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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

  • Hello Friend ,
    How about using the below options -fixedGap with addWellTap :

    If not can you move your Macrocells accodingly to align .


    Examples
    The following command preplaces a well-tap cell xyz on every row in the floorplan, with the distance between two consecutive cells not exceeding 40 µm.

    addWellTap -cell xyz -prefix welltap -maxGap 160 -fixedGap 40

    And you can add option : -fixedGap


    FYI.

    -fixedGap
    Ensures that the specified gap is always maintained. That is, this will not search for a legal location if it cannot place well-tap cells at the given -maxGap. Instead, it goes on to place well-tap cells at the next position.

    -maxGap microns
    Specifies the distance, in micrometers, from the right edge of one well-tap to the left edge of the following well-tap in the same row. If well-tap cells cannot be placed at this gap due to placement blockage, placement will search for a legal location: first towards the previous well-tap, and then away from the specified location. Under no circumstances can the gap between well-taps be less than 45% of the specified maxGap value plus the well-tap width. The distance is measured from the center of the cells.


    Originally posted in cdnusers.org by mohanch007
Reply

  • Hello Friend ,
    How about using the below options -fixedGap with addWellTap :

    If not can you move your Macrocells accodingly to align .


    Examples
    The following command preplaces a well-tap cell xyz on every row in the floorplan, with the distance between two consecutive cells not exceeding 40 µm.

    addWellTap -cell xyz -prefix welltap -maxGap 160 -fixedGap 40

    And you can add option : -fixedGap


    FYI.

    -fixedGap
    Ensures that the specified gap is always maintained. That is, this will not search for a legal location if it cannot place well-tap cells at the given -maxGap. Instead, it goes on to place well-tap cells at the next position.

    -maxGap microns
    Specifies the distance, in micrometers, from the right edge of one well-tap to the left edge of the following well-tap in the same row. If well-tap cells cannot be placed at this gap due to placement blockage, placement will search for a legal location: first towards the previous well-tap, and then away from the specified location. Under no circumstances can the gap between well-taps be less than 45% of the specified maxGap value plus the well-tap width. The distance is measured from the center of the cells.


    Originally posted in cdnusers.org by mohanch007
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