AC-Coupled Cable Ground Sheath for Low-Loss DC Blocking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In high-speed electrical channels, conventional AC-coupling capacitors cause significant signal performance degradation due to electrical losses, especially at higher data rates, and their mounting structures contribute to these issues.
Innovation Solution
A break in the ground path of a signal cable is created to provide DC blocking, eliminating the need for series-connected capacitors, with the break designed as an interdigitated or castellated shape to maintain effective high-pass filter properties, potentially located near cable ends for ruggedization and EMI shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC-coupling capacitors are used in series in the signal path, then DC blocking is achieved allowing receiver common mode voltage control, but signal performance degradation increases especially at higher data rates
Solution Approach 1:
The patent extracts the DC blocking function from the traditional series capacitor implementation and relocates it to a break in the ground path. By removing the capacitor from the signal path and placing the DC blocking mechanism in the ground return path, the solution eliminates the harmful electrical degradation while preserving the essential DC blocking capability needed for receiver common mode voltage control
Solution Approach 2:
The ground path break acts as an intermediary mechanism that provides DC blocking without requiring a physical capacitor in the signal path. The break in the ground sheath creates a high impedance path for DC signals while maintaining signal integrity for AC components, serving as a mediator between the need for DC isolation and the requirement for high-frequency signal transmission
2Reliability
If AC-coupling capacitors with mounting pads and PCB plated through holes are implemented, then DC blocking is provided, but electrical degradation and device complexity increase
Solution Approach 1:
The patent merges the DC blocking function with the ground path structure itself. Instead of adding separate capacitors, mounting pads, and plated through holes, the solution integrates the DC blocking mechanism directly into the ground sheath by creating a break in its continuity. This consolidation eliminates multiple discrete components and their associated mounting structures, reducing overall device complexity while maintaining the essential DC blocking function
3Reliability
If conventional AC-coupling capacitors are used on surrogate mounting PCBs, then DC blocking is achieved, but signal performance and PCB space efficiency deteriorate
Solution Approach 1:
The patent extracts the DC blocking function from the PCB-mounted capacitor implementation and relocates it to the cable's ground path. By removing the capacitor from the PCB assembly and implementing the DC blocking mechanism within the cable structure itself, the solution eliminates the need for additional PCB real estate dedicated to capacitor mounting while preserving the essential DC blocking capability
Solution Approach 2:
The ground sheath structure serves multiple functions: it provides electromagnetic shielding, maintains cable structural integrity, and now also provides DC blocking through the intentional break. This multi-functionality eliminates the need for separate DC blocking components on the PCB, optimizing space utilization while maintaining comprehensive cable functionality
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 signal degradation, lowers material costs by eliminating discrete capacitors, and frees up PCB space while maintaining low-frequency performance and high-frequency signal integrity.
Implementation Method 1
the break in the ground path has an associated capacitance to ground of the signal conductor through the insulation of the cable
Implementation Method 2
the transmitter (TX) and receiver (RX) devices are often DC isolated from each other using AC-coupling capacitors. Conventional technologies utilize a capacitor connected in series in the signal path to serve as a DC blocker
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.