Virtuoso LAyout & different analog and digital grounds

[Emanuele]

Hi everyone,

I'm working on a circuit layout, it is composed by a digital and an analog part, so i need to use 2 different grounds, an AGnd and a Dgnd.

My problem is that i can obviously conect only one of these grounds to bulk...

Is there any solution?

Thank you in advance

 

[varma_cs012]

Re: Virtuoso LAyout & different analog and digital groun

Yes of-course there is a solution.

Generally we see this type of connections in each and every layout. Basically this problem we will see only with NMOS, as anyway PMOS bulks are always seperate!

According to the process you are using, you can do either ways!

1. If you are using a single well process and you are working with low voltage devices:

Between Two of your Digital and Analog Bulks use N-well guardrings to separate them in horizontal direction. In this way your substrates are still in Soft-connect with each other in vertical direction.

And almost all technologies use one layer called "PSUB" or "SEPGND" marking layer to define two different substrates.

2. If you are using a triple well (Deep_N_Well, HVPW, Nwell) you can simple put those two NMOS in different HVPWs!

If you have still doubts we can discuss futher!

BR, Varma!

 

[deepak242003]

varma is right.. you can used well guard ring to seperate different ground... be alert about more well to well spacing at different potential...

 

[Fady Atef]

Re: Virtuoso LAyout & different analog and digital groun

Hi,

You will need to use the marking layer "PSUB" to define two different substrates. you will use this layer to surround only one ground e.g. Dgnd.

But you have to know that is only marking layer to pass LVS, But if you are working on A product you must take care of Substrate noise Isolation Techniques.