LINEARIZATION OF HETEROGENEOUS POWER AMPLIFIER SYSTEMS

• US 20140340155A1
• Filed: 03/15/2013
• Published: 11/20/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: GatesAir Incorporated (Groupe Sipromad SA)
• Original Assignee: HBC Solutions Incorporated (AEG Holdings, Inc.)
• Inventors: Borodulin, Dmitri, Berndsen, Kevin J.
• Granted Patent: US 8,952,754 B2
• Time in Patent Office: Days
• US Class Current: 330/291
• CPC Class Codes: H03F 1/0277 Selecting one or more amplifiers from a plurality of amplifiers
• 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 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• 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 1/3258 based on polynomial terms
• CPC Class Codes: H03F 1/3282 Acting on the phase and the amplitude of the input signal
• CPC Class Codes: H03F 2200/204 A hybrid coupler being used at the output of an amplifier circuit
• CPC Class Codes: H03F 2200/207 A hybrid coupler being used as power measuring circuit at the output of an amplifier circuit
• CPC Class Codes: H03F 2200/451 the amplifier being a radio frequency amplifier
• 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 2201/3227 Adaptive predistortion based on amplitude, envelope or power level feedback from the output of the main amplifier
• CPC Class Codes: H03F 2203/21142 Output signals of a plurality of power amplifiers are parallel combined to a common output
• CPC Class Codes: H03F 3/189 High-frequency amplifiers, e.g. radio frequency amplifiers
• CPC Class Codes: H03F 3/19 with semiconductor devices only
• CPC Class Codes: H03F 3/211 using a combination of several amplifiers H03F3/60 takes precedence
• CPC Class Codes: H03F 3/245 with semiconductor devices only
• CPC Class Codes: H03F 3/72 Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal
• CPC Class Codes: H04L 27/206 using a pair of orthogonal carriers, e.g. quadrature carriers
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

Systems and methods are provided for adaptive linearization of an amplifier system having a plurality of heterogeneous amplifier paths. An amplifier system includes a plurality of amplifier paths, each configured to provide an amplified output signal from an input signal, and a signal combiner configured to combine the amplified output signals from the plurality of amplifier paths to provide a system output, such that the system output is a non-linear function of the amplified output signals. A monitoring system is configured to sample the system output and normalize the sampled output to a signal level associated with the input signal. A signal processing component is configured to characterize the amplifier paths via an iterative adaptive linearization process, such that the system output is linear with respect to the input signal.

Claims

1. A method for linearizing an amplifier system having a plurality of heterogeneous amplifier paths, the method comprising:

selecting a first amplifier path of the plurality of heterogeneous amplifier paths;

providing an input signal to the amplifier system;

sampling an output of the amplifier system and an output of a predistorter on the first amplifier path to produce a set of matched pairs of predistorted input values, each predistorted via a current predistortion function of the first amplifier path, and corresponding system outputs;

subtracting, for each of the matched pairs, an expected contribution of each amplifier path of the plurality of heterogeneous amplifier paths that is not the first amplifier path from the corresponding system output to produce a set of modified data points comprising the predistorted input values and corresponding modified system outputs; and

determining a new predistortion function for the first amplifier path from the set of modified data points.

2. The method of claim 1, further comprising determining an initial predistortion function for the first amplifier path, wherein determining an initial predistortion function for the first amplifier path comprises:

muting each of the plurality of amplifier paths other than the first amplifier path;

providing a reference signal to the amplifier system;

sampling the output of the amplifier system to produce a set of input values and corresponding system outputs; and

determining the initial predistortion function for the first amplifier path from the set of input values and corresponding system outputs.

3. The method of claim 1, further comprising applying a linear inverse transformation on the modified system outputs, the linear inverse transform representing a relationship between a given input value to the first amplifier path and a corresponding ideal output from that path.

4. The method of claim 1, wherein determining the new predistortion function for the first amplifier path comprises fitting a curve to the set of modified data points as a complex-valued spline.

5. The method of claim 1, further comprising:

selecting a second amplifier path of the plurality of heterogeneous amplifier paths;

sampling the output of the amplifier system and an output of a predistorter on the second amplifier path to produce a set of matched pairs of input values, each predistorted via a current predistortion function of the second amplifier path, and corresponding system outputs;

subtracting, for each of the matched pairs, an expected contribution of each amplifier path of the plurality of heterogeneous amplifier paths that is not the second amplifier path from the corresponding system output to produce a set of modified data points comprising the predistorted input values and corresponding modified system outputs; and

determining a new predistortion function for the second amplifier path from the set of modified data points.

6. The method of claim 5, further comprising iteratively repeating the following steps until a termination condition is achieved:

selecting a next amplifier path of the plurality of heterogeneous amplifier paths;

sampling the output of the amplifier system and the output of a predistorter on the selected amplifier path to produce a set of matched pairs of input values, each predistorted via the current predistortion function of the selected amplifier path, and corresponding system outputs;

subtracting, for each of the matched pairs, the expected contribution of each amplifier path of the plurality of heterogeneous amplifier paths that is not the selected amplifier path from the corresponding system output to produce a set of modified data points comprising the predistorted input values and corresponding modified system outputs; and

determining a new predistortion function for the selected amplifier path from the set of modified data points.

