2 Replies Latest reply on Aug 12, 2013 4:33 PM by Aravindhan

    DRC and LVS error for simple inverter using calibre

    Aravindhan

      Hi,

       

      I was starting out actual layout of  my circuit but started to face some issues with drc/lvs. So i had decided to do a simple inverter to make sure my calibre is using the right rule files for drc and lvs. Please find attached my inverter's schematic (sizing shown in the picture) and layout.I am using IBM 130nm PDK.

       

      I have observed the following:

       

      1. If I use the NW contact available during the instantitation of PMOS which attaches/abuts the NW contact along with the PMOS, my DRC is clean. Whereas if I dont use that option, its throwing me DRC errors[document attached for that] related to chipedge. Why is it so ?

       

      2. I have also attached the LVS errors (document attached) which are same in both the cases - whether I use the automatic option of NW contact or drawn maunally. I am not able to figure out why this error comes even though the connections, source of pft/nfet and sizing everything is same in schematic and layout. The error says my instances are mismatched. I am using fingers in both schematic and layout.

       

      3. A. I have one generic question- If we have many nfets in the schematic, should we use one subc symbol each for each nfet in schematics to pass the LVS or can we use just use one subc symbol and connect all sources and bulk to it.

          B. From the perspective of lvs, is it advisable to use the automatic option of subc contact available in the PDK for layout or manually draw it ?

       

      Thanks.

       

      Best,

      Aravindhan

        • 1. Re: DRC and LVS error for simple inverter using calibre
          chris_balcom

          Hi Aravindhan,

           

          The problem appears to be in the connections of the devices on the schematics, or maybe a power naming issue. You may find more clues by looking at the netlist for the source to see how the power and ground are connected to the devices in the source. Calibre needs to find power and ground for the devices in order to make the inverter and that seems to be happening ok in the layout but not the source. Another thing you could experiment with is to temporarily use LVS INJECT LOGIC NO (along with LVS RECOGNIZE GATES NONE) so that the devices in this case won't be transformed to an inverter in the layout and then you will see the errors reported in a different way. Sometimes having the errors reported in a different way makes them easier to debug.

           

          Best regards,

          -chris

          • 2. Re: DRC and LVS error for simple inverter using calibre
            Aravindhan

            Hi Chris,

             

            Thanks for your reply. As you had pointed out rightly, it was a mistake in the schematic. The error I made was in the subc connection. I had fixed the same somtime back but forgot to update the same in the forum. And now I am not having any issues on that.

             

            Thanks for your attention in this matter.

             

            Best,

            Aravindhan