Cadence Virtuoso Layout & Multiple grounds

[Emanuele]

Hi everyone, i'm developing a layout using Cadence virtuoso and i have this problem:

My circuit is composed by shift registers and an analog circuit, so i need to use 2 "Vdd" and 2 grounds, the problem is that obviously i can only connect one of those grounds to Bulk, while i can easily give different potentials to different nwells. This causes me to have some Nmos transistors to have different grounds for sources and bulk....

Is there anyway to avoid this? i mean, is there anyway to have 2 diferent bulks voltages in same circuit? :/

I'm looking for any kind of solution thank you in advance ;D

 

[AdvaRes]

Hi Emanuele,

Using 2 Vdd is logic. But why 2 GND ?

 

[Emanuele]

hehe ask to my professor....

im making a degree work for him and he wants to use two different vdd and grounds for digital and analog parts of the circuit...

do u think that there maybe any solution? other that make him change idea? ^^

 

[AdvaRes]

What is the Voltages of your power supplies ? Is there a big difference ?

 

[Emanuele]

For Vdds they should both be 3.3V.... For the usage im going to make of thsi circuit, but since it could be used for other purposes too, they could one day be different... even of 2V....

For the grounds i obviously need them to be separated to prevent any "cross-problem" from digital to analog parts and viceversa...

 

[gld]

Your fab may offer a deep N-well option that can do this.

With this, you can put NMOS in isolated P-wells, which are themselves implanted into deeper, isolated N-wells in the P-substrate.

Of course, this adds cost.

 

[Fady Atef]

Hi Emanuele,

You can use different gnds (multiples ground) in your design , with out using DNwell :!:. :idea: You will use a logic layer known as PSUB2 and place it around one of the two grounds you have, and it will lead you to pass LVS

Thanks And best Regards
fady