Using Differential Pairs in Allegro PCB Editor
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Tandem Routing
You might need to route the two nets of differential pair on adjacent layers. This does
not happen automatically in Allegro PCB Editor or Router. However, it is possible to
tandem route differential pairs manually.
When routing the differential pair on different layers, the rules you set in Constraint
Manager will not have any effect.
To route a differential pair on tandem layers, perform the following steps. This
procedure assumes that routing will be done on the top layer and layer 2.
1. Pick the first net, for example, Net1 of the differential pair for routing.
2. Right-click and select Single Trace Mode from the pop-up menu.
3. Route the single trace just a small segment on the top layer, click to add a
corner, and right-click and select Done.
4. Select the second net of the differential pair for example, Net2 for example, at the
route layer with layer 2.
5. Route Net2 to where you ended Net1 of the differential pair and add a corner to
coincide with the net on the top layer.
6. Right-click and select Done.
You will now have the segment on the top layer for Net1 and the segment for Net2 on
layer 2 exactly on top of each other.
7. Select Net1 or Net2, right-click and uncheck Single Trace Mode.
The differential pair will now route together. To complete the routing, use the same
method that was used to start the tandem routing.
