Shared contacted diffusion in layout

[anhnha]

I am confused about shared contacted diffusion in CMOS layout.
Is it possible to use shared contacted diffusion for two nMOS transistors with different widths?
BTW, two nMOS and pMOS transistors are never shared contacted diffusion, right?

 

[analogdesign]

Yes you can share a diffusion between devices with different widths, that is no problem. One device extends farther than the other. In fact you should share diffusion as much as possible to reduce parasitic capacitance.

No you can't share diffusions between PMOS and NMOS devices. This is because the diffusions are different doping types! (in other words they are not in the same well). You are correct about that.

 

[anhnha]

Thank you.
I am learning about analog design. Hope you could help!