Switchable Multiband Doherty Amplifier Without Digital Pre-Distortion
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Solution Overview
Problem
Doherty power amplifiers have limited optimal operating bands and require accurate phase control for high performance, which is challenging for modern communication standards like 4G/5G and Wi-Fi, especially with high peak-to-average power ratios, and often rely on digital pre-distortion techniques that degrade energy efficiency.
Innovation Solution
A Doherty amplifier design with a switchable high-band and low-band amplification pathway, using LDMOS transistors and tunable resonant networks for impedance matching, which allows for automatic selection of amplification pathways based on carrier frequency, eliminating the need for digital pre-distortion and enhancing frequency band coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital pre-distortion techniques are used to maintain linearity over the whole frequency band, then linearity is improved, but energy efficiency deteriorates
Solution Approach 1:
The frequency band is segmented into multiple bands (first frequency band and second frequency band), each handled by dedicated amplification pathways with band-specific impedance matching networks. This segmentation allows each pathway to be optimized for its specific band without requiring digital pre-distortion across the entire band, thereby maintaining linearity while improving energy efficiency.
2Adaptability or versatility
If a single amplification pathway is used to cover a wide frequency range, then frequency band coverage is improved, but performance (efficiency and linearity) deteriorates
Solution Approach 1:
The amplifier employs dynamic band selection through a switch that routes signals to different amplification pathways based on the detected carrier frequency. The system dynamically adapts its configuration to match the operating band, ensuring optimal performance for each frequency range while maintaining wide overall coverage.
Solution Approach 2:
Each amplification pathway is designed with local optimization for its specific frequency band, including band-specific impedance matching networks tuned to the characteristics of that band. This local quality approach ensures that each pathway delivers high performance for its designated band, and the switch enables seamless transitions between bands.
3Manufacturing precision
If the power level is lowered from the saturation point to operate in the linear zone, then linearity is improved, but efficiency deteriorates
Solution Approach 1:
The impedance matching networks are preliminarily tuned and optimized for each frequency band before signal amplification occurs. By pre-configuring the matching networks to present optimal impedance conditions for each band, the amplifiers can operate closer to saturation while maintaining linearity, thereby improving efficiency without sacrificing linearity performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves high efficiency and linearity over a broader frequency range (1.7-2.7 GHz) without digital pre-distortion, maintaining power-added efficiency and linearity performance, thus addressing the limitations of prior Doherty amplifiers.
Implementation Method 1
tunable resonant networks for impedance matching
Implementation Method 2
using LDMOS transistors
Data Source
AI summary
A Doherty amplifier includes: an input port; a pre-amplification stage; and at least one output port. The Doherty amplifier further includes: a high-band amplification pathway; a low-band amplification pathway; the high-band amplification pathway (VAHB) and the low-band amplification pathway each having a main amplifier, an auxiliary amplifier, and an output impedance matching network. A common network is connected to the high-band amplification pathway and to the low-band amplification pathway, the common network having a switch configured to selectively activate the high-band amplification pathway or the low-band amplification pathway. An intermediate impedance matching network is distributed between the common network, the high-band amplification pathway and the low-band amplification pathway.