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 Level shifter cell alignment in rows 

Last post Thu, Feb 28 2013 3:23 AM by Franchie. 2 replies.
Started by Franchie 27 Jan 2013 02:38 AM. Topic has 2 replies and 1086 views
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  • Sun, Jan 27 2013 2:38 AM

    • Franchie
    • Not Ranked
    • Joined on Sun, Jan 27 2013
    • Posts 2
    • Points 25
    Level shifter cell alignment in rows Reply

    Hello,

     

    I am working on a design that uses a number of level shifters, whose height is unfortunately not a multiple of the standard cell height (level shifter height is 3.9µm whereas the standard cell height is 2.6µm).

    In order to accomodate this, as per the recommendations in the NIMH section of the Floorplan design user manual, I have set up seperate power domains for all the different types of level shifters, containing only instances containing just level shifter cells, and create the rows within these power domains via the createRow command, specifying the new appropriate core SITE to use:

    createRow -site CORE_LS -noFlip -noAbut -spacing 1.3 -powerDomain PD_LS1

    This creates the correct rows, but unfortunately during the placeDesign (and refinePlace) steps, the level shifter cells are not placed within these rows, and in such a way that the followpins that are created do not line up properly with the power rail connections within the cells.

    While it is possible to force correct alignment of these cells through the use of the snapFPlan and some scripting, violations are generated, and some domains have incomplete followpins.

    Therefore could anyone give me some guidance as to how to align these level shifters properly within the rows of their respective power domains to avoid such problems?

     

    Thank you for your time and trouble,
    Franchie. 

     

    • Post Points: 20
  • Wed, Feb 27 2013 8:05 AM

    • Kari
    • Top 10 Contributor
    • Joined on Tue, Jul 15 2008
    • Cary, NC
    • Posts 693
    • Points 14,295
    Re: Level shifter cell alignment in rows Reply
    i'm not an expert in this, but can you confirm that those level shifters are assigned to the right domain? if they are, I would think they should get placed on the proper rows.
    • Post Points: 20
  • Thu, Feb 28 2013 3:23 AM

    • Franchie
    • Not Ranked
    • Joined on Sun, Jan 27 2013
    • Posts 2
    • Points 25
    Re: Level shifter cell alignment in rows Reply

    Hello, and thanks for your help!

    Because the level shifters are not multiples of a standard cell height, according to the Cadence documentation they must be placed in their own power domains. This was done, I believe, correctly, but still did not align them with the rows.

    The tape-out has passed now, so I gave up trying to find a solution to this and instead concentrated on getting the cells in the right place through less elegant methods. I was able to get limited success by using the adjustPowerDomainToAlignRows command, which resized the various power domains in order to align their rows.

    This worked for all but one level-shifter power domain, where the limited number of cells allowed me to place them manually.

    Once aligned, I set them all to fixed, so that they were not moved during later stages of the flow.

    Lastly, the followpins were in each case not created correctly. In order to solve this I wrote a tcl script that identifies the level shifter rows and creates the wire via the addWire command.
    In this way I was able to create all the wires with minimal effort.

    So unfortunately I was never able to identify the cause of the problem, but was able to get around it with the methods outlined above.

     

    Thank you for your help in any case, it is really greatly appreciated! 

    • Post Points: 5
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Started by Franchie at 27 Jan 2013 02:38 AM. Topic has 2 replies.