eCADSTAR - Routing - Differential Pair Configuration

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Video Transcript


In this video we are going to look at the basic configuration of differential pairs in eCADSTAR. So, outside of any timing or length matching requirements. And it couldn’t be easier to set this up. First of all, we use our Constraint browser which can be invoked from either the Schematic or PCB.


Next I use the ‘Create multiple Differential Pairs’ feature and you can see it’s scanned the entire netlist and identified nets with a matching name but importantly they have a differentiating suffix. The SW automatically assigns the differential pairs a name but I can override this if I want. I now need to tell those differential pairs which set of rules I would like them to use for their track and gap spacings. We refer to these in eCADSTAR as a Differential Pair Rule Stacks.


These can be saved in your library.  They can be exported and imported and quickly shared amongst the rest of the design team. I already have one configured so I’ll point to it in here and then we’ll go take a look at how we can set those up in the Rule editor.

In my Differential Pair Rule Stack you can see I now have some standard geometry defined. I now click on Calculate impedance and the SW runs the embedded field solver which looks at our PCB material stack up and these track and gap configurations here and it will return the expected impedance.

We can run it the other way as well. Input target impedance and it will return track and gap spacings for us.


Now with the pairs defined and the rules checked let’s see how the routing environment handles this information. When either of the nets are selected in the pcb it will simultaneously route the second one for us, whilst adhering to the track and gap spacings we configured in the Rule stack. Here you can see the geometry difference when I transition to layer 4.

As I approach this filter, I need to return to the top layer to make connections but the router knows this already and it is automatically adding vias for me. I’m just driving my cursor towards the connection point.

When I approach the final connection there is a directional arrow telling me that the connections are crossed and it would be better to approach from the opposite direction. Let’s see this again on a second pair.

So it’s really easy to configure standard differential pairs in eCADSTAR.  A good consistent naming convention for your nets will certainly help automate the process.

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