Cadence PCB Best Practices

Using Diff Pairs

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Using Differential Pairs in Allegro PCB Editor February 9, 2012 17 Product Version 16.5 A DRIVER pin is a pin with a pinuse of OUT, TRI, OCA or OCL A RECEIVER pin is a pin with a PINUSE of IN Example of pinuse on a net that will NOT consider the entire net a differential pair: Pin Type U1.12 TRI C1.1 OUT R1.1 OUT Example of pinuse on a net that WILL consider the entire net a differential pair: Pin Type U1.14 TRI C3.1 IN R3.1 IN Issue #2: How to Remove Electrical Differential Pair Objects from Constraint Manager I have deleted all differential pair properties from all the nets in my design, but some differential pair objects still show up in Constraint Manager. A right-click action on the differential pair in Constraint Manager displays a pop-up menu where I would usually delete the differential pair, but the Delete command is grayed out. How do I delete these differential pair objects? Solution: These differential pairs may have been electrically (or automatically) defined by a component's signal model. To remove these differential pairs, you must first determine the signal model that defines the differential pair and remove the differential pair definition from the signal model. To find the SIGNAL_MODEL 1. Right-click on the differential pair. The differential pair is highlighted in Allegro PCB Editor. 2. Choose Display > Element (Find Filter set to Comps only). 3. Select a pin of each component that is connected to the differential pair. 4. Look for the SIGNAL_MODEL property assigned to a component.

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