Opinion regarding Layout detail

[AMSA84]

Hi guys, I'd like to ask you, who might be more experienced in layout, which of those two ways to connect the drain and gate of a mosfet (for an inverter chain) is more advisable:



Orange or White?

Regards.

 

[chris.mourad]

Hi

The difference I see between orange and white if I understand well, is the number of vias.

Increasing the number of vias will decrease the parasitic series resistance that the via present. In some technos, you can have very high vias resistance so this might be a good idea. At least I don't see any counterparts

 

[AMSA84]

Thanks for the reply chris. I should have been more clear. What I meant was the way that the connections are done (not the number of vias).

Thanks.

 

[chris.mourad]

Hi

I am not sure that the layout on the right is correct, as it seems there might be a short between drain and source of the transistor.

Is this what you are asking? Otherwise I am getting a little bit confused on what you are looking for...

 

[AMSA84]

Chris, with all respect, how can you say that they are shorted? It is an inverter. The drain of the PMOS AMD the drain of the NMOS are the only metals shorted.

 

[andre_luis]

Do not consider myself knowledgeable on the subject despite having studied ASIC design many years ago and it is clear the pattern of field effect transistors there, but I think it would help if you put the legend of colors of both metal and positive/negative polysilicon layers - unless that is standardized.

 

[chris.mourad]

Hi

It was just an impression, the colors did confuse me.

 

[DharmaSlice]

well first point is its always better to have an even fold, this will have matching better (I know its not important in an inverter, just good practice, if you needed to increase the strength or add in dummy devices)

 

[dick_freebird]

What do you want from this inverter? If it's fast risetime
then minimizing poly length (Rg) is a good idea, favor the
"orange" (or maybe even contact both ends) style.

But making edges that don't need to be fast, faster
doesn't buy you a lot besides trouble of various sorts
(EMI, supply bounce, etc.).

Is this a problem that really deserves a lot of thought?

 

[AMSA84]

Yeah, I want fast risetime and falltime. However, if I adopt the orange style, the poly width of the mosfets will be larger. Isn't bad?