2 Replies Latest reply on Dec 10, 2013 8:04 AM by yxu1

    question on "virtual connect" in LVS


      Hi all,

      I want to use the "virtual connect" feature in LVS.

      Here's my simple test bench:

      In schematics view, I have 2 PMOSs, whose gates are physically connected together and the net name is "g1".

      In layout view, I also have 2 PMOSs, whose gates are connected to 2 separate poly's that are not physically connected but are given the same name "g1".

      Then in the "Connect" tab of LVS Options, I choose "Connect nets named: g1"

      I expect that, when I run LVS, all nets and instances should match.

      However, it didn't pass LVS and the LVS report is like this:


                                       INCORRECT NETS


      DISC#    LAYOUT NAME                                                    SOURCE NAME

         1        Net 1                                                                    g1




                       -----Devices on layout net 1 ---

                  X0/M0(-9.152, -2.605) MP(pfet)                                 MPM1  MP(pfet)

                      g: 1                                                                            g: g1

                      s: X0/3                                                                        s: net1

                      d: X0/4                                                                        d: net2

                      b: X0/5                                                                        b: net3


                       -----Devices on layout net 2 ---

                 X1/M0(-8.357,-2.641) MP(pfet)                                           g:g1

                      g: 2                                                                            g: g1

                      s: X1/3                                                                        s: net4

                      d: X1/4                                                                        d: net5

                      b: X1/5                                                                        b: net6



      Can you tell me what I did wrong? Thank you very much!

        • 1. Re: question on "virtual connect" in LVS

          Hi Yxu1,


          It looks like your text labels aren't working.


          Are there warnings of unattached text in the extraction report? It may be called lvs.rep.ext or some similar name.


          The log file/transcript will have a section "TEXT OBJECTS USED FOR CONNECTIVITY EXTRACTION" and there you should see the various text labels expected to be used for net names.


          As you try to solve the text issue, you can see if the results are improving if you notice "net names" instead of "net numbers" in the netlist extracted from layout.


          If the text labels aren't being attached properly you will see numbers in the layout netlist instead of names. For instance, one layout gate will be number "1" and the other will be number "2". Once the text labels are being properly attached to the nets then you might see "g1" for one gate and a number for the other (without virtual connection). And then finally, if virtual connection is also turned on as well as text labels being properly attached, then in the extracted netlist you should see "g1" for both gates.


          Best regards,


          • 2. Re: question on "virtual connect" in LVS

            After reading your reply, I realized I need to use "text label" on the net I want to "virtually connect".

            I thought I only need to name the poly in its Properties -> Connectivity -> Route Net Name.

            After placing text lables on the poly, the problem is solved.

            Thank you!