A problem about guard ring,really confusing!!

[reneezl]

I know that guard ring is used for shielding. Ptap guard ring is used for NMOS and connected to VSS, while Ntap guard ring is used for PMOS and tied to VDD.

But I do not know how to draw a double guard ring?

1,Should I put the Ptap guard ring inside, and Ntap guard outside, or vice versa?

2,When it comes to mixed-signal ICs, should the sequence of guard rings be different for digital and analog part of the layout?

Thanks in advance!

Renee

 

[viren_s]

hello..

if you have to put doubble gaurd ring- if it is nmos put ptap gaurdring first then ntap and vice versa.

In mixed signal gaurd ring is added in analog ckt to isolate if from the noise generated by the digital ckt.

Gaurd ring is same digital or analog. Usually we dont require in perfect digital ckt..

Regards,
viren

 

[reneezl]

Thank you for your reply!

But the double guard ring is not for just nmos or pmos. Actually, I only used single guard ring for them(eg. ptap ring for nmos, ntap ring for pmos), while the double guard ring is for the whole module such as opamps.

So, under the above situation, which sequence of ntap and ptap guard ring should I use?

Thanks!

 

[dick_freebird]

You put the body-species ring closest to the S/D and
the counter-species outside it. Otherwise there is
some chance of field-FET leakage from the S/D to
the same-polarity ring.

 

[reneezl]

You put the body-species ring closest to the S/D and
the counter-species outside it. Otherwise there is
some chance of field-FET leakage from the S/D to
the same-polarity ring.

For an opamp that contains both pmos and nmos, how can I choose the body-species?

Thanks

 

[snafflekid]

You put all the nmos in one body tub and all the pmos in another body tub. Place a body pickup ring around each tub and then a substrate tiedown ring around the whole thing.