Sawtooth PCB Trace Skew Compensation for RFI Mitigation
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Solution Overview
Problem
Length mismatch between differential pair signals leads to skew, increasing common mode noise and radio frequency interference (RFI), which degrades Wi-Fi throughput and causes inter-symbol interference due to impedance mismatch and reflection.
Innovation Solution
Implementing a sawtooth structure with widened sections in differential pair trace routing on PCBs to match signal path lengths and smooth impedance, reducing skew and RFI while minimizing reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If skew compensation with meander routing is used, then length mismatch is compensated, but reflection increases due to impedance mismatch and discontinuity
Solution Approach 1:
The patent applies local quality by widening the trace only at specific locations where meander structures are present, rather than uniformly widening the entire trace. This localized impedance compensation targets the discontinuity points caused by meander routing, smoothing the impedance transition at jogged sections while maintaining the skew compensation benefits of meander routing.
Solution Approach 2:
The patent changes the physical parameter of trace width at specific locations to adjust impedance characteristics. By increasing the trace width at meander sections, the characteristic impedance is modified to compensate for the discontinuity introduced by the meander structure, thereby reducing reflection while maintaining path length matching.
2Object-generated harmful factors
If on-board EMI shielding is implemented, then RFI is reduced, but cost and footprint increase
Solution Approach 1:
The patent extracts the EMI shielding function from separate physical shielding structures and integrates it directly into the signal trace itself through widening. This eliminates the need for additional EMI shields while maintaining RFI reduction, as the widened trace acts as an inherent shielding structure.
Solution Approach 2:
The widened trace serves multiple functions simultaneously: it provides signal transmission, impedance matching, and EMI shielding. This multi-functionality consolidates what would traditionally require separate components into a single integrated structure, reducing overall device complexity.
3Object-generated harmful factors
If stripline routing is used, then EMI shielding is improved, but PCB thickness and cost increase
Solution Approach 1:
The patent employs asymmetric routing where one trace is widened at meander sections while the other remains narrow, creating intentional asymmetry to compensate for impedance discontinuity. This asymmetric approach provides EMI shielding benefits without requiring the symmetric enclosed structure of stripline routing, thereby avoiding increased PCB thickness.
Data Source
AI summary
Differential signal skew compensation techniques for radio frequency interference (RFI) mitigation with no reflection penalty and associated apparatus and methods. A differential pair of signal traces are formed on or in a PCB having at least two changes in direction, with a first signal trace having a first routing path defining a first length and a second signal trace adjacent to the first signal trace including one or more tuning structures that are configured such that the length of the second signal trace matches the first length. Segments of the first signal trace adjacent to the one or more tuning structures of the second signal trace are widened relative to other segments of the first signal trace. The tuning structures may comprise sawtooth structures, accordion structures and other serpentine or meander structures. The solution mitigates RFI without a reflection penalty.