3 Replies Latest reply on Jul 2, 2013 4:06 PM by Vern_Wnek

    How to get differential pairs to match in length

    sjy89

      Hello,

       

      In Expedition PCB how do you get all the differential pairs you want to match identically in length (or close to it)?

       

      Thanks,

      Steve

        • 1. Re: How to get differential pairs to match in length
          Vern_Wnek

          Steve,

           

          By design, Diff Pairs in Expedition are matched as closely as possible when routed - often to sub-mil measurements. If you are trying to create a Matched Group of Diff Pairs, then here are a few resources that should point you in the right direction.

           

          Video:

          http://supportnet.mentor.com/portal?do=reference.tutorial&id=MG576719&lang=en&prod=C107-S123-G192-P10287

           

          The CES On Board Series site:

          http://communities.mentor.com/community/pcb/expedition/onboard_series?cmpid=7265

           

          The CES Quick Design Guide which can be located at the link above on the Overview page.

           

          These are all great resouces for the beginner, just starting to learn CES, as well as Advanced users who need a little refresher.

           

          Good Luck,

          Vern

          1 of 1 people found this helpful
          • 2. Re: How to get differential pairs to match in length
            sjy89

            Vern,

             

            Thank you so much for your feedback!

            It is much appreciated and your help definitely brought me much closer to the solution but, I also wanted to make it clear that I want all of my differential pairs that are on my design to be exactly or very close to equivalent lengths.

             

            I'm very sure the material you recommended to me will solve the problem but, if you know how to do this that'll be great!

             

            Again thank you very much,

            Steve

            • 3. Re: How to get differential pairs to match in length
              Vern_Wnek

              Steve,

               

              I am going to assume that you already have your Diff Pairs created in CES. If not, you will need to create these first.

               

              Once they are created, follow these steps: (Refer to Screen shot)

               

              1. Create a New Constraint Class, call it DiffPairs or something of your liking.

              2. Select the Diff Pairs you created using CES and RMB > Assign to Constraint Class, choose the class from step 1.

              3. Assign a Match Tolerance at the Top level of the Constraint Class. This is the amount in which the Diff Pairs will be matched to. .250 in my example

              4. Route the Diff Pairs in your design. You must route all of the Diff Pairs in the Matched Group before you can Tune them.

              5. Once all are routed, select the nets and use the Tune Action Key (F4) to tune the nets per the Tune settings in your Editor Controls.

               

              Note: Even though my tolerance was .250, they are much more tightly matched than the Tolerance allowed.

               

              I hope this gets you there...

               

              MatchedDiffPairs.png

               

              Good Luck,

              Vern