how to use pruneDevice for pmos4

[Ck seok]

In divaLVS rule file, I added "pruneDevice(MOS ("pmos4" "nmos4")) to prune
dummy transistors.

I mean that dummy transistors are transistors with D, G and S connected
altogether.

"Mos4"s with drain, source, gate and bulk connected altogether were pruned.
However, mos with only drain, source and gate connected altogether was not
pruned.

How can I prune those dummy transistors?

One more thing. Are there any other reasons we use dummy
transistors except "etching issue"?

 

[G Vandevalk]

Ck seok wrote:

In divaLVS rule file, I added "pruneDevice(MOS ("pmos4" "nmos4")) to prune
dummy transistors.

I mean that dummy transistors are transistors with D, G and S connected
altogether.

"Mos4"s with drain, source, gate and bulk connected altogether were pruned.
However, mos with only drain, source and gate connected altogether was not
pruned.

How can I prune those dummy transistors?

One more thing. Are there any other reasons we use dummy
transistors except "etching issue"?




pruneDevice can omly be used with devices that have all nodes shorted

together.

MOSFETS are often used as capacitors (i.e. S & D shorted, G to BULK is
the capacitor.)
or simply as TURNED OFF MOSFETS (i.e. G shorted to BULK) Both of these
devices are
often treated by circuit designer as being something other than MOSFETS.

The S/D shorted mosfets can be extrated as separate devices. (do not use
the physical keyword
and code both cases as device lines to separate devices.

Also an odd formed mosfet can be created by a Y shaped gate. This should
be avoided or declared evil.

YMMY

-- Gerry

 

[Ethan Dawe]

One more thing. Are there any other reasons we use dummy
transistors except "etching issue"?

Dummy devices may also be added to be used as a "spare." During a metal spin
it could be rewired to nearby parrallel devices.

Ethan