Doherty Amplifier Output Network for Wideband Load Modulation
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Solution Overview
Problem
Conventional Doherty amplifiers face challenges in achieving a balance between efficiency, bandwidth, and size due to their large circuit size and narrow operating bandwidth, which is exacerbated by the increasing complexity and number of radio frequency link units in wireless communication systems.
Innovation Solution
An output network for a Doherty amplifier is designed with a combination of main and auxiliary output networks and a merging matching network, featuring specific circuit topologies and impedance matching to ensure efficient operation across different power levels, while simplifying the structure and reducing size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional Doherty amplifier structure with quarter-wavelength transmission line is used, then load modulation is achieved, but operating bandwidth is narrow and circuit size is large
Solution Approach 1:
The output network is divided into multiple functional sub-networks: main output network, auxiliary output network, and merging matching network. Each sub-network performs a specific function (impedance transformation, load modulation, or combining), allowing independent optimization of each segment to achieve overall bandwidth enhancement without proportional size increase
Solution Approach 2:
The patent transforms the traditional quarter-wavelength transmission line structure into an LC circuit equivalent model with adjustable inductance and capacitance values. By optimizing these parameters, the network achieves broader frequency response while reducing physical dimensions compared to traditional transmission line implementations
2Loss of energy
If number of radio frequency link units is increased, then system efficiency is improved, but amplifier size and complexity increase
Solution Approach 1:
The main and auxiliary amplifier output networks are merged through the merging matching network at the combination node. This unified structure allows both amplifiers to contribute to system efficiency while sharing common impedance transformation and matching functions, reducing overall complexity compared to completely separate output stages
Solution Approach 2:
The merging matching network serves multiple functions simultaneously: it combines signals from both amplifiers, performs impedance transformation for both paths, and provides load modulation for both main and auxiliary amplifiers. This multi-functionality reduces the need for separate dedicated circuits for each function
3Adaptability or versatility
If conventional output network structure is used, then amplifier function is achieved, but back-off power range is limited
Solution Approach 1:
The output network is designed with dynamic impedance transformation capabilities through the LC circuit configurations. The inductors and capacitors are arranged to provide different effective impedance values at different power levels, enabling the amplifier to maintain optimal load conditions across a wider back-off power range
Solution Approach 2:
The merging matching network acts as an intermediary between the main and auxiliary output networks and the final load. It mediates the impedance transformation and signal combining processes, enabling extended back-off power range through controlled impedance variations without requiring complex individual output networks for each amplifier
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 of a Doherty amplifier including a main amplifier and an auxiliary amplifier, and 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 node; and a merging matching network connected between the combination node and a radio frequency output port of the Doherty amplifier; 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 being matching with the goal load impedances of the main amplifier and the auxiliary amplifier.