MMIC Air Bridge Coupler for Compact RF Signal Transfer
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Solution Overview
Problem
Conventional edge line couplers in MMICs occupy significant space and are sensitive to load impedance variations, while capacitive couplers provide limited coupling and erroneous signal sampling.
Innovation Solution
The use of a coupled line and multiple air bridges in a monolithic microwave integrated circuit (MMIC) to couple the transistor output signal to a load, where the air bridges electrically connect the drain of the transistor with a bond pad, allowing for efficient coupling of the RF signal across the entire transistor length without increasing the circuit's size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an edge line coupler is used to couple the transistor output signal to a load, then the coupling effect is improved, but the area occupied by the circuit increases substantially
Solution Approach 1:
The patent transitions from a planar edge-line coupler to a three-dimensional air bridge structure. The air bridge extends vertically above the substrate, creating a coupled line in the third dimension. This allows the coupled line to run parallel to the drain over an extended vertical path without occupying additional horizontal area, thereby achieving strong coupling effect while maintaining compact circuit footprint.
Solution Approach 2:
The air bridge structure nests the coupled line within the vertical space above the substrate. The coupled line is positioned in the air bridge region, utilizing the vertical dimension rather than horizontal space. This nesting approach allows the coupling structure to be embedded within the existing circuit layout without requiring additional lateral area.
2Area of stationary object
If a capacitive coupler is used to reduce circuit area, then the area is reduced, but the coupling effect becomes limited and sensitivity to load impedance variations increases
Solution Approach 1:
Instead of using a capacitive coupler that operates in the planar domain, the patent employs an air bridge structure that extends into the vertical dimension. The coupled line runs through the air bridge region, creating a distributed coupling structure with extended effective length. This three-dimensional configuration provides strong coupling effect comparable to edge-line couplers while maintaining the compact area advantage of capacitive couplers.
3Reliability
If a conventional edge line coupler is used, then directivity is improved, but the circuit becomes sensitive to load impedance variations and occupies substantial space
Solution Approach 1:
The air bridge coupled line extends vertically above the substrate, creating a distributed coupling structure with extended effective length. This three-dimensional configuration provides strong coupling and good directivity similar to conventional edge-line couplers, while the vertical arrangement allows the structure to be nested within the existing circuit footprint without requiring additional horizontal space.
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 improves coupling efficiency, reduces sensitivity to load impedance variations, and allows for accurate power output sensing, enhancing the operational reliability and compactness of the MMIC.
Implementation Method 1
multiple air bridges arranged parallel to one another and extending over the coupled line, where the air bridges and the coupled line provide coupling of the transistor output signal to a load
Data Source
AI summary
A monolithic microwave integrated circuit (MMIC) includes a transistor, coupled line and multiple air bridges. The coupled line is configured to output a coupled signal from the transistor, the coupled line running parallel to a drain of the transistor. The air bridges connect the drain of the transistor with a bond pad for outputting a transistor output signal, the bridges being arranged parallel to one another and extending over the coupled line. The air bridges and the coupled line effectively provide coupling of the transistor output signal to a load.