8 Replies Latest reply on May 3, 2012 4:12 AM by Govind_kulkarni

    Overlapping cells in GDS


      Hi, is there any utility in place in calibre or calibreDRV to report the overlapping cells in a GDS?

        • 1. Re: Overlapping cells in GDS

          I'm not sure. But in Calibre itself you can check for overlapping shapes. For instance, if you want to check for overlapping layer WELL


          WELL_OVERLAP = WELL AND > 1


          THis only works if "WELL" is an original layer

          • 2. Re: Overlapping cells in GDS

            I wonder if DesignRev and Calibre could be combined to accomplish this. A short DesignRev script to create simple polygons based on the individual extents of each cell placement, then feed that layer into the single layer AND operation that Hartmut mentioned for Calibre.

            • 3. Re: Overlapping cells in GDS

              I remember I had this kind of question already earlier with a customer. It is a very difficult problem. If you can assume all cells to be rectangular, than you can use then command "$L bbox" in designrev to generate a layer with cell outlines, which then can be cheked for overlap with the single layer AND in Calibre.


              However, if cells are rectilinear, or there is no automatic way to generate a cell outline layer. This has to be done manually.


              Even in the simple case of rectangular cells, there is the problem that the single layer and command is not cell specific. So if you want to check overlap for a cell "A", but the cell contains a subhierarchy with a cell "B" for instance, then all cell B outlines will be flagged.


              Probably the only useful solution could look like this:


              1.) Create an outline layer for all cells.

                   a) If cells are rectangular, it could be done with "$L bbox" in designrev.

                   b) for all other cases, this has to be done manually


              If you generate the outline layer only for the relevant cells, you can skip step 2 (Even then you should worry about icells)


              2.) Specify a list of cells, for which ovlerlap has to be checked. Use designrev to remove the cell outline shapes in all other cells and from all cells in the subhierarchy of the cells to be checked. This can become tricky in case you have "icells" (cells which are both in the subhierarchy of the cells to be checked, but also instanciated elsewhere)



              3.) Use single layer AND in Calibre to check overlap of the cell outline layer.

              • 4. Re: Overlapping cells in GDS

                We have the PnR blocks having std cells instantiated. We want to check if there are any overlapping cells after receiving the PnR block. Sometimes the legalization of cell is not proper due to placer tool or by some post processing script and it results in overlapping cells.


                So, this is what I tried based on the suggestions in this thread.

                All the std cells have this PrBoundary layer as their boundary. If the cell placement is correct, then PrBoundary of respective cells abut each other. If one PrBoundary is extecnding inside other PrBoundary, that would mean its a cell overlap.

                I tried the AND > 1 operation for the PrBoundary layer and ran the flat DRC. It reports 1 violation and highlights a 76-vertex polygon of PrBoundary (all merged).


                -----                   LAYER READ SUMMARY (GEOMETRIES)                    -----
                SIMPLE LAYER     GEOMETRIES                  ORIGINAL LAYER           GEOMETRIES

                     1080          602604                    PRBOUNDARY                 602604

                • 5. Re: Overlapping cells in GDS

                  The 76-vertex output shape should appear only in the locations of overlap. Are there overlapping cells limited to one complex interconnected group of cells in the design?

                  • 6. Re: Overlapping cells in GDS

                    No, this block did not have any overlaps. I intentionally created one cell overlap and was hoping to catch it with AND PRBOUNDARY.

                    Calibre merges the shapes on this layer before doing any boolean operation. I tried the "LAYOUT MERGE ON INPUT NO" as well but that did not work out.


                    Then, I also flattened two cells so that the two overlapping polygons are at the top cell. It still does not catch the overlap.

                    • 7. Re: Overlapping cells in GDS

                      Any inputs for this problem?

                      • 8. Re: Overlapping cells in GDS


                        Try using CUT command instead of AND, and you have to use hirerachy run to avoid the merging of layers before the logical operation.


                        Govind Kulkarni