Doherty Amplifier Phase Synthesis for Backoff Efficiency
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Solution Overview
Problem
The efficiency of existing Doherty amplifiers decreases due to inductive load modulation during the transition from a backoff point to saturation output, which is not effectively addressed by existing power amplifiers.
Innovation Solution
The Doherty amplifier design includes transmission lines with equal characteristic impedance and a phase difference that does not match the electrical length difference between the lines, allowing for different phase synthesis of signals, thereby reducing inductivity through capacitance generated by the phase difference during load modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a transmission line with equal electrical length difference to phase difference is used, then the amplifier can operate with high efficiency at saturation output, but efficiency decreases during load modulation from backoff point to saturation due to strong inductive load
Solution Approach 1:
The patent changes the electrical length parameters of the transmission lines. Specifically, it sets the electrical length of the first transmission line to 70-90 degrees and the second transmission line to 90-180 degrees, making their difference not equal to the phase difference between signals. This parameter modification transforms the load characteristic from strongly inductive to a more balanced state, maintaining efficiency across the operational range from backoff to saturation.
2Device complexity
If transmission lines with equal characteristic impedance are used, then signal distribution is simplified, but inductive load modulation causes efficiency loss during power transition
Solution Approach 1:
The patent modifies the electrical length parameter of the transmission lines while maintaining equal characteristic impedance. By setting the electrical length difference to be not equal to the phase difference, it changes the load modulation characteristic, reducing the harmful inductive effect and improving power-added efficiency during the transition from backoff to saturation output.
3Measurement precision
If the electrical length difference between transmission lines equals the phase difference between signals, then perfect phase synthesis is achieved at saturation, but inductive reactance increases during load modulation reducing efficiency
Solution Approach 1:
The patent deliberately sets the electrical length difference to be not equal to the phase difference. This parameter change accepts a slight compromise in perfect phase synthesis at saturation in exchange for significantly reducing the inductive reactance during load modulation, thereby maintaining higher efficiency across the entire operational range.
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 design enables the Doherty amplifier to maintain high efficiency from the backoff point to saturation output by minimizing inductive components, improving power-added efficiency.
Implementation Method 1
the phase difference between the first signal and the second signal is not equal to a difference in electrical length between the second transmission line and the first transmission line
Implementation Method 2
The inductivity generated during load modulation from the backoff point to the saturation output is reduced by capacitance generated in a load by the phase difference between the first signal and the second signal
Data Source
AI summary
A Doherty amplifier includes: a first amplifying element to amplify a first signal; a second amplifying element to amplify a second signal having a phase difference with the first signal; a first transmission line connected to an output terminal of the first amplifying element; and a second transmission line connected to an output terminal of the second amplifying element, wherein the first transmission line and the second transmission line are equal to each other in characteristic impedance, the phase difference between the first signal and the second signal is not equal to a difference in electrical length between the second transmission line and the first transmission line, and the first signal having passed through the first transmission line and the second signal having passed through the second transmission line are subjected to different phase synthesis.