Adaptive Digital Predistortion Modes for PA Linearity
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Solution Overview
Problem
Existing digital predistortion technologies struggle to maintain overall linearity of amplification systems while preserving high efficiency characteristics of nonlinear power amplifiers, such as Doherty power amplifiers used in mobile devices.
Innovation Solution
A transmitting device equipped with a multi-mode digital predistorter circuit that pre-compensates input baseband signals using various digital predistortion modes, selected based on feedback signals from the output, to optimize linearity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power amplifiers are biased to achieve high efficiency, then energy efficiency is improved, but signal quality deteriorates due to nonlinear operation
Solution Approach 1:
The digital predistorter applies preliminary compensation to the input baseband signal by pre-distorting it in opposite direction to the expected nonlinear distortion of the power amplifier. This anticipatory correction ensures that when the nonlinear amplifier processes the pre-distorted signal, the distortions cancel out, achieving linear output while maintaining high efficiency operation
Solution Approach 2:
The system employs feedback mechanisms where the output signal from the power amplifier is monitored and used to adjust the predistortion parameters. This closed-loop approach allows the digital predistorter to adapt to changing operating conditions and accurately compensate for nonlinear effects, maintaining signal quality across different power levels
2Reliability
If digital predistortion is applied to improve linearity, then signal quality is improved, but device complexity increases
Solution Approach 1:
The digital predistorter is divided into multiple independent kernels, each responsible for compensating specific types of nonlinear effects. This segmentation allows the system to apply only the necessary predistortion components for different operating conditions, reducing overall complexity while maintaining linearity performance
Solution Approach 2:
The system dynamically selects and switches between different predistortion modes (such as memoryless polynomial mode and memory polynomial mode) based on operating conditions like power level and signal characteristics. This dynamic adaptation enables the circuit to maintain optimal linearity performance without requiring all predistortion mechanisms to be active simultaneously, thereby managing complexity
Data Source
AI summary
Disclosed is a transmitting device, comprising, a multi-mode digital predistorter circuit configured to pre-compensate an input baseband signal in one of a plurality of digital predistortion modes according to a selection signal, a power amplifier configured to amplify the pre-compensated baseband signal and output the amplified baseband signal as an output signal of an allocated band, and a digital predistortion mode selector circuit configured to determine the one of the plurality of digital predistortion modes corresponding to the allocated band using a feedback signal obtained from the output signal, and set the multi-mode digital predistorter circuit to the one of the determined modes.