Flexible Cable Mesh Ground Line Impedance Control
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Solution Overview
Problem
Flexible cables with reduced thickness for improved bending characteristics suffer from signal distortion due to increased capacitance, leading to undesired impedance mismatch and degraded high-frequency signal transmission.
Innovation Solution
The flexible cable design incorporates a micro-strip structure with a mesh-shaped ground line overlapping high-frequency signal lines and a plane-shaped ground line overlapping low-frequency signal lines, maintaining mechanical durability and heat radiation while preventing capacitance increase, thus ensuring 50-ohm impedance matching and improved signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the cable substrate and conductive line thickness are reduced to improve bending characteristics, then flexibility is improved, but capacitance increases causing signal distortion and impedance mismatch
Solution Approach 1:
The ground line is designed with different structures in different regions: a mesh-shaped first region overlapping high-frequency signal lines and a plane-shaped second region overlapping low-frequency signal lines. This local differentiation allows the mesh region to reduce capacitance for high-frequency signals while the plane region provides stable grounding for low-frequency signals, resolving the contradiction between flexibility and signal transmission quality.
2Shape
If the cable substrate thickness is reduced to achieve desired bending characteristics, then flexibility is improved, but impedance control becomes difficult leading to signal distortion
Solution Approach 1:
The ground line structure is changed from a conventional plane shape to a mesh shape in the first region overlapping high-frequency signal lines. This parameter change in ground line geometry reduces the overlapping area and capacitance, enabling impedance control (50-ohm matching) even when the cable substrate thickness is reduced for flexibility.
3Ease of operation
If the cable is designed with thin substrate for flexibility, then bending capability is improved, but heat radiation capability deteriorates
Solution Approach 1:
The cable uses a thin flexible substrate with a mesh-shaped ground line structure. The mesh configuration provides adequate heat dissipation surface area while maintaining the flexibility required for bending operations, resolving the contradiction between thin substrate requirements and heat radiation capability.
Data Source
AI summary
A flexible cable may include: a flexible substrate having a first surface and a second surface that are on opposite sides of the flexible substrate; a first conductive line formed on the first surface of the flexible substrate, and structured to transmit a signal having a first frequency; a second conductive line formed on the first surface of the flexible substrate, and structured to transmit a signal having a second frequency lower than the first frequency; and a ground line formed on the second surface of the flexible substrate, and comprising a first region overlapping the first conductive line and a second region overlapping the second conductive line. The first and second regions may have different shapes.