Doherty Power Amplifier Resonator Circuit for Wider Bandwidth
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Solution Overview
Problem
Traditional Doherty power amplifiers have a narrowband characteristic, limiting their bandwidth and efficiency, especially when using high-power gallium nitride (GaN) components, which often require operation in the traditional Doherty circuit structure, necessitating a redesign for improved performance across multiple frequency bands and operating modes.
Innovation Solution
A redesigned Doherty power amplifier circuit incorporating a series resonator circuit that appears inductive at higher frequencies, capacitive at lower frequencies, and has zero impedance at the central frequency, combined with a combiner featuring λ/4 impedance conversion lines and offset lines, to counteract reactance and enhance load pulling effects across a wider 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 traditional single λ/4 impedance conversion line is segmented into multiple sections with different characteristic impedances. The first λ/4 impedance conversion line has characteristic impedance Z01, the second has Z02, and the third has Z03, where Z01 ≠ Z02 ≠ Z03. This segmentation allows each section to contribute differently to the overall impedance transformation, enabling broadband operation while maintaining the high efficiency characteristics of the Doherty structure.
2Power
If GaN components are used in the traditional Doherty circuit structure, then high power output is achieved, but the circuit cannot operate in inverted Doherty structure
Solution Approach 1:
The redesigned Doherty circuit structure with multiple λ/4 impedance conversion lines creates a universal platform that can accommodate both traditional Doherty operation and inverted Doherty operation. The multi-section impedance transformation network provides the flexibility to support GaN components in either configuration, making the circuit structure compatible with different operational modes while maintaining high power output capability.
3Adaptability or versatility
If the Doherty circuit is redesigned for improved bandwidth, then broadband performance is enhanced, but the high efficiency characteristic may be compromised
Solution Approach 1:
The characteristic impedances of the λ/4 impedance conversion lines are carefully selected and optimized to maintain the fundamental Doherty operating principles across a wide bandwidth. By adjusting the impedance parameters Z01, Z02, and Z03 of the three λ/4 lines, the circuit achieves broadband operation while preserving the load modulation mechanism that enables high efficiency. The parameter optimization ensures that the efficiency characteristic is maintained across the extended frequency 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
The redesign significantly improves the broadband performance of the Doherty power amplifier, enabling efficient operation across multiple frequency bands and modes, reducing production and operating costs while maintaining high efficiency.
Implementation Method 1
a series resonator circuit arranged between the carrier amplifier branch and the combiner, and 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
Implementation Method 2
the combiner comprises a first λ/4 impendence conversion line with a characteristic impendence equal to 50 ohms, a second λ/4 impendence conversion line with a characteristic impendence equal to ohms, and a first load with a resistance equal to 50 ohms
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A Doherty power amplifier circuit comprises: a power divider (1), a carrier amplifier subcircuit (2), a combiner (3), and a peaking amplifier subcircuit (4), wherein a series resonance circuit (5) is disposed between the carrier amplifier subcircuit (2) and the combiner (3). 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.