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Problem with addWellTap command

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Hi,

The standard cell I am using does not have substrate and n-well tap, so I have to placed well tape cell at regular interval in the core.

My perference is to use place them in checkerboard fashion. But I am hit with what I believe is a limitation in the command addWellTap. It is not easy to explain, so please be patience.

Let assume the max distance between the well tape is 40um (to simplify, we ignore the width of the well tap and the height of the cell row). So the command to add well tap should be:

addWellTap -cell wellTap -cellInterval 160 -checkBoard

The cell interal is 160um because a well tap can cover 40um on both side. Also, in between the two cell taps on the same row, there are two well tapes on the upper and lower row which are exactly in the middle. Hence the spacing is 160um. The following drawing explain this:

(Note: X is the tie cell)

           X             X 
XXX
           X             X  


The problem occur when the upper or lower row is not available to place the well tap cell (e.g. due to macro or placement blockage). In this case, the tool shold place the well tie cell 160/4 or a max of 40um away from the edge of the row. The tool now place it 160/2 or 80um away. This is incorrect from my application of the command:


.............             X
... Macro ...     X
.............             X
.............X
.............             X
      X           X
X                  X                      X


The distance marked "!" above is less than 160/2, but larger than 160/4. So an DRC will occur here.

Is there a workaround or hidden switch to get this command to work? Thanks.

Regards,
Eng Han







Originally posted in cdnusers.org by EngHan
Parents

  • Hi Mohan,

    It is not easy to shift the macro as the design has more than 100 macro of different sizes.

    The option "-fixedGap" does not take an argument. So we can only either say "-maxGap 160" or "-cellInterval 160". The issue is that the tool will always take 160/2 as the maximum allowable distance. This is not true for checkerboard style.

    More info on where the issue can happened:
    1. Between the left side of the core to the left side of a macro (a small area for buffering and JTAG cell)
    2. Between the right side of a macro to the right side of the core (a small area for buffering and JTAG cell)
    3. on the left and right side of the macro
    4. A single row betweent two macros (at the right side of these rows)

    Regards,
    Eng Han


    Originally posted in cdnusers.org by EngHan
Reply

  • Hi Mohan,

    It is not easy to shift the macro as the design has more than 100 macro of different sizes.

    The option "-fixedGap" does not take an argument. So we can only either say "-maxGap 160" or "-cellInterval 160". The issue is that the tool will always take 160/2 as the maximum allowable distance. This is not true for checkerboard style.

    More info on where the issue can happened:
    1. Between the left side of the core to the left side of a macro (a small area for buffering and JTAG cell)
    2. Between the right side of a macro to the right side of the core (a small area for buffering and JTAG cell)
    3. on the left and right side of the macro
    4. A single row betweent two macros (at the right side of these rows)

    Regards,
    Eng Han


    Originally posted in cdnusers.org by EngHan
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