Digital Predistortion Partitioning for Power Amplifier Memory Effects
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Solution Overview
Problem
Existing power amplifiers in communication systems, particularly in cellular networks, exhibit non-linear output characteristics due to transistor saturation, leading to distortion in RF signals, which is challenging to address with current digital predistortion methods that assume memoryless behavior and fail to account for long-term memory effects.
Innovation Solution
A system and method that incorporates a memoryless or short duration digital predistortion circuit, an adaptive long duration digital predistortion circuit, and a QR decomposition function to synthesize compensating error signals, effectively addressing both short and long-term memory effects in power amplifiers by partitioning processing steps into real-time executable components using commercially available signal processors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If digital predistortion methods assume memoryless behavior, then device complexity is reduced, but manufacturing precision deteriorates due to failure to account for long-term memory effects
Solution Approach 1:
The predistortion function is divided into two separate circuits: a memoryless predistortion circuit for immediate distortion compensation and a memory effect predistortion circuit for long-term memory effects. This segmentation allows each circuit to be optimized independently, maintaining manageable complexity while achieving high linearization accuracy through combined operation.
2Productivity
If power amplifiers operate at higher power levels, then productivity increases, but object-generated harmful factors worsen due to increased distortion from transistor saturation
Solution Approach 1:
The predistortion circuits apply compensating distortion to the input signal before it reaches the power amplifier. By pre-distorting the signal in the opposite direction of the expected amplifier distortion, the system enables operation at higher power levels while maintaining linear output, effectively preventing distortion before it occurs.
Solution Approach 2:
The system uses feedback from the power amplifier output to continuously adjust and optimize the predistortion parameters. This closed-loop control ensures that the predistortion compensation remains accurate even as operating conditions change, allowing sustained high-power operation with minimal distortion.
3Manufacturing precision
If adaptive digital predistortion circuits are added, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The adaptive predistortion functionality is segmented into distinct circuits with specific functions: one for memoryless effects and another for memory effects. This segmentation prevents the need for a single overly complex adaptive system, allowing each circuit to be independently optimized and controlled.
Solution Approach 2:
The predistortion circuits are designed to work together as a unified system that handles multiple types of distortion mechanisms simultaneously. The memoryless and memory effect circuits complement each other, creating a universal solution that addresses both short-term and long-term distortion without requiring separate specialized systems.
Data Source
AI summary
Digital predistortion system, methods and circuitry for adapting a predistortion system linearizing a non-linear element. The system is a multiply partitioned architecture that addresses long or “memory” effects, and separately addresses shorter duration effects. In a preferred method, the non-linear element is first modeled in software as a nonlinearity and a linearity in cascade form, preferably a Wiener model. The model is validated and adapted to minimize an observed error between the model and the non-linear element. The software model of the non-linear element is then used first to model a predistortion block that addresses short duration effects, and second to separately model a predistortion block that addresses longer duration effects. The models are software executable by an external processor in real time. Periodically the models are executed and used to update the adaptive parameters of the predistortion system without interrupting the system operation.