Multilevel RF Power Amplifier Linearization During Bias Switching
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Solution Overview
Problem
Radio frequency (RF) power amplifier systems face challenges in achieving both high efficiency and high linearity, particularly due to nonlinearity introduced by dynamic switching of drain bias voltage among multiple supply levels, which leads to undesired signals and reduced performance metrics like Adjacent Channel Power Ratio (ACPR) and Error Vector Magnitude (EVM).
Innovation Solution
The implementation of a state-based digital predistortion (DPD) architecture and pulse cancellation techniques that correct for power supply input selection and transitions, ensuring the power amplifier gain is less sensitive to drain bias changes and minimizing disturbances by compensating for pulse-like variations in the RF output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If dynamic switching of drain bias voltage among multiple supply levels is used to improve efficiency, then power amplifier efficiency is improved, but linearity deteriorates due to nonlinearity introduced by switching
Solution Approach 1:
The patent applies preliminary action by using digital predistortion to pre-compensate the input signal before it reaches the power amplifier. The predistorter modifies the input signal in advance to counteract the expected nonlinear distortion from dynamic supply voltage switching, thereby maintaining linearity in the overall system while allowing efficient switching operation.
Solution Approach 2:
The patent implements feedback through a feedback path that monitors the output signal and feeds it back to the predistorter. This closed-loop feedback mechanism allows the system to continuously adjust the predistortion parameters based on actual output conditions, ensuring optimal linearity compensation despite variations in switching behavior and operating states.
2Use of energy by moving object
If discrete transitions among operating states are used to improve efficiency, then efficiency is improved, but undesired signals are generated reducing ACPR and EVM
Solution Approach 1:
The digital predistorter performs preliminary action by pre-compensating the input signal to counteract the distortion and undesired signal generation caused by discrete transitions among operating states. The predistortion is calculated in advance based on the known switching behavior, allowing the system to maintain signal quality while achieving efficient operation through state switching.
Solution Approach 2:
The feedback mechanism continuously monitors the output signal quality and adjusts the predistortion parameters to minimize undesired signals. This closed-loop control ensures that ACPR and EVM metrics are maintained within acceptable ranges despite the presence of discrete transitions and operating state changes.
3Use of energy by moving object
If multiple power supply levels are used to improve efficiency over wide output power range, then efficiency is improved, but complexity of power supply management increases
Solution Approach 1:
The patent applies segmentation by dividing the power supply system into multiple discrete voltage levels that can be independently controlled and selected. This segmentation allows the power amplifier to operate at different efficiency points corresponding to different output power ranges, with each voltage level optimized for specific operating conditions, thereby managing complexity through modular voltage level design.
Data Source
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AI summary
Circuits and methods for achieving high linearity, high efficiency power amplifiers are described. In some embodiments, switched-state RF power amplifier systems that employ digital predistortion (DPD) and pulse cancellation are provided.