Description
Overview: This check calculates the maximum trace length in which the differential pair is uncoupled. A differential pair trace segment is considered uncoupled if it’s projected distance from the other side of the differential pair.
Passing Criteria: There are two potential passing criteria for this check:
This check passes if the maximum percentage of uncoupled trace length is below a specified percentage of the total trace length.
If the above check does NOT pass, the check can still pass if the maximum uncoupled trace length is below a specified length tolerance
Reporting Units: Percentage OR Length (Microns)
Examples
Passing Message:
Uncoupled length of 1337.62µm within acceptable range (0µm to 10000µm)
Failing Message:
Uncoupled length of 15.32% outside acceptable range (0% to 10%)
Physics Justification
The distance between differential pairs is important because it affects how well they work together and resist interference. A few reasons this is important:
Electromagnetic Coupling
Differential pairs create small electromagnetic fields as signals travel. If the traces are too far apart, they won’t couple well, reducing their ability to cancel out external noise. If they’re too close, they might interfere with each other or other signals.
Crosstalk
If differential pairs are too close to other traces, their signals can interfere with neighboring traces (or vice versa), causing crosstalk, which is unwanted noise from other signals.
Impedance Control
The spacing affects the differential impedance, which is the resistance the signals encounter. Maintaining a specific distance ensures the impedance stays consistent, helping the signal stay clear and fast.
Helpful Definitions
Crosstalk:
Crosstalk is unwanted interference caused by signals in one trace inducing noise into a nearby trace. It happens because the electromagnetic fields from one trace can "leak" into another, disrupting the signal.
Differential Impedance:
Differential impedance is the combined resistance a differential pair encounters as signals travel together. It's determined by the trace width, spacing between the traces, and the surrounding materials. Proper impedance ensures the signal integrity without reflections or losses.