EP-4738702-A1 - PRE-DISTORTION SYSTEMS FOR A BAND LIMITED LOOPBACK

EP4738702A1EP 4738702 A1EP4738702 A1EP 4738702A1EP-4738702-A1

Abstract

A digital pre-distortion achieving near ideal spectral regrowth suppression with a bandlimited loopback. To eliminate mismatch between the bandwidth of the pre-distortion model terms and the bandwidth of the signal used to determine the model a band limiting operation may be applied to both the loopback signal and the input to the power amplifier used for estimating the pre-distortion coefficients. In addition, oversampling may be performed in the digital domain to avoid aliasing in the nonlinear terms of the pre-distortion model.

Inventors

SULIMARSKI, AVI
Yaish, Israel

Assignees

Avago Technologies International Sales Pte. Limited

Dates

Publication Date: 20260506
Application Date: 20251014

Claims (15)

A device comprising one or more circuits configured to perform operations comprising: performing a digital pre-distortion of a signal; generating a digital loopback signal by sampling a loopback signal of an amplifier at a band limiting sampling frequency; upsampling the digital loopback signal by interpolating between samples of the digital loopback signal; and estimating parameters of a digital pre-distortion model using the upsampled digital loopback signal.
The device of claim 1, wherein the band limiting sampling frequency is less than or equal to two times a bandwidth of the signal and a sampling frequency of the upsampled digital loopback signal is at least two times the band limiting sampling frequency.
The device of claim 1 or 2, wherein the upsampled digital loopback signal reduces an aliasing effect of nonlinear terms of the digital pre-distortion model.
The device of any preceding claim, wherein estimating the parameters of the digital pre-distortion model comprises reducing error between an output of the digital pre-distortion and an output of the digital pre-distortion model using the upsampled digital loopback signal as input.
The device of claim 4, the operations further comprising: generating a band limited pre-distortion output signal by applying a band limiting operator to the output of the digital pre-distortion; and generating an estimated band limited pre-distortion output signal by applying the band limiting operator to the output of the digital pre-distortion model using the upsampled digital loopback signal as input, wherein estimating the parameters of the digital pre-distortion model is performed by reducing error between the band limited pre-distortion output signal and the estimated band limited pre-distortion output signal, in particular, wherein the digital pre-distortion model comprises a Volterra series and the band limiting operator is applied to each of a plurality of monomial expansion terms of the Volterra series of the digital pre-distortion model.
A device comprising one or more circuits configured to perform operations comprising: performing a digital pre-distortion of a signal; generating a digital loopback signal by sampling a loopback signal of an amplifier at a band limiting sampling frequency; generating a band limited pre-distortion output signal by applying a band limiting operator to an output of the digital pre-distortion; and estimating parameters of a digital pre-distortion model by reducing error between the band limited pre-distortion output signal and an output of the digital pre-distortion model using the digital loopback signal as input, wherein the band limiting operator is applied to each of a plurality of monomial expansion terms of the digital pre-distortion model.
The device of claim 6, wherein estimating the parameters of the digital pre-distortion model is performed using a least squares estimation technique, and/or wherein the plurality of monomial expansion terms comprises terms from a discrete Volterra series.
The device of claim 6 or 7, the operations further comprising upsampling the digital loopback signal to reduce an aliasing effect of nonlinear terms of the digital pre-distortion model, in particular, wherein the band limiting sampling frequency is less than or equal to two times a bandwidth of the signal a sampling frequency of the upsampled digital loopback signal is at least two times the band limiting sampling frequency.
The device of any preceding claim, wherein a transmitter using the amplifier is not bandlimited between the amplifier and a coupler used to generate the loopback signal.
A device comprising one or more circuits configured to perform operations comprising: performing a digital pre-distortion of a signal; acquiring a digital loopback signal by sampling a loopback signal of an amplifier; generating a band limited pre-distortion output signal by applying a band limiting operator to an output of the digital pre-distortion of the signal; upsampling the digital loopback signal by interpolating between samples of the digital loopback signal; generating an estimated band limited pre-distortion output signal by applying the band limiting operator to the output of a digital pre-distortion model using the upsampled digital loopback signal as input; and estimating parameters of the digital pre-distortion model by reducing error between the band limited pre-distortion output signal and the estimated band limited pre-distortion output signal.
The device of claim 10, wherein estimating the parameters of the digital pre-distortion model is performed using a least squares estimation technique.
The device of claim 11, wherein the digital pre-distortion model comprises a plurality of monomial expansion terms, and wherein generating an estimated band limited pre-distortion output comprises applying the band limiting operator to each of the plurality of monomial expansion terms.
The device of any of claims 10 to 12, wherein applying the band limiting operator reduces frequencies outside a frequency band of the signal.
The device of any of claims 10 to 13, wherein a sampling frequency of the upsampled digital loopback signal is at least two times the sampling frequency of the digital loopback signal.
The device of any of claims 1 to 5 and 10 to 14, wherein interpolating between samples is performed using at least one of: linear interpolation; polynomial interpolation; spline interpolation; or trigonometric interpolation.

