Adaptive Predistorter Circuit for Low-Rate PA Nonlinearity Identification
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current communication systems face challenges in minimizing spectral regrowth and intermodulation distortion due to the nonlinear behavior of power amplifiers, particularly when operating in the nonlinear region, which is costly to mitigate using oversized transistors or requires high sampling rates for predistortion.
Innovation Solution
A circuit with an adaptive predistorter that identifies the nonlinearity of power amplifiers at a lower sampling rate, using Volterra kernel identification and upsampling to translate predistortion control parameters, allowing for efficient predistortion even when the power amplifier is driven in the nonlinear region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high sampling rates are used for predistortion identification, then spectral regrowth and intermodulation distortion are minimized, but cost and complexity increase
Solution Approach 1:
The patent segments the predistortion process into two distinct stages: identification stage operating at reduced sampling rate (Nyquist rate of input signal) and execution stage operating at high sampling rate. This segmentation allows the system to achieve accurate predistortion parameters without continuously operating at high sampling rates, thereby reducing overall complexity while maintaining effectiveness in minimizing spectral regrowth and intermodulation distortion.
Solution Approach 2:
The patent applies preliminary action by performing the computationally intensive identification and parameter calculation at a reduced sampling rate before the actual predistortion execution. The identification unit determines predistortion parameters offline or in advance, which are then used during normal operation. This preliminary computation reduces the real-time processing burden and allows the system to achieve high-performance predistortion without requiring continuous high sampling rate operation.
2Object-affected harmful factors
If oversized power transistors are used to operate in linear range, then spectral regrowth is minimized, but cost and efficiency deteriorate
Solution Approach 1:
The patent applies preliminary anti-action by introducing a predistorter that pre-compensates for the nonlinear effects of the power amplifier before the signal enters the amplifier. The predistorter applies an inverse nonlinearity that counteracts the amplifier's nonlinearity, thereby preventing spectral regrowth from occurring in the first place. This allows the power amplifier to operate efficiently in its nonlinear region without requiring oversized transistors, thus maintaining both low cost and high efficiency while minimizing harmful spectral regrowth.
3Loss of energy
If power amplifier is driven in nonlinear region, then efficiency is improved, but spectral regrowth and intermodulation distortion increase
Solution Approach 1:
The patent implements feedback by using an identification unit that measures the actual output of the power amplifier and uses this information to determine accurate predistortion parameters. The system continuously monitors the amplifier's nonlinear behavior and adjusts the predistorter parameters accordingly. This feedback mechanism enables the system to maintain high efficiency operation in the nonlinear region while dynamically compensating for spectral regrowth and intermodulation distortion, achieving both high efficiency and low distortion simultaneously.
Data Source
AI summary
In one embodiment, a circuit comprises an adaptive predistorter and a nonlinear element coupled to an output of the predistorter. The predistorter is operative to predistort an input signal according to predistortion control parameters at a given sampling rate. The circuit further comprises an identification unit and a translation unit. The identification unit identifies nonlinearity parameters representing the nonlinearity of the nonlinear element by sampling the output of the nonlinear element at an identification sampling rate lower than twice a bandwidth at the output of the nonlinear element. The translation unit translates the identified nonlinearity parameters into the predistortion control parameters. Other systems and methods are disclosed.