Digital predistortion system and method for correcting memory effects within an RF power amplifier
First Claim
1. A digital predistorter adapted to receive a digital input signal and output a predistorted digital signal, the digital predistorter comprising:
- an input coupled to receive the digital input signal;
a first signal path coupled to the input and comprising a delay circuit and a combiner circuit coupled to the output of the delay circuit;
a second signal path, coupled to the input in parallel with said first signal path, comprising a first digital predistorter circuit providing a first predistortion operation on the input signal; and
a third signal path, coupled to the input in parallel with said first and second signal path, comprising a second digital predistorter circuit providing a second different predistortion operation on the input signal;
wherein the combiner circuit receives and combines the outputs of the first and second digital predistorter circuits with the output of the delay circuit of the first signal path to provide a predistorted digital output signal.
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Accused Products
Abstract
A system and method of correcting memory effects present within power amplifiers using digital predistortion and an improved power amplifier system employing digital predistortion are disclosed. Nonlinearities within a power amplifier having an input derived from a digital signal are compensated by injecting a digital correction signal prior to the power amplifier. A system and method for modeling the distortion created by power amplifier memory effects and generating the desired digital predistortion correction signal are disclosed.
62 Citations
50 Claims
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1. A digital predistorter adapted to receive a digital input signal and output a predistorted digital signal, the digital predistorter comprising:
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an input coupled to receive the digital input signal;
a first signal path coupled to the input and comprising a delay circuit and a combiner circuit coupled to the output of the delay circuit;
a second signal path, coupled to the input in parallel with said first signal path, comprising a first digital predistorter circuit providing a first predistortion operation on the input signal; and
a third signal path, coupled to the input in parallel with said first and second signal path, comprising a second digital predistorter circuit providing a second different predistortion operation on the input signal;
wherein the combiner circuit receives and combines the outputs of the first and second digital predistorter circuits with the output of the delay circuit of the first signal path to provide a predistorted digital output signal. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A digital predistortion circuit adapted to receive a digital input signal and output a digital predistortion correction signal compensating for memory effects due to plural samples of the input signal, the digital predistortion circuit comprising:
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an input for receiving the digital input signal;
a first signal path comprising a delay circuit coupled to the input and a combiner circuit coupled to the output of the delay circuit;
a filter bank, coupled to the input and configured in parallel with the first signal path, the filter bank comprising at least two filters having different frequency responses and outputting at least first and second band limited signals derived from plural samples of the digital input signal; and
a plurality of nonlinear operation circuits coupled to the filter bank and receiving the band limited signals, the nonlinear operation circuits creating higher order signals from the band limited signals;
wherein the outputs of the nonlinear operation circuits are provided to the combiner circuit in the first signal path and combined with the delayed input signal output from the delay circuit in the first signal path to provide a digital predistortion output signal. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A digital predistortion circuit adapted to receive a digital input signal and output a digital predistortion signal compensating for memory effects due to plural samples of the input signal, the digital predistortion circuit comprising:
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an input for receiving the digital input signal;
a first signal path comprising a delay circuit coupled to the input and a combiner circuit coupled to the output of the delay circuit;
a nonlinear operation circuit coupled to the input and configured in parallel with the first signal path and receiving the digital input signal, the nonlinear operation circuit creating a higher order signal from the digital input signal; and
a filter bank, coupled to the nonlinear operation circuit and receiving the higher order signal, the filter bank comprising plural filters having different frequency responses and outputting plural band limited higher order signals derived from plural samples of the higher order signal;
wherein the outputs of the filters are provided to the combiner circuit in the first signal path and combined with the delayed input signal output from the delay circuit in the first signal path to provide a digital predistortion output signal. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. A digital predistortion circuit adapted to receive a digital input signal and output a digital predistortion signal compensating for memory effects due to plural samples of the input signal, the digital predistortion circuit comprising:
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an input for receiving the digital input signal;
a filter bank comprising at least two filters having different frequency responses and outputting at least first and second band limited signals derived from plural samples of the digital input signal;
a plurality of nonlinear operation circuits coupled to the filter bank and receiving the band limited signals, the nonlinear operation circuits creating third order or higher order signals from the band limited signals; and
one or more combiner circuits receiving and combining the outputs of the nonlinear operation circuits to provide a digital predistortion output signal. - View Dependent Claims (22, 23, 24, 25, 26)
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27. A digital predistortion circuit adapted to receive a digital input signal and output a digital predistortion signal compensating for memory effects due to plural samples of the input signal, the digital predistortion circuit comprising:
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an input for receiving the digital input signal;
a nonlinear operation circuit coupled to the input and receiving the digital input signal, the nonlinear operation circuit creating third or higher order signals from the digital input signal;
a filter bank, coupled to the nonlinear operation circuit and receiving the third or higher order signals, the filter bank comprising plural filters having different frequency responses and outputting plural band limited third order or higher order signals derived from plural samples of the third or higher order signal; and
one or more combiner circuits receiving and combining the outputs of the filters to provide a predistortion output signal. - View Dependent Claims (28, 29, 30, 31, 32)
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33. An adaptive digital predistortion system adapted to receive a digital input signal and output a predistorted digital signal to a nonlinear component and to receive a digital sample of the output of the nonlinear component, the digital predistortion system comprising:
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an input coupled to receive the digital input signal;
a digital predistorter module coupled to the input and comprising a predistortion circuit operating on the digital input signal to create band limited signals from the input signal and employing separate predistortion coefficients for weighting the band limited signals;
