Do PCells have their own DBU?

zlim

Hi Matthias,

I am drawing shapes in a layout that uses a DBU of 0.0001. I am able to draw rectangles on this grid, such as a 1.0001 by 2.0001 rectangle, but when I try to make a PCell, the DBU seems to be something larger. For example, I tried drawing a PIE from the Basic PCell library with radius 1.0001, but the resulting PIE radius was 1.000.

What do PCells use for their DBU? Is there any way to set it?

Thanks and regards,

Z Lim

Matthias

Hi zlim,

you can actually control the DBU the PCell uses. The layout will be converted to the DBU of the client layout when you reference the PCell library.

More precisely, the database unit is stored inside the host layout that is part of the library. The right place to change the database unit is the initialization of the library:

class MyLib < Library

  def initialize  

    # Set the description
    self.description = "My First Library"

    # initialize the database unit:
    layout.dbu = 0.0001

    ...

    register("MyLib")

  end

end

With this modification, you should be able to produce circles with sub-nm resolution.

Matthias