Digital Predistortion Filtering for Power Amplifier Memory Effects
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing digital predistortion methods for power amplifiers assume memoryless behavior, failing to account for significant memory effects such as thermal and environmental influences, leading to incomplete linearization of power amplifier responses.
Innovation Solution
The implementation of a system that combines short duration and long duration digital predistortion circuits with QR decomposition to synthesize compensating error signals, addressing both memoryless and memory-based distortion effects by partitioning processing steps into real-time executable components using commercially available programmable signal processors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If memoryless digital predistortion methods are used, then the system complexity is reduced, but the linearization effectiveness deteriorates due to unaccounted memory effects
Solution Approach 1:
The patent segments the predistortion processing into multiple independent blocks: a memoryless predistortion block for immediate correction and a separate digital filter block for memory effect correction. This segmentation allows each block to specialize in specific types of distortion correction, improving overall linearization effectiveness while keeping individual blocks computationally manageable.
Solution Approach 2:
The patent introduces an intermediary digital filter block that processes the output of the memoryless predistortion block. This intermediary component specifically addresses memory effects by filtering the predistorted signal through coefficients derived from system identification, thereby improving linearization precision without requiring complete redesign of the entire predistortion system.
2Manufacturing precision
If inverse modeling is used to compensate for memory effects, then the linearization effectiveness improves, but the computational cost and system complexity increase
Solution Approach 1:
The patent creates a simplified copy or model of the memory effects through a digital filter with coefficients derived from system identification. Instead of implementing the full inverse model of the non-linear system, the patent uses a filtered version that captures the essential memory effects, reducing computational complexity while maintaining adequate linearization precision.
Solution Approach 2:
The patent changes the parameters of the predistortion system by using filter coefficients that are adaptively derived from system identification rather than requiring complete inverse modeling. This parameter change allows the system to compensate for memory effects using simplified models with fewer computational requirements.
3Use of energy by moving object
If power amplifier operates at higher power levels, then the efficiency improves, but the distortion increases due to non-linear behavior
Solution Approach 1:
The patent applies preliminary predistortion action to the input signal before it reaches the power amplifier. By pre-compensating for both memoryless and memory effects through the cascaded predistortion blocks, the system enables the power amplifier to operate at higher power levels with improved efficiency while maintaining low distortion output.
Solution Approach 2:
The patent employs feedback mechanisms where system identification processes analyze the actual output of the power amplifier and adjust the predistortion filter coefficients accordingly. This feedback loop continuously optimizes the predistortion parameters to maintain linearization effectiveness as the power amplifier operates at higher efficiency levels.
Data Source
AI summary
System and methods for a digital linearization of a non linear element. Digital predistortion methods and circuitry for linearizing a non-linear element that address long or “memory” effects and shorter duration effects, these two predistortion functions are operated together in an adaptive fashion with the non-linear element to provide a highly linear system. A short duration predistortion block comprises an Nth order polynomial filter coupled to a programmable linear equalizer. The Nth order filter includes programmable non-linearities and variable delay taps. The Nth order filter may be configured to implement a non-sequential or a sequential ordered polynomial. The equalizer may, in a preferred embodiment, include circuitry for equalizing imbalances between real and complex signal values. The Nth order filter may implement a compound Volterra filter. The combined system of the predistortion circuitry and a non-linear element has a linear input-output signal response. Methods for initializing, parameterizing and adapting the system are disclosed.