Adaptive Subband Predistortion for RF Amplifier Linearity
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Solution Overview
Problem
High-efficiency RF power amplifiers, such as envelope elimination and restoration (EER) amplifiers, suffer from poor linearity due to nonlinearities and memory effects, leading to significant signal distortion, especially when amplifying wideband signals, which complicates the construction of practical predistortion signal processors.
Innovation Solution
An adaptive sub-band predistortion method that isolates sub-band signals, modifies their amplitude and phase using complex signal weighting parameters, and sums them to create a predistorted input signal, effectively addressing nonlinearities and memory effects in RF power amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If high-efficiency RF power amplifiers (such as EER amplifiers) are used, then power consumption is reduced and efficiency is improved, but linearity deteriorates and signal distortion increases
Solution Approach 1:
The patent divides the wideband input signal into multiple frequency sub-bands using a filter bank. Each sub-band signal is processed independently through separate predistortion paths, allowing targeted correction of nonlinearities and memory effects in different frequency regions. The corrected sub-band signals are then recombined to form the final predistorted output signal.
Solution Approach 2:
The patent employs adaptive predistortion filters with time-varying coefficients that dynamically adjust to compensate for memory effects in the power amplifier. The predistortion parameters are continuously updated based on feedback from the amplifier output, enabling the system to adapt to changing operating conditions and maintain optimal linearity across varying signal levels and frequencies.
2Speed
If wideband signals are amplified, then communication bandwidth is increased, but memory effects and nonlinearities become more significant, worsening linearity
Solution Approach 1:
The patent segments the wideband signal into multiple narrowband sub-bands, each processed through dedicated predistortion filters. This segmentation allows the system to handle memory effects more effectively in each sub-band while maintaining overall wideband performance, as the memory effects are localized and can be corrected independently in each frequency band.
Solution Approach 2:
The patent transforms the predistortion problem from a single-wideband approach to a multi-dimensional approach by processing signals in the frequency domain through sub-band decomposition. This dimensional transformation allows independent optimization of predistortion parameters for different frequency regions, effectively managing memory effects across the entire bandwidth.
3Manufacturing precision
If traditional predistortion techniques are used, then some nonlinearities are corrected, but memory effects cause poor linearization performance
Solution Approach 1:
The patent implements dynamic predistortion with adaptive filters that continuously adjust their coefficients to track and compensate for memory effects. The adaptive nature of the system allows it to respond to changing amplifier characteristics over time, improving the reliability and robustness of linearization performance compared to static predistortion approaches.
Solution Approach 2:
The patent employs a feedback mechanism where the output of the power amplifier is sampled, processed through a delay element, and fed back to update the predistortion filter coefficients. This closed-loop feedback ensures that the predistortion parameters are continuously optimized based on actual amplifier performance, significantly improving linearization reliability in the presence of memory effects.
Data Source
AI summary
Predistorting an input signal prior to amplification in an RF power amplifier (206) includes isolating a plurality sub-band signals, each representing a portion of the input signal s(t). The method includes independently modifying an amplitude and a phase of each of the plurality of sub-band signals. The modification of the amplitude and/or phase is performed using a set of signal weighting parameters (weights) w and W, controlling linear and nonlinear modifications respectively, which are determined in an adaptive process by an adaptive controller (224). After modification, each of the sub-bands are summed together to obtain a predistorted input signal for an RF power amplifier (206).