Digital Power Amplifier Output Levels for Linearity at Back-Off
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Solution Overview
Problem
Conventional RF power amplifiers face inefficiencies due to high peak-to-average power ratio (PAPR) in modern communications standards, leading to low average operating efficiency and the need for significant back-off to prevent distortion, which limits their linearity and efficiency.
Innovation Solution
A digital power amplifier configuration with multiple activatable amplifiers and an output network that optimizes linearity by determining and adjusting output levels using a probability density function and genetic algorithms, allowing operation at different efficiencies and saturation powers to achieve improved linearity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional RF power amplifiers operate at high output power to achieve high efficiency, then efficiency is improved, but linearity deteriorates due to the need for back-off to accommodate signal peaks
Solution Approach 1:
The amplifier is divided into multiple parallel amplifiers (first amplifier, second amplifier, etc.), each capable of operating in saturation. By selectively activating specific amplifiers based on the instantaneous signal amplitude, the system achieves high efficiency (amplifiers operate at saturation) while maintaining linearity (only the required number of amplifiers are active for the current signal level).
Solution Approach 2:
The system dynamically adjusts the number of active amplifiers based on the instantaneous signal amplitude and probability density function. This dynamic configuration allows the amplifier to operate efficiently at high output power while maintaining linearity by activating additional amplifiers only when signal peaks occur, eliminating the need for continuous back-off.
2Manufacturing precision
If input power is reduced to prevent clipping and distortion, then linearity is improved, but efficiency deteriorates due to operating at back-off
Solution Approach 1:
Instead of reducing the input power to all amplifiers (back-off), the system segments the amplification function across multiple parallel amplifiers. Each amplifier operates at its full power capability in saturation, and the system achieves the required back-off effect by selectively activating only the necessary number of amplifiers based on signal peaks, thus maintaining both linearity and efficiency.
Solution Approach 2:
The system changes the operational parameters by allowing amplifiers to operate in saturation (full power) rather than at reduced power levels. The effective back-off is achieved not by reducing individual amplifier power but by controlling the number of active amplifiers, thus maintaining high efficiency while preventing clipping.
3Loss of energy
If multiple amplifiers are used to operate in saturation for high efficiency, then efficiency is improved, but device complexity increases
Solution Approach 1:
Multiple parallel amplifiers are merged through a combining network (such as a power combiner or transmission line network) that sums their outputs. This merging approach allows each amplifier to operate independently in saturation for high efficiency while presenting a unified output that maintains linearity, with the complexity managed through standard combining techniques.
Solution Approach 2:
The multiple amplifiers are designed with identical or similar characteristics, making them universal components that can be interchangeably activated. This multi-functionality allows the system to achieve complex efficient operation through simple replication of basic amplifier units, reducing design complexity through standardization.
Data Source
AI summary
A digital power amplifier for a signal, the digital power amplifier comprising:a first activatable amplifier;a second activatable amplifier; andan output network,wherein an output of the first amplifier and an output of the second amplifier are coupled to the output network, andwherein the amplifiers and/or the output network are configured such that four output levels are obtainable at an output of the output network, and said output levels are configured to optimise a linearity of the digital power amplifier for said signal.