PCB Signal Transmission Structure With Ground Notches for Impedance Control
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Solution Overview
Problem
In high-speed and high-frequency signal transmission scenarios, the low characteristic impedance of signal transmission lines, often due to limitations in board-making processes and dielectric materials, leads to increased signal reflection and reduced transmission quality.
Innovation Solution
The proposed signal transmission structure incorporates a reference ground layer with spacing grooves and notches to reduce the coupling area per unit length, thereby increasing the characteristic impedance and optimizing impedance control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the characteristic impedance of signal transmission lines is increased by using a low-Dk material or increasing the distance between the signal line and reference plane, then the impedance control is improved, but the design area is increased which reduces space utilization
Solution Approach 1:
The reference ground layer is segmented by introducing notches that divide the continuous ground plane into discrete sections. This segmentation reduces the coupling area between adjacent signal lines and the reference ground, thereby reducing capacitance per unit length and increasing characteristic impedance without requiring additional space or material changes.
Solution Approach 2:
The notches are strategically positioned only in specific regions where impedance control is needed, creating local modifications to the ground layer. This allows precise control of capacitance in critical areas while maintaining standard design elsewhere, optimizing space utilization without compromising overall impedance control.
2Reliability
If the characteristic impedance is too low to match impedance of transmitting end and receiving end, then signal reflection is increased and signal transmission return loss is increased, but the board-making process and dielectric materials have limitations that make it difficult to achieve higher impedance
Solution Approach 1:
The ground layer is divided into segmented regions through notches, which reduces parasitic capacitance between signal lines and the reference plane. This segmentation approach achieves higher characteristic impedance (matching transmitting and receiving end impedance) without requiring changes to dielectric materials or complex board-making processes.
Solution Approach 2:
The notches modify the electrical parameters of the transmission line by reducing the coupling area, thereby changing the capacitance per unit length. This parameter change increases the characteristic impedance to match impedance requirements, improving signal transmission quality without complicating manufacturing.
3Reliability
If spacing grooves and notches are introduced to reduce coupling area per unit length, then characteristic impedance is increased, but the structure complexity is increased
Solution Approach 1:
The ground layer is segmented using notches that are integrated into the existing PCB fabrication process. While this creates a more complex ground pattern, the segmentation is achieved through standard manufacturing techniques, and the resulting impedance control benefits outweigh the moderate increase in structural complexity.
Solution Approach 2:
The notches and spacing grooves are introduced only in specific locations where impedance control is critical, rather than throughout the entire PCB. This localized approach minimizes the overall structural complexity while achieving the necessary characteristic impedance in key signal transmission areas.
Data Source
AI summary
A signal transmission structure, an electronic device, and a PCB. The signal transmission structure includes a reference ground layer and a signal layer disposed above the reference ground layer. The signal layer includes a plurality of signal transmission lines are disposed in parallel along a line width direction having gaps therebetween. The reference ground layer includes a first reference area, and the first reference area is an orthographic projection area, at the reference ground layer, of two of the plurality of signal transmission lines and a gap between the two signal transmission lines. The first reference area is provided with a plurality of notches, and the plurality of notches is located on an orthographic projection, in the first reference area, of the two signal transmission lines, and the notches are distributed in an array at intervals along a line length direction of the signal transmission lines.