1 2 First Previous 15 Replies Latest reply on Dec 6, 2010 7:14 AM by radike_d

    Calibre LVS PEX Warnings and Erros

    radike_d

      Hi,
      I am new to IC design using Cadance. I finished my layout and now trying to run LVS and PEX using Cadance. To run Calibre LVS, I first exported the schematic netlist from Export -> CDL_OUT option.

      Then I included this file as my source netlist in the LVS setup.

       

      When I run LVS I am getting the following Warnings.

       

      WARNING: There is no data for layout net name __USER_DEFINED_LVS_POWER_NAME__

       


      WARNING: There is no data for layout net name __USER_DEFINED_LVS_GROUND_NAME__

       

      WARNING: Invalid PATHCHK request "GROUND && ! POWER" : no POWER nets present, operation aborted

       

      WARNING: Invalid PATHCHK request "POWER && ! GROUND" : no POWER nets present, operation aborted

       

      WARNING: Invalid PATHCHK request "! POWER && GROUND" : no POWER nets present, operation aborted

       

      Is it possible to know how to clear these warnings?

      Also, now when I run the PEX simulation I get the following errors

       

      ERROR: There is no usable returns path nets in the PDB for inductance extraction.

       

      ERROR: Net information could not be built.

       

      ERROR: The inputs for inductance engine were not properly built.

       

      I also get the warnings same as warnings in LVS. The above errors are related to parasitic Inductor extraction. I am not sue whether it because of the warning in LVS. 

       

      Can somebody help me regarding this?

       

      Thanks a lot!!!

        • 1. Re: Calibre LVS PEX Warnings and Erros
          samantha_lizak

          Hi-

           

          I can't help much with the LVS issue -- I'm hoping Chris Balcolm or someone knowledgable about Cadence/Calibre integration steps in -- but I do know that you can't run PEX until you have a clean LVS.  Parasitic extraction uses the connectivity information that LVS generates.

           

          -Sam.

           

           

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          • 2. Re: Calibre LVS PEX Warnings and Erros
            radike_d

            Hi,

             

            Thank you for the reply. I found that when I ignore the ERC check, the warnings for power and ground lines in LVS and PEX does not come. Also the error in PEX does not appear when don't select parasitic inductance extraction. Do you know any reason for this?

             

            Thanks a lot!!!

            • 3. Re: Calibre LVS PEX Warnings and Erros
              chris_balcom

              > WARNING: There is no data for layout net name __USER_DEFINED_LVS_GROUND_NAME__

               

              For the warning above, there may be a place in the rulefile where you would type the ground names you actually use. The name or variable called "__USER_DEFINED_LVS_GROUND_NAME__'

              may be just a placeholder waiting for you to change to the ground name used in your design.

               

              > WARNING: Invalid PATHCHK request "GROUND && ! POWER" : no POWER nets present, operation aborted

               

              For this warning about PATHCHK, it seems to be because the real ground names aren't being used. Usually there would be something like VSS or GND instead of "USER_DEFINED_LVS_GROUND_NAME" (and the same idea applies for the power name).

               

              If those warnings went away when you turned off the ERC checking, it may be that ERC was the only operation requiring power and ground names to be clean and working (PATHCHK is a typical ERC type of operation)

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              • 4. Re: Calibre LVS PEX Warnings and Erros
                samantha_lizak

                Hi Radike-

                 

                The PEX warnings you mentioned were all inductance related. I'm not surprised that when you are not doing parasitic inductance they don't occur. :-)

                 

                In light of Chris' reply about the LVS errors, the specific inductance issue probably had the same root cause. The first PEX error mentioned "returnpath". That means your rule file is trying to run some form of loop inductance calculation. The loop is formed between a signal net and a return path, typically power or ground. (There is an SVRF command that restricts it to one or the other. I think you may also be able to specify another signal net as the return path.)  As Calibre LVS could not identify the ground net (the LVS error), there was an invalid return path, and xL couldn't complete either.

                 

                There's an explanation in the xL User's Manual of the different types of inductance calculations you can do, if you keep getting that returnpath error. I seem to recall at least one of them used "piecewise inductance" or "piecewise impedance", and worked by inferring a return path instead of calculating it. It may have been certain Calibre versions only; I've been away from PEX for a while and it has undergone many changes.

                 

                Best regards-

                 

                Sam.

                 

                 

                 

                 

                • 5. Re: Calibre LVS PEX Warnings and Erros
                  radike_d

                  Hi Chris,

                   

                  I actually changed __USER_DEFINED_LVS_GROUND_NAME__ to my actually ground name (gnd). Then the same warning repeats

                  WARINING: There is no data for layout net name gnd

                   

                  I ran PEX and it shows the extracted parasitics. Next  in analog environment->environment option-> I changed "spectre cmos_sch cmos.sch schematic veriloga ahdl"  to  "calibre spectre cmos_sch cmos.sch schematic veriloga ahdl" and ran the simulation.

