Power Amplifier Predistortion Using Current and Previous Signal Memory
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Solution Overview
Problem
Existing distortion compensation techniques face challenges in achieving high linearity and power conversion efficiency in power amplifiers due to the memory effect, which complicates the convergence of distortion compensation coefficients and increases circuit complexity, leading to insufficient distortion suppression performance.
Innovation Solution
A distortion compensation apparatus that generates multiple distortion compensation coefficients based on both current and previous input signals using a Volterra series and look-up tables, with address generation units creating addresses for stored coefficients to perform pre-distortion processing, effectively addressing the memory effect and thermal memory impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the delay amount of the power series is increased to improve distortion suppression effect, then the distortion suppression performance is improved, but the number of delay circuits increases resulting in increased circuit scale
Solution Approach 1:
The patent divides the distortion compensation function into multiple independent lookup tables, each storing coefficients for specific delay amounts. This segmentation allows the system to achieve high distortion suppression performance without requiring a single large delay circuit, thereby reducing overall circuit scale while maintaining reliability.
Solution Approach 2:
Different lookup tables store distortion compensation coefficients for different delay amounts, allowing each table to be optimized for specific local conditions. This enables precise distortion compensation for each delay scenario without requiring all possible delay circuits to be simultaneously present, thus improving performance while controlling circuit complexity.
2Reliability
If the number of distortion compensation coefficients is increased to improve distortion suppression effect, then the distortion suppression performance is improved, but the convergence difficulty of coefficients increases
Solution Approach 1:
The patent segments the large set of distortion compensation coefficients into multiple smaller sets, with each lookup table containing coefficients for a specific delay amount. This segmentation reduces the number of coefficients that need to converge simultaneously, making the adaptation process more manageable while still achieving high distortion suppression performance through the combined effect of all tables.
Solution Approach 2:
The patent uses multiple lookup tables that may store more coefficients than strictly necessary for basic distortion compensation. This excessive storage of coefficients in organized groups allows the system to achieve better distortion suppression while keeping each individual table's coefficient set manageable for convergence, balancing performance improvement with convergence feasibility.
3Device complexity
If a single lookup table is used to store distortion compensation coefficients, then the circuit scale is reduced, but the distortion suppression performance is insufficient
Solution Approach 1:
The patent divides the single large lookup table into multiple smaller lookup tables, each handling specific delay amounts. This segmentation improves distortion suppression performance by allowing specialized coefficient storage for each delay scenario while keeping individual table sizes manageable, thus achieving high performance without excessive circuit scale.
Solution Approach 2:
The patent transitions from a single-dimensional lookup table structure to a multi-dimensional structure with multiple tables indexed by both input signal level and delay amount. This dimensional expansion enables the system to achieve superior distortion suppression performance while maintaining reasonable circuit scale through efficient organization of coefficients across multiple tables.
Data Source
AI summary
A distortion compensation apparatus includes an amplifying unit, a plurality of distortion compensation coefficient storage units, a first address generating unit, a second address generating unit, and a distortion compensating unit. The amplifying unit amplifies an input signal. A plurality of distortion compensation coefficient storage units store the distortion compensation coefficients for compensating for the distortion of the amplifying unit by being associated with two different addresses. The first address generating unit generates a first address based on the current input signal. The second address generating unit generates a second address different from the first address based on the previous input signal. The distortion compensating unit obtains the distortion compensation coefficient corresponding to a combination of the first and second addresses from each of the distortion compensation coefficient storage units and performs a pre-distortion processing for the current input signal to the amplifying unit using the obtained distortion compensation coefficient.