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Difference function in pcell designer geo query

AKMush

Hi,

I wanted to do a simple 'shape A - shape B' operation in PCD's geo query (return shape A with its overlap with shape B removed). I thought the difference function, which has a description:

where an input like

would accomplish this. However, no matter what I do it only seems to return the first shape in it's input list with no modification. Is this more of a list operation and not an explicit shape one?

Additionally, I have found using the landnot(A B) achieves what I wanted, which means this is doing A ∩ not(B), this actually disagrees with its icon which implies (A U B) ∩ not(A ∩ B):

Can I get some clarification on landnot() and difference()? There doesn't seem to be documentation on them (or at least I couldn't find any). Is there comprehensive documentation on PCD?

Thanks!

Parents
  • +1

    As there is a dedicated forum for PCell Designer, I moved this post into that forum.

    You've misunderstood the difference between the "layer" and/or/andnot operators and the "or", "and" and "difference" operators.

    The or/and/difference work by dealing with lists of shapes. It does not consider the portions of shapes that overlap, for example. "or" produces the combined set of shapes - in other words all inputs in a single flat list (so shapes in both inputs only appear once in the output). The "and" produces only those shapes that are in both inputs. The "difference" returns the shapes in the first input which are not in the second input.

    The lor/land/landnot are geometric boolean operators. The first produces geometries that merge the areas of the two inputs. The land only gives you the overlapping regions. The landnot gives you the regions of the first shapes which are not covered by the second shapes. You're reading an awful lot into a tiny icon - given that it can't unambiguously show the two inputs and the output clearly on such a tiny icon, I really can't see how you've come to your conclusion. I see that icon as having the first shape being an "L" shape (rotated by 180 degrees) and the second shape being a square in the top right corner. The red regions are the output of the operation. 

    Maybe this picture (which comes from our training class on PCell Designer) makes it clearer:

    The orange shape is the first input, and the green rectangle is the second input. The white highlight shows you the result of the operation.

    To answer your question on documentation; we have a preliminary (incomplete) reference manual which can be shared through customer support, but we now have somebody in the tech pubs team who is working on completing//editing the reference guide and then creating a user guide after that. These will then end up in the documentation on support.cadence.com - I am hoping that we'll have the reference manual finally ready by the end of the year. In the meantime, please contact customer support and mention this post (give a link to it) and ask that the AE contacts me and then I can share with you the material we have so far Apologies that the documentation has rather lagged behind the development of the tool, but we're finally addressing that.

    Regards,

    Andrew

Reply
  • +1

    As there is a dedicated forum for PCell Designer, I moved this post into that forum.

    You've misunderstood the difference between the "layer" and/or/andnot operators and the "or", "and" and "difference" operators.

    The or/and/difference work by dealing with lists of shapes. It does not consider the portions of shapes that overlap, for example. "or" produces the combined set of shapes - in other words all inputs in a single flat list (so shapes in both inputs only appear once in the output). The "and" produces only those shapes that are in both inputs. The "difference" returns the shapes in the first input which are not in the second input.

    The lor/land/landnot are geometric boolean operators. The first produces geometries that merge the areas of the two inputs. The land only gives you the overlapping regions. The landnot gives you the regions of the first shapes which are not covered by the second shapes. You're reading an awful lot into a tiny icon - given that it can't unambiguously show the two inputs and the output clearly on such a tiny icon, I really can't see how you've come to your conclusion. I see that icon as having the first shape being an "L" shape (rotated by 180 degrees) and the second shape being a square in the top right corner. The red regions are the output of the operation. 

    Maybe this picture (which comes from our training class on PCell Designer) makes it clearer:

    The orange shape is the first input, and the green rectangle is the second input. The white highlight shows you the result of the operation.

    To answer your question on documentation; we have a preliminary (incomplete) reference manual which can be shared through customer support, but we now have somebody in the tech pubs team who is working on completing//editing the reference guide and then creating a user guide after that. These will then end up in the documentation on support.cadence.com - I am hoping that we'll have the reference manual finally ready by the end of the year. In the meantime, please contact customer support and mention this post (give a link to it) and ask that the AE contacts me and then I can share with you the material we have so far Apologies that the documentation has rather lagged behind the development of the tool, but we're finally addressing that.

    Regards,

    Andrew

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