PCB Stacking-Direction Differential Impedance Reduction
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Solution Overview
Problem
Existing printed circuit boards face challenges in reducing the differential impedance of differential transmission lines, as increasing the via diameter to reduce self-inductance makes it difficult to also decrease the center-to-center distance of the vias, thereby complicating the reduction of differential impedance.
Innovation Solution
A printed circuit board design featuring a stacking-direction differential transmission line with a differential signal via pair and conductor plate pairs that expand outward from the via rims, where the center of gravity of the conductor plates is located on the inner side of the via center of gravity, allowing for reduced self-inductance and increased mutual inductance, thereby reducing the differential impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the via diameter is increased to reduce self-inductance, then the self-inductance is reduced, but the center-to-center distance of the vias cannot be decreased, making it difficult to reduce differential impedance
Solution Approach 1:
The patent divides the via structure into multiple components: signal vias for differential signals and separate ground vias for grounding. This segmentation allows independent optimization of each via type, enabling the signal vias to be positioned closer together while ground vias provide the necessary electromagnetic shielding and reference plane, thus reducing differential impedance without compromising self-inductance management.
Solution Approach 2:
The patent introduces ground vias as intermediary elements between the differential signal vias. These ground vias act as mediators that provide electromagnetic shielding and establish a reference potential, enabling the signal vias to be positioned closer together (reducing center-to-center distance) while the ground vias manage the inductance effects through their shielding action.
2Adaptability or versatility
If the center-to-center distance of vias is decreased to reduce differential impedance, then the differential impedance is reduced, but the self-inductance increases
Solution Approach 1:
Ground vias are introduced as intermediary elements that mediate between the closely-spaced signal vias. These ground vias provide electromagnetic shielding that reduces the inductive coupling between adjacent signal vias, allowing the signal vias to be positioned closer together (reducing differential impedance) while the ground vias compensate for the increased self-inductance through their shielding effect.
Solution Approach 2:
The patent changes the configuration parameters of the via structure by introducing ground vias with specific positioning and dimensions. By adjusting the parameters of ground vias (such as their distance from signal vias and their diameter), the electromagnetic field distribution is modified to reduce inductive effects while maintaining the reduced center-to-center distance of signal vias for lower differential impedance.
3Volume of moving object
If high density mounting is implemented to reduce device size, then the device size is reduced, but the differential transmission line structure becomes more complex
Solution Approach 1:
The ground vias serve multiple functions simultaneously: they provide electromagnetic shielding for the differential signal vias, establish a reference ground plane, and contribute to impedance control. This multi-functionality allows the via structure to achieve high-density mounting with reduced device size while managing the complexity through unified ground via elements that perform multiple roles.
Solution Approach 2:
The patent optimizes the geometric parameters of the via structure (such as via diameter, spacing, and depth) to achieve high-density mounting. By carefully controlling these parameters, the differential transmission line structure can be compacted to reduce device size while maintaining acceptable performance, and the regular patterning of vias provides a systematic approach that manages structural 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
The design effectively reduces the differential impedance of the transmission line while maintaining stable impedance characteristics across a wide frequency range, ensuring low reflection and high transmission quality.
Implementation Method 1
reduced self-inductance and increased mutual inductance
Implementation Method 2
reduced self-inductance and increased mutual inductance
Data Source
AI summary
Provided are a printed circuit board configured to achieve reduction in impedance of a differential transmission line extending in a stacking direction, and an optical module. The printed circuit board includes a stacking-direction differential transmission line extending in the stacking direction, including: a differential signal via pair including a first signal via and a second signal via; and a plurality of conductor plate pairs each including a first conductor plate expanding outward from the first signal via, and a second conductor plate expanding outward from the second signal via. With respect to a perpendicular bisector of a center-of-gravity line segment connecting centers of gravity of the first and second signal vias, in each of the plurality of conductor plate pairs, centers of gravity of contours of the first and second conductor plates are located on inner sides of the centers of gravity.