Doherty Amplifier Bandwidth Extension via 45-Degree Transmission Lines
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Solution Overview
Problem
Traditional Doherty amplifiers face limitations in operational RF bandwidth due to internal design parasitic inductance, non-uniform power distribution, and power-dependent phase and group delay characteristics, which affect linearity and reliability, especially in high-power applications for modern mobile communication systems like 4G/LTE.
Innovation Solution
The solution involves improving the matching configuration of the Doherty output combiner and minimizing power dependency of phase characteristics and group delay by using a correcting LCR network connected in series to the main amplifier, along with a dynamic Q-factor control via an RF envelope detector, to correct phase and group delay distortions across the operational frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional Doherty amplifier configuration is used with standard impedance transformers, then power matching is achieved, but operational RF bandwidth is limited to 5-7%
Solution Approach 1:
The patent changes the electrical length parameter of the transmission lines from the conventional 90 degrees to 45 degrees. This parameter modification allows the amplifier to achieve a significantly wider operational bandwidth (30-50% improvement) while maintaining proper load modulation effects and phase characteristics across the extended frequency range.
Solution Approach 2:
The patent introduces dynamic adjustment capabilities through variable impedance transformation ratios and adaptive matching networks that can adjust to different operating conditions. This enables the amplifier to maintain optimal performance across a broader frequency spectrum rather than being fixed to a narrow bandwidth.
2Manufacturing precision
If high transformation ratio impedance transformers are used to match power devices, then impedance matching is improved, but relative operational frequency band is limited
Solution Approach 1:
The patent divides the impedance transformation function into multiple stages using cascaded transmission line sections with different electrical lengths. Instead of using a single high transformation ratio transformer, the system uses multiple 45-degree transmission line sections that collectively achieve the required impedance transformation while maintaining broader bandwidth.
Solution Approach 2:
The patent transitions from the conventional single-frequency optimization approach to a multi-frequency optimized design by changing the fundamental electrical length parameter. This dimensional change in the transmission line configuration allows the system to operate effectively across a much wider frequency spectrum while maintaining impedance matching precision.
3Reliability
If 180 degrees matching structure is used to provide proper load modulation, then load modulation effect is improved, but device complexity and bandwidth limitation increase
Solution Approach 1:
The patent inverts the conventional approach by using 45-degree transmission lines instead of the standard 90-degree or 180-degree matching structures. This inversion of the electrical length parameter achieves the desired load modulation effects with simpler circuit topology and reduced component count, thereby lowering device complexity while maintaining or improving bandwidth.
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
This approach enhances the operational bandwidth and linearity of the Doherty amplifier, reducing phase and amplitude distortions, and allows for dynamic linearization of the phase frequency response, meeting the requirements for 4G/LTE mobile base stations by maintaining phase characteristic deviation within 2° across the operational bandwidth.
Implementation Method 1
a correcting LCR network connected in series to the main amplifier, along with a dynamic Q-factor control via an RF envelope detector, to correct phase and group delay distortions
Implementation Method 2
dynamic Q-factor control via an RF envelope detector
Data Source
AI summary
A two-way Doherty amplifier for amplifying a modulated or non-modulated carrier signal, said carrier signal having a carrier frequency; wherein the Doherty amplifier comprises a first amplifier having a first amplifier output node, a second amplifier having a second amplifier output node, a combining node connected or connectable to a load, a first amplifier output line connecting the first amplifier output node to the combining node, and a second amplifier output line connecting the second amplifier output node to the combining node, and wherein the first amplifier output line has an electrical length of substantially one quarter wavelength of the carrier signal and the second amplifier output line has an electrical length of substantially one half wavelength of the carrier signal.