[SOLVED] Does the distance between a transistor and its dummy matter?

[ElieKhoury]

I am designing an IC and in the layout I have to make a decision on whether I move a dummy transistor away from its main transistor and closer to the surrounding bulk, or I keep the dummy close to its main transistor. Is there any consequence or benefit to either option?

 

[dick_freebird]

It depends whay you want from the "dummy".

If it's meant to improve uniformity in a multifinger device
wired as a mirror or diff pair, then the "dummies" should
be the endmost fingers of that same active area.

If it's more of a "spare" and not particularly matched to
anything, then you can put it anywhere.

If it's supposed to allow you to strap on 2X the gm, then
it's probably meant to match Mr. 1X and may want to share
the same active (and then both of those might get outboard
dead fingers, so that -if- it's employed, it's already set up to
match as well as possible.