortions of the transmit chain are represented using a set of basis functions derived according to a single-band model of the non-linear distortions; and
perform digital predistortion on signal components derived from the multiple signal portions of the input signal using a reduced set of the basis functions that excludes at least some basis functions for at least some cross-terms resulting from a full expansion of the single-band model of the non-linear distortions applied to the multiple signal portions, to produce a digital predistorted signal provided to the transmit chain;
wherein the instructions to perform the digital predistortion include one or more instructions to compute digital predistortion coefficients to weight the reduced set of basis functions, including to derive a first group of coefficients for a first group of the basis function terms operating on input values of the signal components, a second group of coefficients for a second group of basis function terms operating on normalized input values of the signal components, and a third group of coefficients for a third group of basis function terms operating on input values of combinations of the signal components.

### Claim 23

A method for digital predistortion of multiband signals, the method comprising:
receiving an input signal comprising multiple signal portions in different frequency bands, the input signal configured to be processed by a transmit chain of a power amplification system with the transmit chain comprising at least a power amplifier that produces output with non-linear distortions, wherein the non-linear distortions of the transmit chain are represented using a set of basis functions derived according to a single-band model of the non-linear distortions; and
performing digital predistortion on signal components derived from the multiple signal portions of the input signal using a reduced set of the basis functions that excludes at least some basis functions for at least some cross-terms resulting from a full expansion of the single-band model of the non-linear distortions applied to the multiple signal portions, to produce a digital predistorted signal provided to the transmit chain;
wherein the signal components comprise individual normalized parts of the multiple signal portions;
and wherein the method further includes computing the individual normalized parts of the multiple signal portions according to:
w
j
=
x
j
⁢
1
(
∑
k
=
1
n
⁢

x
k

2
)
p
wherein xj is one of n individual parts of the multiple signal portions of the input signal, and wherein p includes a fractional exponent selected to yield good performance for an output of the transmit chain resulting from the produced digital predistorted signal.

### Claim 24 (depends on 23)

The method of claim 23, wherein performing the digital predistortion on the signal components derived from the multiple signal portions of the input signal using the reduced set of the basis functions comprises:
performing the digital predistortion on the signal components using a sampling rate corresponding to a sampling bandwidth that is larger than any individual one of the different frequency bands for the multiple signal portions, but smaller than a total input bandwidth for the input signal comprising the multiple signal portions.

### Claim 25 (depends on 23)

The method of claim 23, wherein the excluded at least some resultant basis functions comprise cross-terms basis functions for two or more of the multiple signal portions in the different frequency bands.

### Claim 26 (depends on 25)

The method of claim 25, wherein the excluded at least some basis functions include the cross-terms basis functions for the two or more of the multiple signal portions that are located at frequency locations outside a pre-determined frequency reference window, and have relative energy levels below a pre-determined energy threshold.

### Claim 27 (depends on 23)

The method of claim 23, wherein the signal components further comprise one or more of: individual separated parts of the multiple signal portions, or cross-term combinations of one or more of the individual parts of the multiple signal portions, and wherein the method further comprises:
separating the multiple signal portions into the individual separated parts of the multiple signal portions, including applying one or more bandpass filters to the input signal to produce the individual separated parts.

### Claim 28 (depends on 23)

The method of claim 23, wherein computing the digital predistortion coefficients comprises:
periodically computing the digital predistortion coefficients used to weigh the reduced set of basis function terms.

### Claim 29 (depends on 23)

The method of claim 23, wherein performing digital predistortion on the signals components derived from the multiple signal portions of the input signal comprises:
excluding basis functions for cross-terms outside a pre-determined bandwidth, and retaining individual separated parts basis functions outside the pre-determined bandwidth, the individual separated parts basis function computed from individual parts of the multiple signal portions that are each located in a single respective frequency band from the different frequency bands.

### Claim 30

A system for digital predistortion of multiband signals, the system comprising:
a power amplification system comprising a transmit chain including at least a power amplifier that produces output with non-linear distortions, wherein the non-linear distortions of the transmit chain are represented using a set of basis functions derived according to a single-band model of the non-linear distortions; and a controller to perform digital predistortion on signal components derived from multiple signal portions of an input signal using a reduced set of the basis functions that excludes at least some basis functions for at least some cross-terms resulting from a full expansion of the single-band model of the non-linear distortions applied to the multiple signal portions, to produce a digital predistorted signal provided to the transmit chain;
wherein the signal components comprise individual normalized parts of the multiple signal portions;
and wherein the controller is further configured to compute the individual normalized parts of the multiple signal portions according to:
w
j
=
x
j
⁢
1
(
∑
k
=
1
n
⁢

x
k

2
)
p
wherein xj is one of n individual parts of the multiple signal portions of the input signal, and wherein p includes a fractional exponent selected to yield good performance for an output of the transmit chain resulting from the produced digital predistorted signal.

### Claim 31 (depends on 30)

The system of claim 30, wherein the excluded at least some resultant basis functions comprise cross-terms basis functions for two or more of the multiple signal portions in the different frequency bands.

### Claim 32 (depends on 31)

The system of claim 31, wherein the excluded at least some basis functions include the cross-terms basis functions for the two or more of the multiple signal portions that are located at frequency locations outside a pre-determined frequency reference window, and have relative energy levels below a pre-determined energy threshold.

### Claim 33 (depends on 30)

The system of claim 30, wherein the controller configured to perform the digital predistortion on the signal components derived from the multiple signal portions of the input signal using the reduced set of the basis functions is configured to:
perform the digital predistortion on the signal components using a sampling rate corresponding to a sampling bandwidth that is larger than any individual one of the different frequency bands for the multiple signal portions, but smaller than a total input bandwidth for the input signal comprising the multiple signal portions.

### Claim 34 (depends on 30)

The system of claim 30, wherein the signal components further comprise one or more of: individual separated parts of the multiple signal portions, or cross-term combinations of one or more of the individual parts of the multiple signal portions, and wherein the controller is further configured to:
separate the multiple signal portions into the individual separated parts of the multiple signal portions, including to apply one or more bandpass filters to the input signal to produce the individual separated parts.

### Claim 35 (depends on 30)

The system of claim 30, wherein the controller configured to perform digital predistortion on the signals components derived from the multiple signal portions of the input signal is configured to:
exclude basis functions for cross-terms outside a pre-determined bandwidth, and retaining individual separated parts basis functions outside the pre-determined bandwidth, the individual separated parts basis function computed from individual parts of the multiple signal portions that are each located in a single respective frequency band from the different frequency bands.