Branch Line Coupler Amplifier Layout for Compact Load Modulation
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Solution Overview
Problem
Existing amplifier circuits, such as the Load Modulated Balanced Amplifier (LMBA), face challenges in downsizing due to the use of large distributed constant type branch line couplers with ¼ wavelength lines, which increase the overall size of the amplifier circuit.
Innovation Solution
The proposed amplifier circuit incorporates a branch line coupler with specific transmission line configurations, where the first characteristic impedance of the first and third transmission lines is higher than the reference impedance, and the second characteristic impedance of the second and fourth transmission lines is lower than the first characteristic impedance divided by √2. This configuration allows for a downsized branch line coupler and reduced variation in the load impedance of the control amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a distributed constant type branch line coupler with ¼ wavelength lines is used, then the amplifier circuit achieves proper signal combining and load modulation, but the circuit size increases
Solution Approach 1:
The patent changes the characteristic impedance parameters of the transmission lines in the branch line coupler. Specifically, it sets the first characteristic impedance higher than the reference impedance and the second characteristic impedance lower than the first characteristic impedance divided by √2. These parameter changes enable the coupler to achieve proper signal combining and load modulation functions while allowing for a more compact physical implementation, thus resolving the contradiction between reliability and circuit size.
2Area of stationary object
If the branch line coupler is downsized, then the amplifier circuit becomes more compact, but the load impedance variation of the control amplifier increases
Solution Approach 1:
The patent employs specific characteristic impedance parameter settings to maintain load impedance stability even in a downsized configuration. By setting the first characteristic impedance higher than the reference impedance and the second characteristic impedance lower than the first characteristic impedance divided by √2, the coupler maintains proper signal combining ratios and phase relationships, thereby stabilizing the load impedance seen by the control amplifier despite the reduced physical size.
Solution Approach 2:
The patent uses a composite structure in the branch line coupler with transmission lines having different characteristic impedances. This composite approach, where different impedance values are strategically assigned to different transmission lines, enables the coupler to achieve both compact size and stable load impedance characteristics by balancing the electrical lengths and impedance transformations within the structure.
3Area of stationary object
If the first characteristic impedance is increased and the second characteristic impedance is decreased, then the branch line coupler can be downsized, but the impedance matching becomes more challenging
Solution Approach 1:
The patent establishes specific parameter relationships for the characteristic impedances to enable downsizing while maintaining manufacturability. By defining the first characteristic impedance as higher than the reference impedance and the second characteristic impedance as lower than the first characteristic impedance divided by √2, the design provides clear fabrication targets that balance compactness with ease of implementation using standard transmission line technologies.
Data Source
AI summary
An amplifier circuit includes a first divider dividing an input signal into first and second signals, a control amplifier outputting a third signal, a second divider dividing the second signal into fourth and fifth signals, a first auxiliary amplifier outputting a sixth signal, a second auxiliary amplifier outputting a seventh signal, and a branch line coupler including first to fourth ends and first to fourth transmission lines. A first characteristic impedance at the center frequency of the first transmission line and the third transmission line is higher than a reference impedance, and a second characteristic impedance at the center frequency of the second transmission line and the fourth transmission line is lower than the first characteristic impedances/√2. An amplitude of a power of the seventh signal is larger than an amplitude of a power of the sixth signal.