To set the differential pair spacings as shown above, do the following within the Constraint Manager:
1. Go to Spacing > Net > All Layers. Notice the Net Class (NCls) named DIFFPAIRS(25).
2. We'll make a class-to-class rule that says any differential pair to another differential pair will have a certain spacing
(intra-pair), and any differential pair to any other class of nets will have other kinds of spacing (inter-pair)
3. Go to the Net Class-Class > All Layers worksheet.
4. A new window, Create ClassClasses, appears. Under the NetClasses sections on the left and the right, select DIFFPAIRS
for each, then click Apply. The list will populate with that class-to-class spacing for intra-pair spacing.
5. For the inter-pair spacing (diff pairs to all other net classes), select DIFFPAIRS in the left column and MISC in the right
column.
40 www.cadence.com
OrCAD X High-Speed Digital Design Guide