7. The method of claim 6, the iteratively repeated steps further comprising calculating an error metric for the new predistortion function, the termination condition comprising calculation of an error metric that meets a threshold value.

8. The method of claim 7, wherein the error metric comprises a sum-squared difference between an baseband input amplitude provided to the amplifier system and a corresponding output value, normalized to match a signal level associated with the baseband input signal.

9. The method of claim 1, wherein the predistortion function represents a range that is a proper subset of the range of available input values for the system.

10. The method of claim 1, further comprising calculating the expected contribution of each amplifier path of the plurality of heterogeneous amplifier paths that is not the first amplifier path as the value of a non-linear function associated with the amplifier path evaluated at the input value.

11. An amplifier system comprising:

a plurality of amplifier paths each configured to provide an amplified output signal from an input signal;

a signal combiner configured to combine the amplified output signals from the plurality of amplifier paths to provide a system output, such that the system output is a non-linear function of the amplified output signals;

a monitoring system configured to sample the system output and normalize the sampled output to a signal level associated with the input signal; and

a signal processing component configured to characterize the amplifier paths via an iterative adaptive linearization process, such that the system output is linear with respect to the input signal.

12. The amplifier system of claim 11, each of the plurality of amplifier paths comprising a non-linear transform applied to the input signal to provide a transformed input, and a predistortion component configured to apply a predistortion to the transformed input reflecting the characterization of the output path at the signal processing component.

13. The amplifier system of claim 12, wherein the monitoring component is further configured to sample an output of the predistortion component on each amplifier path, the signal processing component characterizing the amplifier paths according to at least the outputs of the predistortion components and the system output.

14. The amplifier system of claim 13, the signal processing component being configured to iteratively select an amplifier path of the plurality of amplifier paths, calculate an expected contribution of each amplifier path other than the selected amplifier path, subtract the calculated expected contributions from the system output to provide a modified system output, and fit a curve to a set of values for the output of the predistorter for the selected path and the corresponding modified system outputs.

15. The amplifier system of claim 14, wherein the signal processing component calculates the expected contribution of each amplifier path other than the selected amplifier path by evaluating the non-linear transform associated with the amplifier path at a value of the input signal corresponding to the output of the predistorter for the selected path.

16. The amplifier system of claim 13, the signal processing component being configured to iteratively select an amplifier path of the plurality of amplifier paths, calculate an expected contribution of each amplifier path other than the selected amplifier path, subtract the calculated expected contributions from the system output to provide a modified system output, apply an inverse linear transform, based on the non-linear transform associated with the selected amplifier path to provide a set of transformed output values, and fit a curve to a set of values for the output of the predistorter for the selected path and the corresponding transformed output values.

17. An amplifier system comprising:

a main amplifier path having an associated main predistortion component to apply a predistortion function to an input signal;

an auxiliary amplifier path having an associated auxiliary predistortion component to apply a predistortion function to the input signal;

a signal combiner configured to combine respective outputs from the main and auxiliary amplifier paths to provide a system output, such that the system output is a non-linear function of the outputs;

a monitoring system configured to sample the system output and an output of each of the auxiliary predistortion component and the main predistortion component; and

a signal processing component configured to select the auxiliary amplifier path, calculate an expected contribution of the main amplifier path as an expected input to the main predistortion component for a given amplitude of the input signal, subtract the calculated expected contribution from the system output to provide a modified system output, fit a curve to a set of values for the output of the auxiliary predistortion component and the corresponding modified system outputs, and update the auxiliary predistortion component with a new predistortion function derived from the curve fitting.

18. The amplifier system of claim 17, the signal processing component being configured to select the main amplifier path, calculate an expected contribution of the auxiliary amplifier path as an expected input to the auxiliary predistortion component for a given amplitude of the input signal, subtract the calculated expected contribution from the system output to provide a modified system output, transform the modified system output according to an inverse linear transform derived from a non-linear transform associated with the main amplifier path to provide a transformed system output, fit a curve to a set of values for the output of the auxiliary predistortion component and the corresponding transformed system output, and update the main predistortion component with a new predistortion function derived from the curve fitting.

19. The amplifier system of claim 17, each of the main and auxiliary amplifier paths comprising respective non-linear transforms applied to the input signal to provide respective transformed input signal to respective sets of at least one amplifier associated with the amplifier path.

20. The amplifier system of claim 17, wherein the signal combiner is a quadrature combiner and the main amplifier path comprises at least two amplifiers, with the outputs of first and second amplifiers associated with the main amplifier path provided, respectively, to through and coupled ports of the quadrature combiner, and an output of the auxiliary amplifier path provided to an isolation port of the quadrature combiner.