Flexible Printed Circuit Ground Loop EMI Shunting
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Solution Overview
Problem
Compact form factor electronic devices face challenges in managing electro-magnetic interference (EMI) due to space limitations, which can lead to sub-optimal EMI emission characteristics, necessitating innovative solutions for effective EMI management.
Innovation Solution
The use of flexible printed circuits with coverlay openings that expose ground planes to establish multiple ground loops through conductive foam or adhesives, allowing for enhanced ground plane connectivity and efficient shunting of EMI energy, where the ground loops can be strategically positioned to minimize length and maximize EMI emission management performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If flexible printed circuits are used in compact electronic devices, then space utilization is improved, but EMI emission management deteriorates due to limited space for ground loops
Solution Approach 1:
The ground plane is segmented into multiple exposed regions through coverlay openings, creating multiple separate ground loops rather than a single continuous path. This segmentation allows EMI shunting at multiple locations throughout the device, improving EMI management in compact spaces where a single ground loop would be too long or impractical.
Solution Approach 2:
The patent transitions from planar ground connections to three-dimensional ground loops by utilizing vertical spacing between the flexible printed circuit and other device components. Conductive materials fill the space between exposed ground planes, creating ground loops that extend in the Z-dimension, effectively using available volume rather than just surface area.
2Object-affected harmful factors
If ground loops are extended to improve EMI shunting, then EMI emission management is improved, but ground loop length increases which can reduce effectiveness
Solution Approach 1:
Ground loops are created locally near EMI sources rather than using a single distant ground reference. Multiple coverlay openings expose ground planes at different locations throughout the device, allowing each ground loop to be optimized for its specific local EMI environment, reducing the effective length and inductance of each ground path.
3Object-affected harmful factors
If multiple ground loops are created through coverlay openings, then EMI shunting is improved, but device complexity increases
Solution Approach 1:
Existing device components serve dual purposes: structural/functional elements simultaneously provide ground loop pathways for EMI management. Conductive materials that might otherwise be used for other purposes are utilized to create ground connections, and device housings or shields serve as ground references, eliminating the need for dedicated EMI management components.
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 configuration effectively manages EMI emissions by creating efficient ground loops that shunt EMI energy close to the source, enhancing overall EMI emission management in compact electronic devices, particularly in small form factor devices where space is limited.
Implementation Method 1
Electrical pathways are formed by conductive foam, conductive adhesives, and/or other conductive materials between the exposed ground planes and a device ground to establish multiple ground loops throughout the device that shunt EMI energy
Data Source
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AI summary
In an electronic device having a compact form factor, such as a head mounted display device, flexible printed circuits may be utilized to provide interconnects between EMI-generating peripheral components and other components in the device such as those populated on main circuit boards. Coverlays utilized to protect circuit traces and ground planes in the flexible printed circuits are configured with openings that can expose ground planes at various locations throughout the electronic device. Electrical pathways are formed by conductive foam, conductive adhesives, and/or other conductive materials between the exposed ground planes and a device ground to establish multiple ground loops throughout the device that shunt EMI energy that is generated by electronic components and circuits during device operation. The coverlay openings can be positioned on the flexible printed circuits so that the lengths of the ground loops are minimized to enhance overall EMI emission management performance.