Re: how to use pruneDevice for pmos4

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