5 Replies Latest reply on Jun 29, 2010 10:13 PM by baenisch

    virtual join of schematic nets possible ?

    baenisch

      Hi all

       

      I have a question regarding the virtual joining of schematic nets. In my current project we're using two different

      gnd levels, gnd and bulkN. Both nets are joint a few hierarchies higher and sometimes also somewhere in between

      Therefore we can't get Calibre to keep both nets separeted in the lower levels, we always get shorts via substrate,

      which is technically ok of course.

       

      Is there a possibility, like joinNets in Assura, to virtually merge nets in the schematic netlist for LVS only, which

      would allow us to merge gnd and bulkN everywhere we need it ? The normal join option seems to work for layout

      networks only.  I also checked the manual, but I could find anything

       

      We could of course simply get rid of the seperation in our schematics, but this would be quite some work ...


      The other solution would be that the foundry would provide something like a markup layer so that Calibre could

      identify different substrate areas. Unfortunatly the foundry has not been a big support so far ...

       

      Some pointers would be appreciated

       

      Best Regards

       

      Andi

        • 1. Re: virtual join of schematic nets possible ?
          chris_balcom

          Hi Andi,

           

          I would expect the following statement to join the two ground nets in your schematic netlist. This statement could be manually added to the netlist. I'm not aware of a way to do this through the LVS rulefile.

           

          *.CONNECT gnd bulkN

           

          If that doesn't work, I would be interested to learn why. I guess I'm assuming that both of those names are also declared as global nets in your schematic netlist.

          • 2. Re: virtual join of schematic nets possible ?
            baenisch

            Hi Chris

             

            Hmm, I never thought of doing it the 'Spicey' way ... ok, I'll try and come back to you

             

            Thanks a lot

             

            Best Regards

             

            Andi

            • 3. Re: virtual join of schematic nets possible ?
              baenisch

              Hi Chris

               

              I just tried it out and the result looked quite promising at first. However two problems remain (if I trust the LVS )

               

              I get one "Incorrect Nets Error" as Calibre is complaining about a LAYOUT NAME Net BULKN vs SOURCE NAME ** missing net **

              and one "Incorrect Ports Error" LAYOUT NAME BULKN on net: BULKN vs. SOURCE NAME ** missing port **

               

              By removing the port bulkN in the Layout I could get the LVS to match, but I would still a LVS-only solution

               

              Best Regards

               

              Andi

              • 4. Re: virtual join of schematic nets possible ?
                chris_balcom

                Hi Andi,

                 

                That message indicates the BULKN port isn't really being shorted to the other ground in the layout. (if BULKN were connected to the other ground, BULKN wouldn't still exist as a separate net)

                 

                The *.CONNECT in the source netlist causes the two grounds to be joined together for the source, and that was done to mimic the shorting behavior in the layout, but now this seems like the layout isn't completely shorted after all.

                 

                If the BULKN port exists in the layout as a text object, You might consider remove the port by using an SVRF rulefile statement to "erase" the text label. If the text is placed at (12, 14) for instance, I think you should be able to delete the text using this rulefile statement:

                 

                TEXT 12 14

                 

                (by not specifying a text name or text layer, this statement functions to erase text at that coordinate)

                 

                Another possibility (that I don't recommend) would be to use LAYOUT RENAME TEXT to change that BULKN name to the other ground, then use VIRTUAL CONNECT NAME to join them all together but I think that's very risky because you could miss a "true open" with that method.

                • 5. Re: virtual join of schematic nets possible ?
                  baenisch

                  Hi Chris

                   

                  Sorry for coming back a bit late but I had a little bike crash and my important "mouse" hand limited

                  my work to more administrative topics . First of all, thanks a lot for the hints. Due to some other

                  problemes with our PDK we decided to get rid of BULKN and we moved everything to gnd. In our design

                  that should not be a problem, so this is the easiest way for us and we don't have to mess around in

                  the flow

                   

                  Best Regards

                   

                  Andi