guard type and guard rings

[fofo]

Hello,

What is the difference between the guard type and the guard ring?

1. I think the guard type should be Nwell for a PMOS and substrate for the NMOS. But what about resistors (rpoly2 for example)?

2. What is the difference between Diff and cont choices for the guard ring???

Thanks a lot

 

[Dominik Przyborowski]

Resistors could be placed in substrate or nwell so You have freedom to choose.

 

[dick_freebird]

Poly resistors sit above the silicon, not in it, and have no
need for isolation wells / ties. Although in some cases a
driven well below, might be good for isolating substrate
noise or whatever.

The guardring generally follows the periphery of the active
region, ensuring a uniformly-low-impedance contact to
the entire well (enforced by minimum distance rules). The
guardring may be simple, same-species (ohmic only) or
may be compound, concentric, opposite-species in the
interest of additional latchup supression / minority carrier
collection.

 

[fofo]

First of all, thank you for your answers,

The guardring generally follows the periphery of the active
region, ensuring a uniformly-low-impedance contact to
the entire well (enforced by minimum distance rules).

I'm not sure but it looks impossible to enroll a transistor with a guarding and still be able to put vias or what ever to power feed it for example..???

 

[dick_freebird]

The guardring does not need continuous metallization (but
as much as possible, helps a bit) and in any case you could
drop down from above (Met2/Via). In many cell libraries Met1
is pretty much blocked anyhow, guardrings aside.

Don't overthink it.