Circuit Board Differential Trace Skew Reduction
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Solution Overview
Problem
Circuit boards with differential traces face issues of skew and differential to common-mode conversion when bent to accommodate a perpendicular mating direction, leading to transmission errors and increased size of cable harnesses.
Innovation Solution
A circuit board design with equal-length inner and outer trace portions and a ground conductor between them, connected via a via to a ground pattern, prevents electrical interaction and transmits differential signals as quasi-single ended signals, reducing skew and minimizing common-mode conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the differential traces are bent to L-shape to arrange the mating direction perpendicular to the extending direction, then the cable harness size is reduced, but skew occurs between the differential signal pair leading to transmission errors
Solution Approach 1:
The patent applies asymmetry by configuring the inner trace portion with a different shape than the outer trace portion. Specifically, the inner trace portion includes an inner bent portion that extends in a direction different from the extending direction of the outer trace portion, while the outer trace portion extends linearly. This asymmetric configuration allows both traces to have equal length despite the L-shaped bending, preventing skew while maintaining the compact perpendicular arrangement that reduces cable harness size.
2Reliability
If the inner trace is remodeled to have the same length as the outer trace to reduce skew, then skew occurrence is reduced, but the remodeled shape distorts differential signals to cause unnecessary mode conversion
Solution Approach 1:
The patent introduces a ground conductor portion as an intermediary element positioned between the inner trace portion and the outer trace portion. This ground conductor acts as a mediator that electrically shields the two traces from each other, preventing electromagnetic coupling and mode conversion. By inserting this intermediate ground reference, the patent achieves both equal-length trace configuration (reducing skew) and signal integrity maintenance (preventing differential to common-mode conversion).
Data Source
AI summary
A circuit board comprises at least a first wiring layer, a second wiring layer and a via. The first wiring layer is formed with a pair of first ends, a pair of second ends, a coupling portion, a pair of first trace portions and a pair of second trace portions. The coupling portion has a pair of first coupling points, a pair of second coupling points, an inner trace portion, an outer trace portion and a ground conductor portion. The inner trace portion has a length equal to a length of the outer trace portion. The ground conductor portion is arranged between the inner trace portion and the outer trace portion. The second wiring layer is formed with a ground pattern. The ground conductor portion is connected with the ground pattern through the via.