Description

BACKGROUND The present disclosure relates to pre-distortion used to compensate for nonlinearities in a power amplifier. In certain applications accurate pre-distortion are necessary to suppress spectral regrowth and obtain optimal error vector magnitude (EVM). The digital pre-distortion feedback is often restricted by non-ideal components that limit bandwidth such as the anti-aliasing filter and the analog-to-digital converter sampling rate. Limited bandwidth can affect the capability of the pre-distortion technique making high throughput and wide band applications difficult, especially inexpensively and at usable distances. BRIEF DESCRIPTION OF THE DRAWINGS Various objects, aspects, features, and advantages of the disclosure will become more apparent and better understood by referring to the detailed description taken in conjunction with the accompanying drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. FIG. 1A is a block diagram depicting a network environment including one or more access points in communication with one or more devices or stations, according to some embodiments.FIG. 1B is a block diagrams depicting computing devices useful in connection with the methods and systems described herein, according to some embodiments.FIG. 1C is another block diagrams depicting computing devices useful in connection with the methods and systems described herein, according to some embodiments.FIG. 2 is a block diagram of an amplifying device performing digital pre-distortion device, according to some embodiments.FIG. 3 is a block diagram of the memory digital pre-distortion circuit of FIG. 2, according to some embodiments.FIG. 4A is a block diagram of the model estimator circuit of FIG. 2, according to some embodiments.FIG. 4B is a block diagram of the memory digital pre-distortion model circuit of FIG. 4A, according to some embodiments.FIG. 5A is another block diagram of the model estimator circuit of FIG. 2, according to some embodiments.FIG. 5B is a block diagram of the memory digital pre-distortion model circuit of FIG. 5A subject to a band limiting operation, according to some embodiments.FIG. 6 is a flow diagram for performing digital pre-distortion using an upsampled digital loopback signal, according to some embodiments.FIG. 7 is a flow diagram for performing digital pre-distortion by applying a band limiting operation to both the output of the digital pre-distortion model circuit and the input the power amplifier, according to some embodiments.FIG. 8 is a flow diagram for performing digital pre-distortion by applying a band limiting operation to both the output of the digital pre-distortion model circuit and the input the power amplifier and upsampling a digital loopback signal, according to some embodimentsFIG. 9 is a plot of power as a function of frequency demonstrating improved adjacent channel power ratio (ACPR), according to some embodiments.FIG. 10 is a plot of error vector magnitude (EVM) as a function of output power, according to some embodiments. DETAILED DESCRIPTION Some embodiments relate to a digital pre-distortion that achieves near ideal spectral regrowth suppression with a bandlimited loopback signal when compared to a loopback signal that has very wide bandwidth (e.g., would require expensive components to sample the analog-to-digital at a very fast rate). The systems and methods of the present disclosure are able to overcome issues related to the bandlimited loopback signal. To eliminate mismatch between the bandwidth of the pre-distortion model output and the bandwidth of the signal used to determine the model, a band limiting operation may be applied to both the loopback signal and the input to the power amplifier used for estimating the pre-distortion model. In addition, oversampling may be performed in the digital domain to avoid aliasing in the nonlinear terms of the model. An embodiment relates to device including one or more circuits configured to perform operations. The operations include performing a digital pre-distortion of a signal. The operations include generating a digital loopback signal by sampling a loopback signal of an amplifier at a band limiting sampling frequency. The operations also include upsampling the digital loopback signal by interpolating between samples of the digital loopback signal. The operations also include estimating parameters of a digital pre-distortion model using the upsampled digital loopback signal. Digital pre-distortion of a signal refers to applying an inverse operation (e.g., a canceling operation) to a signal prior to signal amplification where the inverse operation is designed to compensate for the effects of nonlinearities in the amplification process in some embodiments. For example, digital pre-distortion may refer to polynomial pre-distortion, memory digital pre-di