                   

                  However, results are the same as the schematic. Is it possible to know my approach is correct and whether this is due to the warnings?

                   

                  Thanks a lot!!!

                  • 6. Re: Calibre LVS PEX Warnings and Erros
                    radike_d

                    Hi Samantha,

                     

                    Thanks for the reply. Regarding the different types of inductance calculations, are you referring to the self and mutual inductance which can be selected from the PEX setup?

                     

                    Thanks and Regards,

                     

                    Radike

                    • 7. Re: Calibre LVS PEX Warnings and Erros
                      chris_balcom

                      The earlier warning was describing that "USER_DEFINED_LVS_GROUND_NAME" didn't exist, and that should be expected because it's unlikely to actually have a text in your layout by that name.

                       

                      This new warning about "gnd" not existing is still describing that there is no texted net by the new name either.

                       

                      For texted names to be found, there would need to be text labels in the layout database, and also TEXT LAYER statements in the rulefile that use the same layer number as the text in the layout, and frequently ATTACH statements are needed as well to associate the text layers with other connectivity layers when they aren't on the same layer as each other.

                      • 8. Re: Calibre LVS PEX Warnings and Erros
                        radike_d

                        Hi Chris,

                         

                        In my layout I labeled my nets with the corresponding metal label. Then I created pins from the labels and assigned the corresponding metal layer for the pins. However, I still get the warnings.

                        • 9. Re: Calibre LVS PEX Warnings and Erros
                          filipedos

                          For inductance extraction, you need to specify a return path for your self. In calibre interactive menu go to "PEX options -> LVS options-> Ground nets" and specify a ground net (for instance "path")

                           

                          In your layout put a metal rectangle alone with the label "path".

                           

                          Normally your extraction with parasitic L should run.

                           

                          Hope this help you

                          • 10. Re: Calibre LVS PEX Warnings and Erros
                            chris_balcom

                            Hi Radike,

                             

                            If Calibre sees the text there should be mention of them in the transcript. For instance, if the text is "gnd" then you might grep or search the log file for "gnd" and see what is there. If there are warnings about shorts or opens, then the "gnd" could be discarded for those reasons. If there is no mention of the "gnd" text at all (such as with a layer number and coordinate showing where the text is) then you may not have the TEXT LAYER statements matching properly with the "gnd" text in the layout.

                            • 11. Re: Calibre LVS PEX Warnings and Erros
                              radike_d

                              Hi,

                               

                              Thanks for the reply. I tried same way you mentioned. I am still getting the same warnings.

                              • 12. Re: Calibre LVS PEX Warnings and Erros
                                radike_d

                                Hi,

                                 

                                I checked in the log file. For each labels there are coordinates specified in the text.

                                Is it possible to know whether, with these warnings whether I can get the correct extraction results? Because, I was able to simulate PEX (Only R, C extraction) and it shows the extracted results. The circuit is s simple one transistors biased with V_G (Using 1 kohm res) and V_D(Using an Inductor). Also I have two DC blocking capacitor at the input and the output of the circuit. However, my results are totally wrong. According to the schematic I get 16 dB of gain (S21) but post layout simulation gives -50 dB.

                                 

                                Thanks a lot!!

                                • 13. Re: Calibre LVS PEX Warnings and Erros
                                  chris_balcom

                                  Hi Radike,

                                   

                                  Which warnings are you still seeing? The "no data for gnd" warning or the "invalid pathchk request" warning?

                                   

                                  If the coordinates for the text show in the transcript that is a good indication that Calibre can see the text. If there is a warning such as "no data for net name gnd" then that would mean the text was found but not actually used. If it wasn't used then that is usually because it was floating, or involved with a short or open. Any of those problems should have caused a warning that lists the text name again.

                                  • 14. Re: Calibre LVS PEX Warnings and Erros
                                    samantha_lizak

                                    Hi Radike-

                                     

                                    I might be being overly jumpy, but want to be sure you are not using the parasitic extraction results in place of your device models.  Parasitics are the UNintentional electrical effects; that is why historically it has been focused on interconnect. Device characteristics are generally supplied as part of the library.

                                     

                                    Also, if you are trying to measure parasitics within a device (as opposed to on the interconnect), you'll be better off with Calibre xACT than Calibre xRC. xACT uses field solvers, whereas xRC uses model-based calculations. Fortunately, the set up and rules are almost entirely the same. Unfortunately, xACT is after my time and I'd need to hand you off to someone else if you have questions on it.

                                     

                                    Best regards-

                                     

                                    Sam.

                                     

                                     

                                     

                                     

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