Doherty Amplifier Tuner for Back-Off Impedance Matching
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Solution Overview
Problem
Conventional Doherty amplifiers face challenges in achieving maximum efficiency at high impedance due to the fixed VSWR circle radius, making it difficult to find suitable transistors that match the required impedance for optimal performance at both small and high signal conditions.
Innovation Solution
A Doherty amplifier architecture with a tuner system, including a switch unit and a tunable microstrip, adjusts the load impedance of the main amplifier to match the optimal efficiency point at back-off power levels by varying the characteristic impedance of the microstrip, allowing the VSWR circle radius to be adjusted to reach the best efficiency point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the VSWR circle radius is fixed by hardware (characteristic impedances of microstrips), then the main amplifier load impedance is determined, but it is difficult to reach the best efficiency point at back-off power level
Solution Approach 1:
The patent applies the dynamics principle by transforming the fixed VSWR circle radius into an adjustable parameter. A tuner comprising a switchable microstrip is introduced to dynamically adjust the main amplifier load impedance, enabling the VSWR circle radius to be modified based on operating conditions. This allows the system to reach the best efficiency point at back-off power level by adjusting the load impedance to match optimal values, thereby resolving the contradiction between fixed hardware constraints and adaptability requirements.
2Manufacturing precision
If the characteristic impedances of microstrips are fixed, then the hardware structure is simplified, but the impedance matching for optimal efficiency cannot be achieved
Solution Approach 1:
The patent applies the parameter changes principle by introducing a tuner that modifies the electrical parameters (characteristic impedance and electrical length) of the transmission path to the main amplifier. The tuner comprises a switchable microstrip with controllable electrical length θ, allowing precise adjustment of load impedance to achieve optimal impedance matching for maximum efficiency. This parameter adjustment capability resolves the contradiction between manufacturing simplicity and impedance matching precision.
3Adaptability or versatility
If a fixed Doherty structure is used, then the design is simpler, but the transistor selection is limited due to fixed impedance requirements
Solution Approach 1:
The patent applies the dynamics principle by introducing an adjustable tuner that modifies the main amplifier load impedance based on operating conditions. This dynamic impedance adjustment expands the range of suitable transistors that can be used in the Doherty amplifier design, as different transistor types can now be accommodated by adjusting the load impedance to match their optimal efficiency points. The tuner includes a switchable microstrip with controllable electrical length, enabling flexible transistor selection without being constrained by fixed impedance requirements.
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 configuration enhances back-off power level efficiency, increases the transistor candidate pool for main amplifiers, and reduces the physical size and volume of radio units, enabling higher efficiency and flexibility in transistor selection.
Implementation Method 1
The main amplifier is connected to the output through an impedance-inverter, usually a quarter wavelength transmission line or an equivalent lumped network. To compensate the quarter wavelength transmission line, a quarter wavelength is added to the input of peak amplifier.
Implementation Method 2
at least one tuner connected, in series with the first microstrip, between the main amplifier and the peak amplifier. The at least one tuner comprises a third microstrip connected with the first microstrip in series, and a switch unit for controlling the third microstrip as a shunt.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A Doherty amplifier (300) is provided, it comprises: a main amplifier (301) and a peak amplifier (302); a first microstrip (303) with λ/4 electric length connected between the main amplifier and the peak amplifier; a second microstrip (304) with λ/4 electric length connected between a junction of outputs of the peak amplifier and the main amplifier, and an output terminal (306); at least a tuner (305) for adjusting radius of VSWR circle of the main amplifier and connected, in series with the first microstrip (303), between the main amplifier (301) and the peak amplifier (302) based on input signal power. The hack-off power level efficiency is increased by enlarge the VSWR radius with the new Doherty structure.