RF Crossover Structure With Segmented Ground Shielding
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Solution Overview
Problem
Radio frequency (RF) circuits face undesired crossover coupling due to mutual capacitive coupling between RF signal paths, which can reduce the operating frequency range and affect circuit performance, and existing solutions that introduce a ground layer to mitigate this issue often lead to adverse capacitive coupling effects.
Innovation Solution
The implementation of a symmetrical crossing pattern in an integrated circuit with a ground return region and transmission lines separated by a fixed distance gap, where the transmission lines cross at a middle region with a segment on a different metal layer, and the use of a ground shield or local ground bumps to control coupling between the lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a ground layer is inserted between crossover paths to reduce mutual capacitive coupling, then crossover coupling is reduced, but capacitive coupling between RF signal paths and ground increases, reducing operating frequency range
Solution Approach 1:
The ground layer is segmented into isolated ground regions rather than a continuous layer. Each ground region is separated from adjacent signal paths by gaps, reducing the capacitive coupling area between signals and ground while maintaining isolation between crossing paths. This segmentation allows the ground to provide shielding without creating excessive capacitive loading that would limit operating frequency range.
Solution Approach 2:
The ground structure transitions from a uniform continuous layer to a non-uniform patterned structure with varying ground density. Ground regions are placed locally where needed for shielding between crossing paths, with gaps positioned strategically to minimize capacitive coupling to signal paths. This local optimization reduces overall capacitive loading while maintaining where needed.
2Area of stationary object
If transmission lines are placed close together to reduce area, then area is reduced, but mutual capacitive coupling increases
Solution Approach 1:
Ground regions act as intermediary shielding structures positioned between crossing transmission lines. These ground regions provide electromagnetic shielding that reduces mutual capacitive coupling between adjacent signal paths. The ground regions are strategically placed at crossover points where coupling would be strongest, effectively mediating the interaction between crossing signals while maintaining compact layout.
3Object-affected harmful factors
If a continuous ground layer is used to provide shielding, then shielding effectiveness is improved, but capacitive loading on signal paths increases
Solution Approach 1:
The continuous ground layer is divided into discrete segmented ground regions separated by gaps. This segmentation reduces the total capacitive area between ground and signal paths, thereby reducing capacitive loading and energy loss. The gaps are positioned to maintain shielding effectiveness between crossing paths while minimizing overall capacitive coupling to ground.
Solution Approach 2:
Rather than using a full continuous ground layer, the invention uses partial ground coverage with strategically placed ground regions. This partial action provides sufficient shielding to reduce crossover coupling while avoiding the excessive capacitive loading that would result from complete ground coverage. The ground is applied only where needed for shielding purposes.
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 effectively reduces crossover coupling and capacitive coupling to ground, enhancing the frequency range and performance of RF circuits by achieving improved isolation and maintaining desired characteristic impedance.
Implementation Method 1
crossover paths can induce undesired crossover coupling, primarily by way of mutual capacitive coupling, between RF signals conducted in the paths
Implementation Method 2
the first transmission line and the second transmission line cross at the middle region of the second transmission line to form a symmetrical crossing pattern with respect to the centerline
Data Source
AI summary
Systems, methods, and apparatus for reducing crossover coupling of two or more RF signals are described. In one case, a crossover structure is described where RF signals are routed through coplanar waveguides having a specific characteristic impedance and crossing at a central point of the crossover structure by way of a bridge. A ground shield having a geometry adapted to reduce the crossover coupling while minimally affecting capacitive coupling between the RF signals and the ground shield is introduced in-between a region comprising the central point. Further described is a multi-port rotary RF switch fitted with the crossover structure which allows substantially balanced electrical performance across all the operational states of the rotary RF switch at RF signal frequencies up to 40 GHz and beyond.