Digital Predistortion with Level Tracking for RF Power Amplifier Linearity
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Solution Overview
Problem
Power amplifiers in RF communication systems exhibit nonlinear characteristics, leading to distortion, especially when operating near maximum output, and existing linearization techniques either compromise efficiency or linearity.
Innovation Solution
A linearization system that intentionally operates the power amplifier in a nonlinear mode using dynamic predistortion, where the predistortion coefficients are optimized based on both the input signal and the envelope tracking signal to mitigate nonlinear effects, allowing for efficient power management and extended component longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power amplifier operates near maximum output, then power efficiency is improved, but nonlinear distortion increases
Solution Approach 1:
The system applies predistortion to the input signal before amplification, intentionally introducing inverse nonlinear distortion that cancels out the amplifier's nonlinear effects. This preliminary counter-action allows the amplifier to operate efficiently near maximum output while maintaining linear output characteristics.
Solution Approach 2:
The system dynamically adjusts predistortion coefficients based on operating conditions, including the envelope tracking signal. By changing the predistortion parameters in real-time, the system optimizes the cancellation of nonlinear effects while maintaining high power efficiency across varying signal conditions.
2Use of energy by moving object
If aggressive shaping table is used for envelope tracking, then power efficiency is improved, but power amplifier linearity deteriorates
Solution Approach 1:
The system uses feedback from the envelope tracking signal and output monitoring to dynamically adjust predistortion coefficients. This closed-loop approach allows the system to maintain optimal linearity compensation even when using aggressive shaping tables for power efficiency, as the predistortion adapts to compensate for any linearity degradation.
Solution Approach 2:
The predistortion system is made dynamic by continuously adapting coefficients based on the envelope tracking signal and operating conditions. This dynamic adjustment allows the system to maintain linearity across varying power levels while benefiting from aggressive envelope tracking for improved power efficiency.
3Stability of the object's composition
If conservative shaping table is used for envelope tracking, then power amplifier linearity is improved, but power efficiency deteriorates
Solution Approach 1:
The system applies predistortion in advance to the input signal, preparing the signal to compensate for expected nonlinear effects before amplification occurs. This preliminary action allows the use of more conservative envelope tracking approaches that prioritize linearity, while the predistortion ensures power efficiency is maintained through optimized amplification operation.
Data Source
AI summary
Disclosed are systems, devices, modules, methods, and other implementations, including a method for digital predistortion that includes receiving, by a digital predistorter, a first signal that depends on amplitude variations based on an input signal, u, with the variations of the first signal corresponding to time variations in non-linear characteristics of a transmit chain that includes a power amplifier. The method further includes receiving, by the digital predistorter, the input signal u, generating, by the digital predistorter, based at least in part on signals comprising the input signal u and the first signal, a digitally predistorted signal v to mitigate the non-linear behavior of the transmit chain, and providing the predistorted signal v to the transmit chain.