2 Replies Latest reply on Feb 9, 2012 9:14 AM by gary.felsman

    Formulas and Differntial Pairs


      I was trying to us a Formula to Match Differential pairs Signals in a group.


      I set a match Group Tolerance of 1200th


      The tried to reference all the Differential Paris to the Clock for that Group.


      So I entered the Formula to try and match each signal to the negative side of the Differential clock with a toleance of +850/-350th.




      When I go into Expedition and turn on the Tuning Meter. Expedition only sees the Match Group tolerance of 1200.


      This method works when I want to match single ended signals to a Differential Pair net.


      Any Suggestions on what to do?


      EE7.9.2 Update 5




      Gary Felsman

        • 1. Re: Formulas and Differential Pairs

          Happy New Year Gary:


          I don't know if you got any feedback privately on your issue but I did ask some of my "tuning meter and ces experts" -


          1.  It is true that the tuning meter uses the tolerance of the match group.


          2- But the values show up in the formula range.


          In the following example the actual length of the one end of the diff pair is 1318.165th.

          So the range of +850th and -350th is 968.165th and 2168.17th :


          The number in the middle of the tuning meter is the target longest length that is involved in the equation.


          Hopefully this helps you on your question.  If not, send some screenshots to explain your question it may help us to see your issue.

          • 2. Re: Formulas and Differential Pairs



            I got this to work I found a dangling net on the PCB causing the error.


            I did have another question which Mentor does not seem to have a solution for.


            I have three components


            1. CPU

            2. DIMM 0

            3. DIMM 1


            The route is from CPU to DIMM0 to DIMM1


            I know I can set an overall length for the entire length and set the routing order


            But How do I set a length from DIMM0 to DIMM1. *Example 0.385 inches."


            I am using Basic CES.


            When I look in CES the area where this would go is grayed out preventing any entires. (PADS can do this from a Webinar I attended. Mentor did not show the same capabilty. I asked but never got an answer)


            I went through a third party Layout hose to layout out my PCB and they could find an aswer either.


            Is this a known deficiency? Is there a plan to fix it?


            This is really important for DDR Down and multiple DIMM Configurations.


            I also tried this using Virtual pins and could enter segment length either.


            Thanks in Advance.