Vehicle Shielded Cable Grounding to Mitigate EMI Loops
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Solution Overview
Problem
In-vehicle communication systems using coaxial cables are susceptible to ground loop problems, which cause performance degradation due to electromagnetic interference (EMI), particularly in applications with high data rates and long cable runs.
Innovation Solution
A communication system utilizing a shielded cable with a signal wire connected to both communication devices and a shield electrically coupled to their respective grounds, along with capacitors for AC coupling to ground planes, and wires connecting ground planes to the vehicle chassis at specific points to mitigate EMI effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If coaxial cables are used for in-vehicle communication, then susceptibility to in-band RE and noise is reduced, but ground loop problems occur causing performance degradation
Solution Approach 1:
The patent introduces a ground loop mitigation device as an intermediary component connected between the coaxial cable shield and the communication devices. This device acts as a mediator that blocks ground loop currents while maintaining the shielding effectiveness of the coaxial cable, thus resolving the contradiction between noise resistance and ground loop susceptibility
Solution Approach 2:
The ground loop mitigation device segments the ground path by introducing a break in the continuous conductive loop formed by the coaxial cable shield and communication device grounds. This segmentation prevents circulating ground loop currents while preserving the electrostatic shielding benefits of the coaxial structure
2Object-affected harmful factors
If shielded cable is used with shield connected to ground at both communication devices, then EMI protection is improved, but closed conductive loops are formed causing ground loop currents
Solution Approach 1:
The ground loop mitigation device serves as an intermediary element in the shield-to-ground connection path. It allows the shield to remain connected to ground for EMI protection while simultaneously blocking the formation of continuous conductive loops that would carry ground loop currents, thus resolving both requirements
3Object-affected harmful factors
If ground loop area is reduced, then EMI effects are attenuated, but system complexity increases due to additional grounding considerations
Solution Approach 1:
The ground loop mitigation device extracts or removes the harmful ground loop current component from the grounding system while preserving the essential ground connection for EMI protection. This extraction approach reduces EMI effects without requiring complete redesign of the grounding architecture, thus limiting the increase in system complexity
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
Reduces the area of ground loops and attenuates low-frequency EMI, thereby minimizing bit error rates and improving communication system performance.
Implementation Method 1
a shielded cable that communicatively connects the first communication device and the second communication device, the shielded cable having i) a signal wire that is electrically connected to the first communication device and the second communication device, and ii) a shield that is electrically coupled to the first ground and the second ground
Data Source
AI summary
A communication system in a vehicle includes a first communication device having a first ground, and a second communication device having a second ground. A shielded cable communicatively connects the first communication device and the second communication device. The shielded cable includes i) a signal wire that is electrically connected to the first communication device and the second communication device, and ii) a shield that is electrically coupled to the first ground and the second ground. A first wire electrically connects the first ground to a chassis of the vehicle at a first point. A second wire electrically connects the second ground to the chassis proximate to the first point to mitigate effects of electromagnetic interference (EMI) on the communication system.