Memory-Polynomial LUT Predistortion for Efficient Power Amplifiers
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Solution Overview
Problem
Power amplifiers in wireless transmitters face inefficiencies when operating in a backed-off state to avoid signal distortion, leading to non-optimal transmission due to high peak-to-average power ratio (PAPR) in modern wireless modulation formats.
Innovation Solution
Implementing a direct-to-LUT digital pre-distortion method using memory polynomial look-up-table (LUT) circuitry and post-distortion updates to correct for distortion in power amplifiers, eliminating the need for a digital signal processor (DSP) by applying distortion to signals before amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power amplifier operates in a backed off state to avoid compression, then signal distortion is reduced, but power efficiency deteriorates
Solution Approach 1:
The pre-distortion circuitry applies inverse distortion to the input signal before it reaches the power amplifier. By pre-distorting the signal in advance with characteristics that are opposite to the PA's non-linearities, the system compensates for upcoming distortion, allowing the PA to operate at higher power levels without actually producing distorted output.
Solution Approach 2:
The system uses feedback from the power amplifier output to continuously update and refine the pre-distortion characteristics. The post-distortion circuitry monitors the actual output and adjusts the pre-distortion parameters accordingly, creating a closed-loop system that maintains optimal performance while enabling operation closer to the compression region.
2Use of energy by moving object
If the power amplifier operates closer to the compression region, then power efficiency is improved, but signal distortion increases
Solution Approach 1:
The pre-distortion circuitry applies a corrective transformation to the input signal that is specifically designed to counteract the non-linear distortion that will occur in the power amplifier. By applying this preliminary anti-distortion, the system enables the PA to operate in the compression region while the pre-applied correction ensures the output remains linear and undistorted.
Solution Approach 2:
The system dynamically adjusts the pre-distortion parameters based on operating conditions. By changing the characteristics of the pre-distortion function according to the actual power amplifier behavior at different operating points, the system maintains optimal compensation across varying power efficiency requirements.
3Reliability
If complex pre-distortion algorithms are used to linearize the signal, then signal quality is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex computational algorithms with a hardware-based lookup table (LUT) system. Instead of performing complex real-time calculations to determine pre-distortion parameters, the system uses pre-computed values stored in LUTs that can be quickly accessed and applied, substituting mechanical/computational complexity with simpler memory-based retrieval.
Solution Approach 2:
The system uses lookup tables that contain pre-computed pre-distortion characteristics copied from offline calculations or measurements. Rather than computing complex distortion compensation in real-time, the system copies and applies pre-determined correction values from the LUTs, significantly reducing real-time computational requirements while maintaining accuracy.
Data Source
AI summary
A distortion apparatus for a power amplifier comprises: pre-distortion circuitry that comprises a memory polynomial look-up-table (LUT) circuit; and post-distortion circuitry that updates the pre-distortion circuitry based on an output of the power amplifier. The pre-distortion circuitry comprises a plurality of LUTs. Each LUT corresponds to a different memory depth of a memory polynomial of a Volterra series. Each LUT indexed by an instantaneous power of an input sample delayed by an amount corresponds to a respective memory depth of each LUT. An output of the memory polynomial LUT circuit corresponds to a summation of an output of each LUT multiplied by the input sample delayed by the amount corresponding to the respective memory depth of each LUT, and an output of the pre-distortion circuitry is provided to the power amplifier.