PCB Differential Pair Width Tuning for Impedance Matching
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Solution Overview
Problem
The impedance mismatch in differential transmission lines on printed circuit boards (PCBs) occurs when the space between pairs of differential transmission lines changes, affecting signal integrity during bypassing voids or connecting to irregular structures.
Innovation Solution
The width of each differential transmission line is adjusted according to specific formulas (e.g., formula 11) to maintain constant impedance, ensuring signal integrity by changing the width in proportion to changes in the space between the lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the space between differential transmission lines is changed to bypass voids or connect to irregular structures, then the routing flexibility is improved, but the impedance consistency deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the width of differential transmission lines based on the space between them. When the space changes due to routing requirements, the width parameter is recalculated using specific formulas to maintain constant impedance. This allows the transmission lines to adapt to different spatial configurations while preserving impedance consistency, resolving the contradiction between routing flexibility and impedance consistency.
2Manufacturing precision
If the width of differential transmission lines is adjusted to maintain constant impedance, then the impedance consistency is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-establishing mathematical relationships and formulas that define how transmission line width should be adjusted based on spacing changes. During the design phase, these formulas are prepared so that during manufacturing, only simple width adjustments are needed rather than complex impedance calculations. This reduces manufacturing complexity while maintaining impedance consistency.
Data Source
AI summary
A printed circuit board includes an insulation layer and a signal layer attached to the insulation layer. The signal layer includes a pair of differential transmission lines. Width W of each of the differential transmission lines is changed according to change of space S between the differential transmission lines, based on the following formula:W=C1×H×(C2×H0.8W0+T)C3×ⅇC4×S0H-11-C3×ⅇC4×SH-1.25TIn above formula, C1=7.475, C2=5.98, C3=0.48, C4=−0.96, H is a thickness of the insulation layer, W0 is an original width of each of the differential transmission lines, and S0 is an original space between the differential transmission lines, and T is a thickness of each of the differential transmission lines.