Common Centroid Capacitor Layout in Cadence

Hello,

I am trying to do a common centroid layout pattern in Cadence using MIM caps.

Does anyone have any screen shots of an example of this type of layout in Cadence using MIM caps or a resource (book, paper, course notes) that would be helpful in what this would look like ?

It is for a fully differential OTA for switched capacitor applications, so it has an integrating and sampling capacitor.

Thanks.

Here's a layout for 4 equal MIM S&H and feedBack caps C1..C4 for a diff. S&H OTA - divided into 8 single caps, each:

C5 & C6 are used as couple caps from the outputs to the CMFB circuit; the 2 "D" caps are dummies.

Instead of dummy caps around all sides, an adapted MT & M3 guard ring had been built, together with passably equal lengths (cap-values) of the 2 nodes to the input gates:

Erikl,

Thank you for your message.

What are the advantages/disadvantages of this technique versus dummies all around the sides ?

Thank you.

- - - Updated - - -

Erikl,

You said C1...C4 are 4 equal MIM S&H and feedBack caps C1..C4 for a diff. S&H OTA.

So which capacitor is which ? C1 is sampling, integrating capacitor ? C2 is sampling, integrating capacitor ? C3 is sampling, integrating capacitor ? C4 is sampling, integrating capacitor ?

It might not matter, but just wondering to picture it in my mind.

Also C5, C6 are part of the Switched Capacitor CMFB circuit ? or just dc/ac coupling to the CMFB ?

Thank you.

Puppet123 said:

What are the advantages/disadvantages of this technique versus dummies all around the sides ?

Click to expand...

Advantage: Less silicon space. Disadvantage: Geometry and spacing have to be chosen thoroughly.

Puppet123 said:

You said C1...C4 are 4 equal MIM S&H and feedBack caps C1..C4 for a diff. S&H OTA.

So which capacitor is which ? C1 is sampling, integrating capacitor ? C2 is sampling, integrating capacitor ? C3 is sampling, integrating capacitor ? C4 is sampling, integrating capacitor ?

Click to expand...

Doesn't really matter: They all are the same size. Two of them for S&H, the two others for feedback.

Puppet123 said:

Also C5, C6 are part of the Switched Capacitor CMFB circuit ? or just dc/ac coupling to the CMFB ?

Click to expand...

The latter: diff OTA outputs ac coupling to CMFB input - as already mentioned above.

"...Instead of dummy caps around all sides, an adapted MT & M3 guard ring had been built"

What is MT and M3 guard ring - M3 is metal 3 - what is MT ?

Thank you.

Puppet123 said:

what is MT ?

Click to expand...

Top metal.