[Layout - Question] What's the best common centroid combination?

[gonsays]

Hello

I've been designing an OTA on CADENCE and I would like to perform the common centroid for the following transistors:



The original dimensions:
W14=55um ; L14=0.55um
W11=27um ; L11=0.55um

New dimensions (dividing M14 in 4 transistors & M11 in 2 transistors) for each divided transistor:
W14'=W14/4=55um/4=13.75um ; L14'=L14=0.55um;
W11'=W11/2=27um/2=13.5um; L11'=L11=0.55um;

On the following figure you can check them on the layout:



What would be the best combination for the common centroid (with 6 transistors total)? Is there a problem with the dimensions (13.5um vs. 13.75um) between the pair? Should dummies be used?

Thank you very much in advance!

 

[erikl]

What would be the best combination for the common centroid (with 6 transistors total)?

I'd suggest to put M11(1) between M14(1) & M14(2), and M11(2) between M14(3) & M14(4). Of course this will complicate the wiring, but it helps for better matching.

Is there a problem with the dimensions (13.5um vs. 13.75um) between the pair?

No - if this is ok for Id(M11).

Should dummies be used?

Not necessary, I'd say. But if you want to spring an extra for good matching, you could put 2 extra (grounded) poly structures on bottom and on top of the block, same dimensions and same spacing as within the block.

 

[t4_v]

I agree with erikl. You can use ABA ABA combination.

You can also think about: AABBAA if the routing in the first approach will be too difficult.


Regarding dummies, I would suggest using them due to the fact that you're doing common centroid layout and that rather means you would like to have nice matching. The dummies are very popular especially in lower technology nodes.