an error generator circuit for receiving the digital input signal and the digital sample of the output of the nonlinear component and providing a digital error signal; and
an adaptive coefficient generator coupled to receive the digital input signal and the digital error signal and comprising a spectral weighting circuit to derive separately weighted frequency components from the input signal and error signal and a coefficient estimator circuit for calculating updated predistortion coefficients weighted differently for different frequency components and providing the updated predistortion coefficients to the digital predistorter module. - View Dependent Claims (34, 35, 37, 38)
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39. A linearized amplifier system adapted to receive a digital input signal and output an amplified RF signal, comprising:
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an input coupled to receive the digital input signal;
a digital predistorter module comprising a first signal path coupled to the input and comprising a delay circuit and a combiner circuit coupled to the output of the delay circuit, a second signal path coupled to the input in parallel with said first signal path and comprising a first digital predistorter circuit providing a memoryless predistortion operation on the input signal operating on single samples of the input signal, and a third signal path coupled to the input in parallel with said first and second signal paths and comprising a second digital predistorter circuit providing a memory based predistortion operation on the input signal employing plural samples of the input signal, wherein the combiner circuit receives and combines the outputs of the first and second digital predistorter circuits with the output of the delay circuit of the first signal path to provide a predistorted digital signal;
a digital to analog converter coupled to receive the predistorted digital signal from the digital predistorter module and provide a predistorted analog signal;
an up converter receiving the predistorted analog signal from the digital to analog converter and converting it to an RF analog signal; and
a power amplifier receiving the RF analog signal and providing an amplified RF output signal.
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40. An adaptively linearized amplifier system, comprising:
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an input coupled to receive a digital input signal;
a digital predistorter module coupled to the input and receiving the digital input signal and outputting a predistorted digital signal, the digital predistorter module comprising a predistortion circuit operating on the digital input signal to create band limited signals from the input signal and employing separate predistortion coefficients for weighting the band limited signals;
a digital to analog converter coupled to receive the predistorted digital signal output of the digital predistorter module and provide an analog signal;
an up converter for receiving the analog signal from the digital to analog converter and converting it to an RF analog signal;
a power amplifier receiving the RF analog signal and providing an amplified RF output signal;
an output sampling coupler coupled to sample the analog RF output signal from the power amplifier;
a feedback circuit path, coupled to the output sampling coupler, comprising a down converter and an analog to digital converter converting the sampled RF output signal to a digital sampled signal representative of the RF output signal;
an error generator circuit coupled to the input and the feedback circuit path for receiving the digital input signal and the digital sampled signal and providing a digital error signal; and
an adaptive coefficient generator, coupled to receive the digital input signal and the digital error signal and providing updated predistortion coefficients to the digital predistorter module, comprising a spectral weighting circuit to derive separately weighted frequency components from the digital input signal and digital error signal and a coefficient estimator circuit for calculating updated predistortion coefficients weighted differently for different frequency components.
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41. A method for digitally predistorting a digital input signal, comprising:
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receiving a digital input signal and splitting the digital input signal along three parallel signal paths;
delaying the signal provided along the first signal path;
digitally predistorting the signal provided along the second signal path employing a single sample of the input signal to provide a memoryless predistortion correction;
digitally predistorting the signal along the third signal path employing plural samples of the input signal to provide a memory based digital predistortion correction; and
combining the memoryless and memory based digital predistortion corrections provided from the second and third signal paths with the delayed signal in the first signal path to provide a predistorted digital output signal.
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42. A method for digitally predistorting a digital input signal, comprising:
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receiving a digital input signal;
deriving a plurality of band limited higher order signals from the digital input signal;
weighting the plurality of band limited higher order signals with predistortion coefficients varying between the band limited higher order signals to provide a predistortion correction signal; and
combining the predistortion correction signal with the digital input signal to provide a predistorted digital output signal. - View Dependent Claims (43, 44, 45, 46, 47)
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48. A method for digitally predistorting a digital input signal, comprising:
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receiving a digital input signal;
deriving a plurality of higher order signals representative of nonlinear basis functions based on a joint time frequency representation of plural samples of the digital input signal;
weighting the plurality of higher order signals with predistortion coefficients to provide a predistortion correction signal; and
combining the predistortion correction signal with the digital input signal to provide a predistorted digital signal. - View Dependent Claims (49)
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50. A method for adaptive digital predistortion linearization of an amplifier system, comprising:
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receiving a digital input signal;
deriving a plurality of band limited higher order signals from the digital input signal;
weighting the plurality of band limited higher order signals with spectrally weighted predistortion coefficients to provide a predistortion correction signal;
combining the predistortion correction signal with the digital input signal to provide a predistorted digital signal;
converting the predistorted digital signal from digital to analog form to provide a predistorted analog signal;
up converting the predistorted analog signal to an RF signal;
amplifying the RF signal to provide an amplified RF output signal;
sampling the RF output signal;
down converting the sampled RF output signal to a lower frequency sampled analog output signal;
converting the lower frequency sampled analog output signal to digital form to provide a sampled digital output signal;
deriving an error signal from the input digital signal and the sampled digital output signal;
deriving spectrally weighted subsignals from the error signal and the digital input signal; and
adaptively generating said spectrally weighted predistortion coefficients from the spectrally weighted subsignals.
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Specification