Differential Trace Pair Impedance Control
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Solution Overview
Problem
Conventional differential trace pair systems face issues with common mode noise and signal integrity due to trace length mismatches, especially at high signal speeds beyond 25 Gbps, where serpentine region length matching approaches introduce impedance discontinuities and signal reflections.
Innovation Solution
The proposed solution involves a differential trace pair with a serpentine region that includes portions with varying widths and spacings, where the traces are parallel and spaced apart differently in different sections to maintain consistent impedance, minimizing impedance discontinuities and reducing insertion and return losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If serpentine region length matching is used to compensate for trace length mismatch, then common mode noise is reduced, but impedance discontinuities occur causing signal reflections and losses at high speeds
Solution Approach 1:
The patent applies local quality by varying the trace width specifically in the serpentine region where the trace transitions. The trace width is increased in the serpentine portion compared to the straight sections, which compensates for the inductance introduced by the serpentine geometry and maintains consistent impedance throughout the trace pair, thereby reducing reflections while still achieving length matching.
Solution Approach 2:
The patent changes the physical parameter of trace width in the serpentine region to optimize performance. By increasing the trace width in the serpentine portion, the characteristic impedance is adjusted to compensate for the additional inductance introduced by the serpentine geometry, maintaining impedance continuity and reducing signal reflections at high speeds.
2Object-affected harmful factors
If trace width is increased in serpentine region, then impedance continuity is improved, but trace routing flexibility is reduced
Solution Approach 1:
The patent applies local quality by varying the trace width specifically in the serpentine region where the trace transitions. The trace width is increased in the serpentine portion compared to the straight sections, which compensates for the inductance introduced by the serpentine geometry and maintains consistent impedance throughout the trace pair, thereby reducing reflections while still achieving length matching.
3Object-generated harmful factors
If differential trace pair spacing is increased, then crosstalk is reduced, but signal strength decreases
Solution Approach 1:
The patent changes the physical parameter of trace width in the serpentine region to optimize performance. By increasing the trace width in the serpentine portion, the characteristic impedance is adjusted to compensate for the additional inductance introduced by the serpentine geometry, maintaining impedance continuity and reducing signal reflections at high speeds.
Data Source
AI summary
A differential trace pair system includes a board having a first, a second, a third, and a fourth board structure member. A differential trace pair in the board includes a first differential trace extending between the first and the third board structure members, and a second differential trace extending between the second and the fourth board structure members. The differential trace pair includes a serpentine region that includes a first portion and a second portion where the first and the second differential traces have a first width, are substantially parallel, and spaced apart by a first differential trace pair spacing, and a third portion in which the second differential trace includes a second width that is greater than the first width, the first and second differential traces are substantially parallel and spaced apart by a second differential trace pair spacing that is greater than the first differential trace pair spacing.