a question from a Cadence beginner:
The problem is:
- I have a simple NAND schematic. This schematic uses pcell mosfets for circuit simulation.
- Now I want to design my own layout for this schematic using Virtuoso XL layout editor
In my case I want to design the mosfets by hand, not using the prebuild / automatically generated pcell layouts from the library.
When I'm designing my mosfet by hand in VXL, the program highlights the DIFF/Poly crossing (channel) to indicate an error. I'm not really sure why, but it seems as if the program is not able to find a corresponding channel in the schematic and the highlighted error indicates a mismatch between schematic and layout.
A DRC doesn't report any errors and the mosfet's width & length is exactly matching the values of the corresponding transistor in the schematic - so the "selfmade" layout of the mosfet is definitly ok.
Another way I tried is placing a mosfet pcell from the library and flattening it's hierarchy to optimize it's structure (for example the adjustment of the location and the number of source / drain contacts). But as soon as I flatten the hierarchy of the pcell, VXL looses the "connection" between pcell in schematic and it's corresponding (now flattened) layout. Again the DIFF/Poly crossing gets highlighted.
The main problem is that a LVS run now results in missing instances and unknown nets in layout although they are there. The LVS doesn't seem to recognize the correspondance between "selfmade" layout parts and instances in the schematic.
The strange thing I recognized is, that prebuild digital standard cells pass the LVS without any errors - although they are also made up of a schematic using prebuild pcells and a selfmade layout without the use of those pcells...
I hope the problem description is understandable...So finally my question is:
Is it possible to tell VXL something like: "Those parts in the layout window correspond to instance XYZ in the schematic"? This would at least prevent the LVS from reporting missing instances in layout.
Thanks for any answer / help on this subject! Originally posted in cdnusers.org by designer