eCADSTAR - Routing - Differential Pair Configuration

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Video Transcript


In this eCADSTAR demonstration we are going to look at basic configurations and routing of differential pairs in the PCB Editor.

First of all we open our constraint browser, then I click on the create multiple differential pairs icon. This scans both Enets and net lists for matching names with a differentiating suffix which you can also customize here.

You can use nets or Enets as your target object for example if you have passive components in between your differential pairs you will use the nets as the target object instead.

The constraint browser automatically assigns a name using your net or Enet names.

I now need to assign a rule stack to them. This is one I have configured earlier so I am going to assign this rule stack and we will have a look and see how I have set this up.

In my differential pair rule-stack, you can see I have defined track widths and spacings. I now select calculate differential impedance, then using my track widths, spacings and PCB material stack up the embedded field solver returns the expect impedance and delay values. The calculation feature to the left of this incorporates the use of a target impedance for more complex designs.

Now with our rules defined let’s see how this affects our routing environment. When selecting one of the nets it automatically picks up the second one and routes them both at the same time, whilst adhering to the rule stacks we defined earlier.

On the approach to the final connection, you can see a directional arrow. This is indicating that my nets are crossed and it would be better to approach from the opposing side.

Let’s repeat that again with another differential pair.

And that’s how you setup and route basic differential pairs with the useful features in eCADSTAR.


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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