Rotary RF Switch Crossover Layout for Low Coupling at 50 GHz
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Solution Overview
Problem
Radio frequency (RF) circuits face issues with crossover coupling, leading to undesired capacitive coupling and performance degradation, particularly in multi-port rotary RF switches, where existing solutions like ground layers can reduce the operating frequency range and affect circuit performance.
Innovation Solution
A monolithically integrated N-port switch design with switchable conduction paths that cross at a central region of symmetry, utilizing peripheral and crossing paths with controlled impedance, and incorporating a ground shield and local ground bumps to minimize crossover coupling, ensuring low insertion loss and high isolation across a wide frequency range.
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 to ground increases and operating frequency range is reduced
Solution Approach 1:
The ground layer is segmented into discrete ground bumps positioned at specific locations beneath the crossover region, rather than providing continuous ground coverage. This segmentation reduces the total capacitive coupling area while maintaining isolation where most needed, preserving broadband operation.
Solution Approach 2:
Ground bumps are placed locally only in the crossover region where mutual coupling occurs, rather than providing uniform ground coverage throughout the signal path. This localized approach addresses the coupling problem at the critical interface while minimizing overall capacitive loading on the RF signals.
2Object-affected harmful factors
If crossover paths are designed to cross at a central region of symmetry, then isolation is improved, but device complexity increases
Solution Approach 1:
While the overall layout uses symmetry for balance, the individual switchable conduction paths employ asymmetric routing patterns that avoid direct crossing. The symmetric arrangement of multiple asymmetric paths creates a balanced structure with inherent isolation properties, reducing harmful coupling without requiring complex asymmetric designs.
Solution Approach 2:
The design moves the isolation function from the planar dimension to the vertical dimension by using stacked switchable conduction paths on different layers. This three-dimensional arrangement allows paths to cross in the planar view without actual electrical intersection, improving isolation while maintaining a relatively simple two-dimensional layout appearance.
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 solution effectively reduces crossover coupling, maintaining high isolation and low insertion loss across the frequency range from DC to 50 GHz, enhancing the performance of RF switches in both broadband and narrowband applications.
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
incorporating a ground shield and local ground bumps to reduce crossover coupling
Implementation Method 3
each switchable conduction path is configured to selectively operate in one of an ON state and an OFF state, the ON state providing a low impedance path between the respective two ports
Implementation Method 4
the OFF state providing a high impedance path between the respective two ports
Data Source
AI summary
Apparatus and arrangements 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. 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 50 GHz and beyond. A controller unit coupled to the RF switch can support a control interface to configure the rotary switch according to all possible distinct states of the rotary switch, or a subset thereof.