Doherty Amplifier Output Network for Broadband Load Modulation
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Solution Overview
Problem
Conventional Doherty amplifiers face challenges in achieving a balance between efficiency, bandwidth, back-off power range, and circuit size due to their complex structure and large circuit size, which limits their ability to meet the increasing demands of wireless communication systems.
Innovation Solution
The proposed solution involves an output network for a Doherty amplifier comprising a combination node, a main output network, an auxiliary output network, and a merging matching network. The main and auxiliary output networks are designed with specific sub-network topologies and configurations to ensure impedance matching and efficient operation across different power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional Doherty amplifier structure is used, then efficiency is improved, but circuit size increases and bandwidth is limited
Solution Approach 1:
The output network is divided into multiple sub-networks (first sub-network, second sub-network, third sub-network, fourth sub-network) with different circuit topologies. Each sub-network handles specific impedance matching functions at different power levels, allowing the amplifier to maintain high efficiency across a wide bandwidth without requiring a large overall circuit structure.
Solution Approach 2:
The patent implements dynamic load modulation using variable impedance networks that change their electrical characteristics based on the operating power level. The main and auxiliary amplifiers dynamically share power across different operating ranges, with the output network adapting its impedance transformation ratio to maintain optimal efficiency at each power level while covering a wide bandwidth.
2Use of energy by moving object
If quarter-wavelength transmission line is used for load modulation, then efficiency is improved, but operating bandwidth becomes narrow
Solution Approach 1:
The patent changes the electrical parameters (impedance values, transformation ratios) of the output network sub-networks based on the operating power level. The impedance transformation ratios of different sub-networks are adjusted to maintain optimal load modulation across a wide frequency bandwidth, replacing the fixed quarter-wavelength transmission line approach with dynamically adjustable impedance networks.
3Adaptability or versatility
If bandwidth is increased by improving load modulation network, then operating bandwidth is improved, but amplifier size increases
Solution Approach 1:
The patent merges the load modulation function and impedance matching function into a single integrated output network structure. The multiple sub-networks are cascaded to simultaneously achieve load modulation across different power levels and broadband impedance matching, eliminating the need for separate broadband matching networks and reducing overall amplifier size.
Data Source
AI summary
Disclosed are an output network of a Doherty amplifier, a Doherty amplifier including the output network, and a design method of the Doherty amplifier. The output network includes a combination node, a main output network connected between an output port of the main amplifier and the combination node, an auxiliary output network connected between an output port of the auxiliary amplifier and the combination nod, and a merging matching network connected between the combination node and a radio frequency output port of the Doherty amplifier, where the merging matching network is configured for the node impedance at the combination node being a complex impedance, and the main output network and the auxiliary output network are configured for the node impedance matching with goal load impedances of the main amplifier and the auxiliary amplifier.