PCB Differential Transmission Line Skew Compensation
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Solution Overview
Problem
Conventional differential transmission lines on printed circuit boards (PCBs) experience significant skew effects due to the need for vias to connect devices with mismatched polarities, leading to signal quality degradation from extra reflections and insertion losses.
Innovation Solution
A PCB design featuring a pair of differential transmission lines where one conductor has a curved middle section acting as a delay line, isolated from a buried trace by a ground layer, and via pins extending through cut-out regions, compensating for skew introduced by the cross-via structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If vias are added to connect devices with mismatched polarities, then device connectivity is achieved, but signal skew increases due to extra reflection and insertion loss
Solution Approach 1:
The patent applies asymmetry by making one transmission line conductor (the first conductor) longer than the other (the second conductor). The first conductor includes an additional curved section that increases its length, creating an asymmetric differential transmission line structure. This asymmetry compensates for the skew introduced by the via connections, allowing signal timing to be balanced between the two conductors despite the structural differences and via-induced delays.
2Reliability
If transmission line length is increased to compensate for skew, then signal timing is balanced, but transmission loss increases
Solution Approach 1:
The patent applies local quality by adding the curved section only to the first transmission line conductor where needed for skew compensation, rather than uniformly increasing the length of both conductors. The curved section is strategically placed in a localized area, allowing differential signal timing adjustment without proportionally increasing the total transmission path length and associated losses for both signal paths.
Data Source
AI summary
A PCB includes a PCB body at least including a first metal layer, a second metal layer, and a first ground layer sandwiched therebetween; and a pair of transmission lines including a first transmission line conductor and a second transmission line conductor. The first transmission line conductor is located in the first metal layer which has two straight line sections at its two ends and a curved line section at its middle, the second transmission line conductor has two straight line sections at its two ends which are located in the first metal layer and a cross-via structure at the middle which has a buried trace buried in the second metal layer, and the curved line section and the buried trace are isolated by the first ground layer. Skew effect of the differential transmission circuit is reduced, thereby improving the signal transmission quality and improve signal transmission speed.