PCB Signal Trace Ground Plane EMI Reduction
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Solution Overview
Problem
Conventional printed circuit boards face challenges with signal quality and electromagnetic interference (EMI) due to longer current return paths and undesired magnetic fields, especially with high-speed signals, which increase impedance and signal attenuation, and are exacerbated by the coupling between adjacent signal traces.
Innovation Solution
The implementation of a printed circuit board design with a ground plane on the bottom surface and isolated power planes on the top surface, where conductive connections couple to the power planes across the signal trace without electrically connecting to it, allowing the signal trace to directly pass over a solid ground plane without splits, thereby reducing EMI and improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional two-layered PCB design with power traces and signal traces on the top layer and ground plane on the bottom layer is used, then the manufacturing cost is low, but the current return path becomes longer resulting in higher impedance and signal attenuation
Solution Approach 1:
The patent transitions from a conventional two-layered PCB to a multi-layered PCB design, adding intermediate layers between the top signal layer and bottom ground layer. This dimensional change in layer structure allows the signal trace to have a direct vertical return path to the ground plane through via plugs, eliminating the need for long horizontal return paths through splits in the ground plane.
2Adaptability or versatility
If the signal trace passes over splits in the ground plane to allow power transmission, then power transmission between adjacent power traces is enabled, but undesired magnetic fields are generated increasing EMI
Solution Approach 1:
The patent segments the ground plane into separate regions by introducing splits that isolate areas beneath adjacent power traces. This segmentation allows each power trace to have its own dedicated ground reference area, enabling independent power transmission paths while preventing magnetic field coupling between adjacent signal traces.
Solution Approach 2:
The patent introduces intermediate conductive layers and via plugs as mediators between the top signal layer and bottom ground layer. These intermediary elements provide direct vertical connection paths for current return, eliminating the need for current to flow horizontally through split regions, thus preventing undesired magnetic field generation.
3Reliability
If a multi-layered PCB is used to separate power, signal and ground planes in different layers, then signal quality improves and EMI is reduced, but manufacturing cost increases
Solution Approach 1:
The patent utilizes the vertical dimension by stacking multiple conductive layers at different heights, connected through via plugs. This three-dimensional arrangement allows signal traces on upper layers to have direct vertical return paths to ground planes on lower layers, achieving excellent signal quality and EMI reduction while maintaining a compact structure that is more cost-effective than alternative designs.
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 design achieves better signal quality and reduced EMI effects by eliminating the need for additional layers, thus lowering manufacturing costs and improving high-frequency signal transmission without significant signal insertion loss.
Implementation Method 1
A conductive connection along a first direction couples to the two power planes, across the signal trace without electrically connecting to the signal trace
Implementation Method 2
When signals, especially high-speed signals, are transmitted along the signal trace 112, however, the current return path of the high-speed signals not only remains under the signal trace 112, but also along the split 150 directly under the signal trace 112
Data Source
AI summary
A printed circuit board is disclosed. The printed circuit board comprises a substrate having a top surface and a bottom surface. A ground plane is on the bottom surface. A signal trace is on the top surface along a first direction. At least two isolated power planes are on the top surface adjacent to opposite sides of the signal trace, respectively. A conductive connection along a second direction couples to the two power planes, across the signal trace without electrically connecting to the signal trace, wherein the signal trace doesn't directly pass over any split of the ground plane.