Digital Predistortion Filters for Power Amplifier Memory Effects
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Solution Overview
Problem
Conventional power amplifiers for communications systems face challenges with non-linear distortion, memory effects, high cost, and power consumption, especially when handling multiple carrier signals, as they require significant power back-off to maintain acceptable intermodulation distortion levels, limiting efficiency and cost-effectiveness.
Innovation Solution
A digital predistortion (DPD) linearizer system that includes a characterizer to generate coefficients for a predistortion engine, which corrects for non-linearity and memory effects by using a matrix equation to compute weights for filtering the signal input, thereby linearizing the output of power amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power amplifiers are driven close to saturation point for maximum efficiency, then power efficiency is improved, but intermodulation distortion levels increase
Solution Approach 1:
The predistortion linearizer applies preliminary anti-action by introducing inverse non-linearity before the power amplifier. The characterizer analyzes the PA's non-linear characteristics and generates predistortion coefficients that pre-compensate for expected distortion, allowing the PA to operate at high efficiency while the predistorted signal cancels out intermodulation distortion products.
Solution Approach 2:
The system employs feedback mechanisms where the characterizer continuously monitors the power amplifier's output and adjusts the predistortion coefficients accordingly. This closed-loop approach enables the system to adapt to changing PA characteristics and maintain low distortion levels while operating at optimal efficiency points.
2Object-generated harmful factors
If conventional Lookup Table methods are used to correct non-linearity, then non-linear distortion is reduced, but memory effects are not effectively handled
Solution Approach 1:
The invention transitions from static Lookup Table parameters to dynamic parameters that adapt to signal characteristics. The characterizer analyzes instantaneous signal properties and adjusts predistortion coefficients in real-time, enabling effective compensation of memory effects that depend on signal bandwidth and power level variations.
Solution Approach 2:
The system implements dynamic adaptation where the predistortion parameters change continuously based on incoming signal characteristics. Unlike static LUT methods, this dynamic approach allows the linearizer to track and compensate for memory effects that vary with signal conditions, improving overall reliability.
3Reliability
If multiple separate power amplifiers are used for multiple carrier signals, then each carrier can be amplified independently, but cost and power consumption increase
Solution Approach 1:
The invention merges multiple carrier signal processing into a single power amplifier by applying predistortion linearization to the combined signal. The characterizer analyzes the composite multi-carrier signal and generates unified predistortion coefficients, allowing one PA to handle multiple carriers efficiently while maintaining signal independence through digital signal processing.
Solution Approach 2:
The predistortion linearizer provides universal functionality by enabling a single power amplifier to perform the work of multiple amplifiers. The system adapts to handle different carrier combinations and signal conditions, making the single PA multi-functional and eliminating the need for separate amplifier hardware for each carrier.
Data Source
AI summary
A linearizer and method. In a most general embodiment, the inventive linearizer includes a characterizer coupled to an input to and an output from said circuit for generating a set of coefficients and a predistortion engine responsive to said coefficients for predistorting a signal input to said circuit such that said circuit generates a linearized output in response thereto. In a specific application, the circuit is a power amplifier into which a series of pulses are sent during an linearizer initialization mode of operation. In a specific implementation, the characterizer analyzes finite impulse responses of the amplifier in response to the initialization pulses and calculates the coefficients for the feedback compensation filter in response thereto. In the preferred embodiment, the impulse responses are averaged with respect to a threshold to provide combined responses. In the illustrative embodiment, the combined responses are Fast Fourier Transformed, reciprocated and then inverse transformed. The data during normal operation is fed back to the data capture, corrected for distortion in the feedback path from the output of the amplifier, converted to basedband, synchronized and used to provide the coefficients for the predistortion linearization engine. As a result, in the best mode, each of the coefficients used in the predistortion linearization engine can be computed by solving the matrix equation HW=S for W, where W is a vector of the weights, S is a vector of predistortion linearization engine outputs, and H is a matrix of PA return path inputs as taught herein.