Multi-Path Amplifier Input Network for Wider RF Bandwidth
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Solution Overview
Problem
Doherty power amplifier architectures face limitations in RF bandwidth, linearity, and AM-PM distortion, particularly at higher power levels and in millimeter wave frequencies, due to constraints in combiner devices and amplifier classes, which restrict their applicability in modern communication technologies like 5G.
Innovation Solution
A method for designing a multi-path amplifier involving an input network stage with analog processing modules, such as attenuators, differential phase shifters, and hybrid couplers, which are not user-adjustable, is connected to amplifier branches to optimize efficiency by compensating for imperfections in hardware prototypes through extensive empirical testing and frequency-domain equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Doherty power amplifier architectures are used to improve efficiency, then power efficiency is improved, but RF bandwidth is limited
Solution Approach 1:
The amplifier is divided into multiple parallel paths (main path and peaking paths) with different amplifier branches. Each branch can be independently optimized for specific frequency ranges, allowing the overall system to maintain high efficiency across a broader RF bandwidth by selectively activating appropriate branches.
Solution Approach 2:
The patent extends the traditional two-branch Doherty architecture into multi-path configurations with multiple peaking amplifiers. This dimensional expansion allows for broader bandwidth coverage by distributing signal processing across multiple parallel channels, each contributing to different portions of the frequency spectrum.
2Use of energy by moving object
If Class C biased peaking amplifiers are used to improve efficiency, then power efficiency is improved, but linearity deteriorates due to AM-PM distortion
Solution Approach 1:
Different amplifier branches are assigned different bias conditions and operating classes tailored to their specific functions. The main amplifier operates in one regime while peaking amplifiers operate in different regimes, allowing each component to optimize its local performance characteristics for either efficiency or linearity depending on its role in the signal envelope.
Solution Approach 2:
The input network stage acts as an intermediary that pre-processes and conditions the signal before it reaches the amplifier branches. This intermediate processing stage compensates for non-linearities and prepares the signal in a way that reduces AM-PM distortion effects in the subsequent high-efficiency Class C biased peaking amplifiers.
3Power
If combiner devices are used to combine output power, then power combining is achieved, but RF bandwidth is constrained
Solution Approach 1:
Instead of using a single broadband combiner, the patent employs multiple combiners in parallel, each optimized for specific frequency ranges or path combinations. This segmentation allows the system to maintain high output power across a broader overall bandwidth by routing different frequency components through appropriate combiner paths.
4Reliability
If pre-distortion input circuitry is added to improve linearity, then linearity is improved, but device complexity increases
Solution Approach 1:
The linearity improvement functions are merged into the existing input network stage that is already part of the multi-path architecture. Rather than adding separate pre-distortion circuitry, the input network is designed to perform both signal distribution and linearity compensation functions simultaneously, reducing overall device complexity.
Data Source
Figure 1~2
AI summary
A design method for designing a multi-path amplifier (10) involves connecting an amplifier stage having at least two amplifier branches to a combiner stage (6); feeding a plurality of testing signals with one or more of a plurality of sweeping variables to the amplifier stage; measuring output signals at the output of the combiner stage depending on the plurality of testing signals; designing a structure of an input network stage (2) for the amplifier stage on the basis of the measured output signals; and combining the designed input network stage with the amplifier stage to create an efficiency-optimised multi-path amplifier.