Doherty Amplifier Harmonic Resonance for Impedance Stability
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Solution Overview
Problem
The Doherty amplifier disclosed in Patent Literature 1 maintains infinite impedance for the second harmonic but fails to prevent changes in impedance for higher harmonics other than the second harmonic, leading to efficiency degradation.
Innovation Solution
The Doherty amplifier incorporates series and parallel resonant circuits tuned to specific higher harmonics, ensuring fixed impedance for the second and third harmonics by forming short-circuited and open ends at these frequencies, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If only a single type of resonant circuit is used to maintain impedance for one higher harmonic, then the impedance for that specific higher harmonic is maintained, but the impedance for other higher harmonics changes when load impedance changes
Solution Approach 1:
The patent divides the impedance control function into multiple segments by introducing separate resonant circuits for different higher harmonics. Specifically, a first parallel resonant circuit is dedicated to maintaining impedance for the first higher harmonic, while a second parallel resonant circuit handles the second higher harmonic. This segmentation allows each circuit to independently stabilize its designated harmonic without being affected by load impedance changes, thereby resolving the contradiction between maintaining stability for one harmonic and adapting to multiple harmonics.
Solution Approach 2:
The patent creates a multi-functional impedance control system where parallel resonant circuits serve multiple purposes. Each parallel resonant circuit not only maintains impedance for its designated higher harmonic but also contributes to the overall impedance stability of the system. The first parallel resonant circuit maintains impedance for the first higher harmonic while the second parallel resonant circuit maintains impedance for the second higher harmonic, collectively providing universal impedance stability across multiple harmonics and enabling the system to adapt to various load conditions.
2Adaptability or versatility
If the load impedance changes, then the operating conditions of the amplifier may adapt to different loads, but the impedance for higher harmonics changes causing degradation in operation efficiency
Solution Approach 1:
The patent applies preliminary anti-action by introducing parallel resonant circuits that preemptively counteract the harmful effect of load impedance changes on higher harmonics. Before load impedance changes can degrade operation efficiency through harmonic impedance variations, the resonant circuits are already in place to maintain stable impedance for each higher harmonic. The first parallel resonant circuit prevents impedance changes for the first higher harmonic, and the second parallel resonant circuit prevents impedance changes for the second higher harmonic, thereby preventing energy loss and maintaining high operation efficiency regardless of load adaptations.
3Reliability
If multiple parallel resonant circuits are added to maintain impedance for multiple higher harmonics, then impedance stability for multiple harmonics is achieved, but the device complexity increases
Solution Approach 1:
The patent merges the impedance control functions for multiple higher harmonics into a unified system architecture. The first parallel resonant circuit and the second parallel resonant circuit are integrated into the same amplifier system, sharing common components such as the amplifier stage and power supply. This merging approach allows multiple impedance control functions to coexist in a compact configuration, reducing the overall device complexity compared to having completely separate control systems for each harmonic while still achieving stable impedance for multiple higher harmonics.
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
Prevents impedance changes for the second and third harmonics, maintaining high efficiency by stabilizing operation despite load impedance variations.
Implementation Method 1
a first series resonant circuit connected between an output end of the carrier amplifier and a ground, and configured to resonate at the frequency of the first higher harmonic
Implementation Method 2
a second series resonant circuit connected between an output end of the peak amplifier and the ground, and configured to resonate at the frequency of the first higher harmonic
Implementation Method 3
a first parallel resonant circuit having an end connected to the output end of the carrier amplifier, and another end connected to the output end of the peak amplifier, the first parallel resonant circuit being configured to resonate at the frequency of the second higher harmonic
Implementation Method 4
a second parallel resonant circuit having an end connected to the output end of the peak amplifier and the other end of the first parallel resonant circuit, and another end electrically connected to a load, the second parallel resonant circuit being configured to resonate at the frequency of the second higher harmonic
Data Source
AI summary
A Doherty amplifier includes: a carrier amplifier to amplify a first high frequency signal having a first higher harmonic and a second higher harmonic; a peak amplifier to amplify a second high frequency signal having the first higher harmonic and the second higher harmonic; a first series resonant circuit connected between an output end of the carrier amplifier and a ground, and configured to resonate at the frequency of the first higher harmonic; a second series resonant circuit connected between an output end of the peak amplifier and the ground, and configured to resonate at the frequency of the first higher harmonic; a first parallel resonant circuit configured to resonate at the frequency of the second higher harmonic; and a second parallel resonant circuit configured to resonate at the frequency of the second higher harmonic.