Doherty Power Amplifier Series Resonance for Load-Pull Bandwidth
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Solution Overview
Problem
Traditional Doherty power amplifier circuits have a narrowband characteristic, limiting their bandwidth and efficiency, particularly when using high-power gallium nitride (GaN) components, which cannot operate effectively in inverted Doherty circuits, necessitating a redesign for improved bandwidth.
Innovation Solution
A Doherty power amplifier circuit is redesigned with a series resonator circuit between the carrier amplifier branch and the combiner, which appears inductive at higher frequencies, capacitive at lower frequencies, and has zero impedance at the central frequency, counteracting the reactance introduced by the combiner to enhance load pulling and broaden the bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional Doherty circuit structure with λ/4 impedance conversion line is used, then high efficiency is achieved, but the available bandwidth is limited
Solution Approach 1:
The patent changes the electrical length parameter of the impedance conversion line from the traditional λ/4 (quarter wavelength) to a variable range of (n+1/4)λ where n=0,1,2,... This parameter modification allows the circuit to maintain high efficiency while achieving broader bandwidth operation by adjusting the electrical length to compensate for frequency variations across different operating bands
Solution Approach 2:
The patent introduces dynamic adjustability to the impedance conversion line's electrical length, allowing it to adapt to different frequency bands. This dynamic characteristic enables the amplifier to maintain optimal performance across multiple frequency ranges rather than being fixed to a single narrow bandwidth
2Adaptability or versatility
If an inverted Doherty circuit structure is used to achieve wider bandwidth, then bandwidth is improved, but high-power GaN components cannot operate effectively
Solution Approach 1:
The patent inverts the traditional Doherty structure by placing the series resonator circuit in the carrier amplifier branch rather than the peak amplifier branch, and positions the impedance conversion line in the carrier branch. This inverted configuration allows high-power GaN components to operate effectively while achieving wider bandwidth, solving both requirements simultaneously
3Adaptability or versatility
If the Doherty circuit is redesigned for improved bandwidth, then bandwidth is enhanced, but device complexity increases
Solution Approach 1:
The patent designs the series resonator circuit and impedance conversion line to serve multiple functions simultaneously: they provide bandwidth expansion, maintain impedance matching across frequency bands, and enable high-power component operation. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in overall circuit complexity despite the bandwidth enhancement
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 redesign significantly improves the broadband performance and efficiency of the Doherty power amplifier circuit, enabling it to operate in multiple frequency bands and modes, reducing production and operating costs while maintaining high efficiency.
Implementation Method 1
a series resonator circuit 5 is arranged between the carrier amplifier branch 2 and the combiner 3, and is configured to: appear inductive when an operating frequency of the Doherty power amplifier circuit is higher than a central frequency, appear capacitive when the operating frequency of the Doherty power amplifier circuit is lower than the central frequency, and have an impedance of 0 when the operating frequency of the Doherty power amplifier circuit is the central frequency
Data Source
AI summary
A Doherty power amplifier circuit comprises: a power divider, a carrier amplifier subcircuit, a combiner, and a peaking amplifier subcircuit, wherein a series resonance circuit is disposed between the carrier amplifier subcircuit and the combiner. In this way, reactance that would be introduced during an operating process of a conventional Doherty power amplifier circuit can be neutralized, such that a superior performance of the Doherty power amplifier circuit is ensured, and at the same time, a load-pull effect of the Doherty power amplifier circuit is improved to have a wider bandwidth, thereby realizing a communication device supporting operations in multiple frequency bands and multiple systems at the same time, and effectively lowering manufacturing and operation costs.