Outphasing PA Compensator Split Into Short- and Long-Memory Stages
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Solution Overview
Problem
Outphasing power amplifiers struggle to achieve high linearity levels, especially at high signaling rates, due to severe memory effects that make existing predistortion techniques complex and inefficient, leading to power-added efficiency degradation.
Innovation Solution
The implementation of digital compensation circuits that partition the compensator into a long-memory linear time-invariant portion and a short-memory nonlinear portion, along with modifications to the shaping filter, such as zero-avoidance or level-avoidance functionality, to improve linearity and reduce hardware complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional Volterra-based predistortion techniques are used to improve linearity, then linearity levels improve, but device complexity and hardware requirements increase significantly
Solution Approach 1:
The compensator is divided into two distinct stages: a first stage implementing non-linear transformations with short memory effects, and a second stage implementing linear time-invariant transformations with long memory effects. This segmentation allows each stage to be optimized independently, reducing overall hardware complexity while maintaining linearity performance.
Solution Approach 2:
The patent replaces complex Volterra-based predistortion hardware with a simplified two-stage digital compensation architecture. The first stage uses non-linear transformations to handle immediate distortions, while the second stage uses LTI filtering to address memory effects, eliminating the need for complex Volterra series computation hardware.
2Productivity
If high signaling rates are used to improve throughput, then productivity increases, but memory effects become more severe degrading linearity
Solution Approach 1:
The compensator applies non-linear transformations in the first stage before the signal enters the LTI filtering stage. This preliminary non-linear compensation addresses distortion components before they are further processed, preventing memory effects from accumulating and degrading linearity at high signaling rates.
Solution Approach 2:
The patent implements a dynamic compensation architecture where the first stage handles time-varying non-linear effects with short memory, while the second stage handles more gradual LTI effects. This dynamic division allows the system to adapt to different signaling rates and memory effect characteristics.
3Manufacturing precision
If complex predistortion circuits are implemented to improve linearity, then linearity improves, but power consumption increases degrading power-added efficiency
Solution Approach 1:
By segmenting the compensator into two specialized stages, each handling specific types of distortions, the patent avoids the need for a single complex predistortion circuit. This segmentation allows for more efficient hardware implementation with lower power consumption while achieving the same linearity improvement.
Solution Approach 2:
The patent changes the approach from using complex Volterra series parameters to using simpler non-linear transformation parameters in the first stage followed by LTI filter parameters in the second stage. This parameter simplification reduces computational complexity and power consumption while maintaining linearity performance.
4Manufacturing precision
If long-memory compensation is used to address memory effects, then linearity improves, but device complexity and processing requirements increase
Solution Approach 1:
The patent separates long-memory LTI compensation into a dedicated second stage that follows a simpler first stage. This segmentation allows the complex long-memory processing to be isolated and optimized independently, reducing overall processing complexity compared to attempting to handle all effects in a single stage.
Solution Approach 2:
The first stage acts as an intermediary that pre-processes the signal by removing immediate non-linear distortions before the signal enters the second stage for long-memory LTI compensation. This intermediary processing simplifies the requirements for the long-memory stage, reducing overall processing complexity.
Data Source
AI summary
Digital compensators for use in outphasing-based power amplification systems (e.g., Linear Amplification using Nonlinear Components (LINC) amplifiers and Asymmetric Multilevel Outphasing (AMO) amplifiers) include a short memory nonlinear portion and a long memory linear time invariant (LTI) portion. In various embodiments, compensators are provided that are of relatively low complexity and that are capable of operation at throughputs exceeding a Gigasample per second.