FIR/IIR Predistortion for Power Amplifier Memory Effects
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Solution Overview
Problem
Power amplifiers in wireless transmitters suffer from non-linearity and memory effects, leading to inter-modulation distortion and phase distortion, particularly when amplifying high bandwidth signals, which existing predistortion techniques fail to adequately compensate for both short-term and long-term memory effects.
Innovation Solution
A transmitter system incorporating a predistortion sub-system with a memory-less component, a Finite Impulse Response (FIR) filter to address short-term memory effects, and an Infinite Impulse Response (IIR) filter to address long-term memory effects, along with an adaptation sub-system to configure these components adaptively, ensuring effective compensation for power amplifier non-linearity and memory effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single predistortion component is used, then the device complexity is reduced, but the ability to compensate for both short-term and long-term memory effects is insufficient
Solution Approach 1:
The predistortion sub-system is segmented into three distinct functional components: a memory-less predistortion component for non-linearity compensation, an FIR filter for short-term memory effects compensation, and an IIR filter for long-term memory effects compensation. Each component operates independently to address specific distortion types, enabling comprehensive compensation while maintaining modular architecture that manages complexity.
2Object-affected harmful factors
If only a memory-less predistortion component is used, then the device complexity is low, but the phase distortion from memory effects cannot be compensated
Solution Approach 1:
The harmful distortion effects are segmented into three categories: non-linearity (addressed by memory-less predistortion), short-term memory effects (addressed by FIR filter), and long-term memory effects (addressed by IIR filter). This segmentation allows each component to target specific distortion mechanisms without requiring a single complex solution.
Solution Approach 2:
The FIR and IIR filters act as intermediary components between the memory-less predistortion component and the power amplifier. These intermediary filters specifically address the memory effects that the memory-less component cannot handle, thereby eliminating phase distortion while maintaining the simplicity of the core predistortion function.
3Measurement precision
If FIR and IIR filters are both added to compensate for memory effects, then the compensation precision is improved, but the device complexity increases
Solution Approach 1:
Different filter types are assigned to different time-scale memory effects based on their local characteristics: FIR filters with finite impulse response are optimized for short-term memory effects (10-50 nanoseconds), while IIR filters with infinite impulse response are optimized for long-term memory effects (milliseconds or more). This local quality assignment achieves high precision compensation for each specific distortion type.
Data Source
AI summary
The present disclosure generally relates to predistortion that compensates for non-linearity of a power amplifier as well as short-term and long-term memory effects of the power amplifier. In one embodiment, a transmitter includes a power amplifier that amplifies a power amplifier input signal to provide a power amplifier output signal, a predistortion sub-system that effects predistortion of the power amplifier input signal to compensate for non-linearity of the power amplifier and memory effects of the power amplifier, and a adaptation sub-system that adaptively configures the predistortion sub-system. The predistortion sub-system includes a memory-less predistortion component that compensates for the non-linearity of the power amplifier, a Finite Impulse Response (FIR) filter that compensates for short-term memory effects of the power amplifier, and an Infinite Impulse Response (IIR) filter that compensates for long-term memory effects of the power amplifier.