PCB Signal Line Layout With Open Metal Layer for Impedance Control
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Solution Overview
Problem
High-frequency signal transmission in display devices faces challenges due to increased skin effect and transmission loss, leading to reduced signal integrity and impedance mismatch, which are exacerbated by the limited planar space in printed circuit boards.
Innovation Solution
The design incorporates a printed circuit board with signal lines having specific line widths and mutual capacitances, including differential pairs and additional signal lines with narrower widths, and a metal layer with openings to optimize capacitance and impedance, reducing crosstalk and maintaining signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signal lines are formed with wider line widths to reduce impedance, then impedance matching is improved, but transmission loss increases due to increased skin effect
Solution Approach 1:
The patent introduces a vertical dimension by forming a metal layer beneath the signal lines in the lower substrate. This third-dimensional structure creates additional capacitance between the signal lines and the metal layer, allowing impedance control without increasing the planar line width, thereby avoiding increased skin effect and transmission loss.
Solution Approach 2:
The patent changes the capacitance parameter by introducing the metal layer with specific opening patterns. By controlling the area and position of openings in the metal layer, the capacitance between signal lines and the metal layer is adjusted, enabling impedance matching without modifying the signal line dimensions, thus avoiding increased transmission loss.
2Area of stationary object
If additional signal lines are added to increase planar space utilization, then space efficiency is improved, but crosstalk between signal lines increases
Solution Approach 1:
The metal layer with openings acts as an intermediary structure between the signal lines. By strategically placing openings, the patent reduces the capacitive coupling between adjacent signal lines, thereby minimizing crosstalk while maintaining high planar space utilization through the addition of multiple signal lines.
3Reliability
If signal line width is increased to reduce impedance, then impedance matching is improved, but near-end and far-end crosstalk increases
Solution Approach 1:
The patent moves the impedance control mechanism from the horizontal plane to the vertical dimension by introducing a metal layer beneath the signal lines. This allows impedance matching through vertical capacitance control without increasing the horizontal line width, thereby avoiding increased crosstalk between adjacent lines.
4Ease of manufacture
If the metal layer is made continuous to simplify structure, then manufacturing complexity is reduced, but capacitance control precision is worsened
Solution Approach 1:
The patent segments the metal layer by introducing openings at specific positions. This segmentation allows precise control of capacitance by adjusting the area and position of openings, while the overall structure remains relatively simple and manufacturable using standard PCB fabrication processes.
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 enhances signal transmission coefficients, reduces near-end and far-end crosstalk, and improves signal integrity by optimizing line widths and capacitances within the limited planar space, effectively addressing the skin effect and impedance issues.
Implementation Method 1
A pair of the signal lines may have a first mutual capacitance. A pair of the additional signal lines may have a second mutual capacitance. The pair of additional signal lines and the metal layer may have a third mutual capacitance.
Implementation Method 2
High-frequency signal transmission in display devices faces challenges due to increased skin effect and transmission loss
Data Source
AI summary
An embodiment of a printed circuit board includes a first insulating layer, a metal layer disposed above the first insulating layer, a second insulating layer disposed above the metal layer, and signal lines disposed above the second insulating layer, the signal lines extending in a first direction and having line widths in a second direction perpendicular to the first direction. The metal layer has open areas overlapping the signal lines in a third direction perpendicular to the first and second directions. In another embodiment, the open areas are replaced with metal meshes.