RF Pre-Distorter Feedback Adaptation for Faster PA Linearization
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Solution Overview
Problem
Conventional power amplifier linearization techniques face challenges in efficiently reducing non-linearity while maintaining amplifier efficiency, especially with modern wide bandwidth modulation schemes, and existing RF domain pre-distortion methods suffer from slow convergence and potential mismatches due to circuit non-idealities.
Innovation Solution
A pre-distorter generates an error signal to adapt pre-distortion weights iteratively, using a digital domain calculation and spectral performance module to minimize non-linearity, with a linear transformation of coefficients to enhance convergence speed and independence of error dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional baseband pre-distortion is used to reduce non-linearity, then distortion is reduced, but power consumption increases and system complexity increases due to unnecessary digitization
Solution Approach 1:
The patent replaces the conventional baseband digital domain pre-distortion system with an RF domain pre-distortion system. Instead of digitizing the RF signal and processing it in the digital domain, the invention performs pre-distortion directly in the RF domain using analog circuitry, thereby eliminating unnecessary digitization and reducing power consumption while maintaining distortion reduction capabilities
Solution Approach 2:
The patent introduces an RF domain pre-distorter as an intermediary component between the modulator and power amplifier. This pre-distorter processes the RF signal directly without requiring baseband conversion, serving as a mediator that reduces distortion while avoiding the power consumption penalties of full digital processing chains
2Use of energy by moving object
If RF domain pre-distortion is used to reduce power consumption, then power consumption is reduced, but convergence speed decreases and mismatches occur due to circuit non-idealities
Solution Approach 1:
The patent implements a feedback mechanism in the RF domain pre-distortion system where the output of the power amplifier is fed back to the pre-distorter. This feedback loop enables the pre-distorter to continuously adjust its pre-distortion coefficients based on the actual output, thereby achieving fast convergence despite operating in the RF domain with analog circuitry
Solution Approach 2:
The RF domain pre-distorter performs self-adjustment by using its own output and feedback from the power amplifier to automatically tune its pre-distortion parameters. This self-service capability allows the system to converge quickly without requiring external control or complex digital processing
3Object-generated harmful factors
If amplifier operates in linear region below maximum power capacity to reduce distortion, then distortion is reduced, but amplifier efficiency decreases and system becomes less efficient
Solution Approach 1:
The patent applies preliminary pre-distortion to the RF signal before it enters the power amplifier. By pre-distorting the signal in advance to compensate for the amplifier's non-linear characteristics, the amplifier can operate at higher power levels closer to saturation while still producing linear output, thereby maintaining both low distortion and high efficiency
Solution Approach 2:
The patent changes the parameters of the input signal by applying pre-distortion transformation. The pre-distorter modifies the amplitude and phase parameters of the RF signal in advance, creating a pre-distorted signal that, when amplified by the non-linear power amplifier, results in a linear output signal with preserved efficiency
4Object-generated harmful factors
If pre-distortion coefficients are iteratively adapted to minimize error, then non-linearity is reduced, but convergence is slow and false minimums may occur
Solution Approach 1:
The patent segments the pre-distortion coefficient adaptation process into independent error dimensions. By decomposing the error space into separate dimensions that can be minimized independently, the system avoids the slow convergence and false minimum problems associated with coupled error dimensions, achieving faster convergence while effectively reducing non-linearity
Data Source
AI summary
A pre-distorter is provided for distorting an RF input signal to provide a pre-distorted radio frequency (RF) input signal to an amplifier that provides an amplified RF output signal, wherein the RF input signal has an envelope. The pre-distorter includes: a radio-frequency signal processing circuit that distorts the RF input signal according to a polynomial of powers of the envelope, each power of the envelope being weighted by a corresponding pre-distortion weight; and a performance monitor operable to compare a version of the amplified RF output signal to a delayed version of the RF input signal to provide an error signal, wherein the performance monitor is configured to iteratively adapt the coefficients based upon a gradient of a cost function, the cost function being a function of the error signal.