> For the complete documentation index, see [llms.txt](https://docs.quilter.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.quilter.ai/physics-rule-checks-prcs/uncoupled-spacing.md). # Uncoupled Spacing ### Description **Uncoupled Spacing** calculates the maximum trace length in which the differential pair is uncoupled. The nominal spacing is determined based on desired differential impedance and the specific stackup. A differential pair trace segment is considered “uncoupled” if it’s projected distance from the other trace in the other net is outside of a tolerance of 10% when compared to the nominal spacing. **Passing Criteria:** \ This check passes if the trace length of uncoupled spacing between the two trace paths in the nets of interest is below a specified length tolerance **Reporting Units:** \ CENTIMETERS (cm) ### **Examples** **Passing Message:** {% hint style="success" %} Uncoupled spacing of 0.06cm within acceptable range (0cm to 1cm) {% endhint %} **Failing Message:** {% hint style="danger" %} Uncoupled spacing of 6.57cm outside acceptable range (0cm to 1cm) {% endhint %} ### Physics Justification The distance between differential pairs is important because it affects how well they work together and resist interference. A few reasons why this is important include: * **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. Conversely, if they’re too close, they might interfere with each other or with 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 remains consistent, helping the signal to 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. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.quilter.ai/physics-rule-checks-prcs/uncoupled-spacing.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.