AC-Coupled Cable Sheath Structure for Low-Loss DC Isolation
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Solution Overview
Problem
Conventional AC-coupling capacitors in high-speed electrical channels cause significant electrical degradation due to their mounting pads and plated through holes, which become more pronounced at higher data rates, and are costly and occupy valuable PCB space.
Innovation Solution
Implementing a break in the ground path of the cable sheath to provide DC blocking, using interdigitated or castellated shapes to create a high-pass filter effect, eliminating the need for discrete capacitors and reducing signal degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC-coupling capacitors are used in series in the signal path, then DC isolation is achieved, but electrical degradation of signal performance occurs
Solution Approach 1:
The patent extracts the DC blocking function from the discrete capacitor component and integrates it into the cable sheath structure itself. The ground path is interrupted at specific points within the sheath, creating inherent AC coupling capability without requiring external capacitors. This eliminates the harmful effects of discrete capacitors while preserving the necessary DC isolation function.
Solution Approach 2:
The patent merges the DC blocking function with the cable sheath structure by creating interruptions in the ground path. The sheath simultaneously provides mechanical protection, electromagnetic shielding, and DC blocking functionality. This integration eliminates the need for separate AC-coupling capacitors and their associated mounting infrastructure.
2Reliability
If AC-coupling capacitors with mounting pads and plated through holes are used, then DC blocking is achieved, but PCB space is occupied and manufacturing complexity increases
Solution Approach 1:
The patent combines multiple functions (mechanical protection, electromagnetic shielding, and DC blocking) into the cable sheath structure. The ground path interruptions are created directly within the sheath during manufacturing, eliminating the need for separate capacitors, mounting pads, and plated through holes on the PCB.
Solution Approach 2:
The patent removes the DC blocking function from the PCB assembly and relocates it to the cable sheath structure. This extraction eliminates the need for discrete capacitor components and their associated PCB real estate, simplifying both the bill of materials and the manufacturing process.
3Reliability
If discrete AC-coupling capacitors are used, then AC signal propagation is enabled, but BOM costs increase
Solution Approach 1:
The patent integrates the AC coupling functionality directly into the cable sheath structure through ground path interruptions. This eliminates the need for discrete capacitor components in the bill of materials, as the sheath itself provides the necessary AC signal coupling while blocking DC.
Solution Approach 2:
The cable sheath structure provides its own AC coupling capability through the ground path interruptions, eliminating the need for external AC-coupling components. The sheath serves multiple functions simultaneously, making the system more cost-effective and easier to manufacture.
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 approach reduces electrical degradation, lowers BOM costs, and frees up PCB space by eliminating the need for discrete capacitors while maintaining effective AC signal propagation.
Implementation Method 1
the conductive layer comprises a first portion extending in a first direction along the cable and a second portion extending in a second direction, opposite the first direction, along the cable and further wherein the first and second portions of the conductive layer are separated from each other by a gap, the gap being dimensioned to provide a determined amount of capacitance in series in the ground sheath
Data Source
AI summary
A signal cable for an AC-coupled link, may include: a signal conductor; a dielectric surrounding the signal conductor; and a ground sheath having a conductive layer disposed at least partially around the conductor such that the dielectric is positioned between the ground sheath and the signal conductor, wherein the conductive layer comprises a first portion extending in a first direction along the cable and a second portion extending in a second direction, opposite the first direction, along the cable and further wherein the first and second portions of the conductive layer are separated from each other by a gap, the gap being dimensioned to provide a determined amount of capacitance in series in the ground sheath. The gap may form a complete separation between the first and second portions of the conductive layer.