Amplifier measurement and modeling processes for use in generating predistortion parameters
First Claim
1. A method of generating an initial set of compensation parameters for use within a compensation circuit that predistorts an input transmission signal to a wideband amplifier to compensate for nonlinearities in an amplification process, the method comprising:
- applying stimulation signals to the amplifier while recording observation data that represents a resulting output of the amplifier;
evaluating the observation data to measure selected characteristics of the amplifier;
constructing a non-linear model of the amplifier which incorporates the selected characteristics;
adaptively adjusting the amplifier model to improve an accuracy of the model; and
using the adjusted amplifier model to generate the initial set of compensation parameters.
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Abstract
A wideband predistortion system compensates for a nonlinear amplifier'"'"'s frequency and time dependent AM-AM and AM-PM distortion characteristics. The system comprises a data structure in which each element stores a set of compensation parameters (preferably including FIR filter coefficients) for predistorting the wideband input transmission signal. The parameter sets are preferably indexed within the data structure according to multiple signal characteristics, such as instantaneous amplitude and integrated signal envelope, each of which corresponds to a respective dimension of the data structure. To predistort the input transmission signal, an addressing circuit digitally generates a set of data structure indices from the input transmission signal, and the indexed set of compensation parameters is loaded into a compensation circuit which digitally predistorts the input transmission signal. This process of loading new compensation parameters into the compensation circuit is preferably repeated every sample instant, so that the predistortion function varies from sample-to-sample. The sets of compensation parameters are generated periodically and written to the data structure by an adaptive processing component that performs a non-real-time analysis of amplifier input and output signals. The adaptive processing component also implements various system identification processes for measuring the characteristics of the power amplifier and generating initial sets of filter coefficients. In an antenna array embodiment, a single adaptive processing component generates the compensation parameters sets for each of multiple amplification chains on a time-shared basis. In an embodiment in which the amplification chain includes multiple nonlinear amplifiers that can be individually controlled (e.g., turned ON and OFF) to conserve power, the data structure separately stores compensation parameter sets for each operating state of the amplification chain.
73 Citations
77 Claims
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1. A method of generating an initial set of compensation parameters for use within a compensation circuit that predistorts an input transmission signal to a wideband amplifier to compensate for nonlinearities in an amplification process, the method comprising:
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applying stimulation signals to the amplifier while recording observation data that represents a resulting output of the amplifier;
evaluating the observation data to measure selected characteristics of the amplifier;
constructing a non-linear model of the amplifier which incorporates the selected characteristics;
adaptively adjusting the amplifier model to improve an accuracy of the model; and
using the adjusted amplifier model to generate the initial set of compensation parameters. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A method for modeling a wideband amplifier, comprising:
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(a) applying stimulation signals to the amplifier to measure characteristics of the amplifier;
(b) using the characteristics measured in (a) to generate a non-linear model of the amplifier;
(c) applying an input signal to the model and to the amplifier while monitoring a difference between respective outputs thereof, and adaptively adjusting parameters of the model until an error floor in the difference is substantially reached; and
(d) increasing a level of complexity of the model and then repeating (c). - View Dependent Claims (31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46)
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47. A method of generating a model of a wideband amplifier, comprising:
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applying narrowband stimulation signals to the amplifier over a plurality of amplitude levels and a plurality of center frequencies, and using resulting amplifier output data to compute amplitude-dependent and frequency-dependent variations in at least the gain and phase rotation introduced by the amplifier;
applying a wideband stimulation signal to the amplifier, and using resulting output data to compute bulk estimates of at least the gain, phase rotation and delay introduced by the amplifier;
generating a data structure which contains multiple sets of finite impulse response (FIR) filter coefficients indexed by signal amplitude level, wherein the FIR filter coefficients incorporate the amplitude-dependent and frequency-dependent variations in the gain and phase rotation; and
cascading a bulk stage that incorporates the bulk estimates of the gain, phase rotation and delay with a filter stage that filters an input signal using the FIR filter coefficients stored in the data structure, wherein the filter stage selects sets of FIR filter coefficients from the data structure for use based at least upon a current amplitude of the input signal. - View Dependent Claims (48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60)
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61. A method of modeling a frequency response of a wideband amplifier, comprising:
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(a) stimulating the amplifier with a narrowband signal over substantially an entire input amplitude range of the amplifier while recording observation data that represents a resulting output of the amplifier;
(b) repeating (a) for each of a plurality of center frequencies of the narrowband signal such that the amplifier is stimulated over substantially an entire operating bandwidth; and
(c) for each of a plurality of discrete amplitude levels, using the observation data recorded in (a) and (b) to compute gain and phase responses of the amplifier for at least some of the plurality of center frequencies. - View Dependent Claims (62, 63, 64, 65, 66)
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67. A model of a non-linear wideband amplifier, the model comprising:
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a bulk stage that applies at least bulk gain, phase and delay adjustments to an input signal; and
a filter stage that further adjusts the input signal to account for at least frequency-dependent and amplitude-dependent variations in the gain and phase introduced by the amplifier, the filter stage comprising a data structure that supplies finite impulse response (FIR) filter coeficients to an FIR filter based at least upon a current amplitude or power of the input signal. - View Dependent Claims (68, 69, 70, 71, 72, 73, 74)
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75. A method of generating an initial set of compensation parameters, including filter coefficients, for use within a digital compensation circuit that predistorts an input signal to a wideband amplifier, the method comprising:
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generating an initial model of the wideband amplifier, wherein the initial model comprises a filter structure for which sets of coefficients are supplied by a multi-demensional data structure, wherein each dimension of the data structure corresponds to a different respective input signal characteristic and each storage element of the data structure stores a set of filter coefficients;
reducing the initial model of the amplifier to a first order, single kernel model in which sets of filter coefficients are stored in a one-dimensional data structure; and
computing an initial set of the compensation parameters directly from the first order, single kernel model. - View Dependent Claims (76, 77)
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Specification