[Magic-dev] Extraction of cross coupling caps with shielding

[Graham Petley]

Hallo,

   I have found out that Magic extraction does not take account of shielding
when calculating cross coupling capacitances between metal wires. Take the
example below (you need to view this with a monospaced font). The numbers 1 and
2 are metal wires 1 and 2, and the letters S are a shielding wire. In the left
hand example wire S is shielding metal 1 from 2. In the right hand example it
is not.

  111111111          111111111

  SSSSSSSSSSS        SS

    22222222222        22222222222

I find that the cross coupling cap between 1 and 2 is the same. What changes is
the cross coupling caps between 1 and S and 2 and S, which is lower in the
right hand example.

I'm using a Magic technology file that I wrote myself, so this could be the
source of the error. But before I start investigating, I wondered if anyone
could confirm how Magic should handle the extraction of cross coupling caps in
the above situation.

I'm using Magic 7.4 revision 33.

Best regards, Graham Petley