Differential Pair Crossover Routing for Cross Talk Reduction
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Solution Overview
Problem
High-density integrated circuits face signal cross talk noise issues due to interference between parallel routed signal conductors, affecting signal quality and timing, particularly in high-speed applications.
Innovation Solution
The implementation of differential pair bus lines that change location relative to aggressor bus lines through crossover routing, maintaining substantial parallelism before and after the crossover, effectively cancels out cross talk interference by ensuring similar capacitance, resistance, and ground surface exposure, thereby reducing noise impact on victim trace lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional parallel routed signal conductors are used in high density areas, then circuit density and signal transmission speed are improved, but cross talk noise and signal interference increase
Solution Approach 1:
The patent applies inversion by swapping the positions of differential pair bus lines relative to aggressor bus lines at a crossover point. Before the crossover, the first differential pair is positioned at a first location; after the crossover, the first differential pair moves to a second location where the second differential pair previously was. This position inversion ensures that both differential pairs experience equivalent but opposite cross talk effects, which cancel each other out in differential signaling, thereby reducing net cross talk noise while maintaining high circuit density
2Area of stationary object
If signal conductors are placed in close proximity for high density routing, then area utilization is improved, but signal interference and cross talk increase
Solution Approach 1:
The patent converts the harmful cross talk effect into a beneficial cancellation mechanism. By strategically positioning the crossover point where differential pairs exchange locations, the cross talk noise induced on one pair becomes equal and opposite to the noise on the other pair. This transforms the previously harmful close-proximity coupling into a useful noise-cancellation mechanism, allowing high-density routing without sacrificing signal integrity
Data Source
AI summary
In one embodiment, a system comprises: a plurality of aggressor bus lines; and a plurality of differential pair bus lines that are located in relatively parallel close proximity to the plurality of aggressor bus lines, wherein at least two of the plurality of differential pair bus lines change location with respect to each other at a point that has a cancelling affect on cross talk from the plurality of aggressor bus lines, wherein the change includes cross over routing. The plurality of differential pair bus lines can convey differential clock signals. The routing of the plurality of differential pair bus lines is substantially parallel to one another before and after the change.