Difference b/w NWELL and Deep NWELL

[vikramc98406]

Can anybody give me the,
Difference b/w NWELL and Deep NWELL.

I heard to control noise b/w Analog and Digital section of a SOC,
use of deep NWELL is use.

someone can can giv more info on how does this works

 

[none34]

nwell process.all of the N mos share the P_sub as bulk.
DNWELL will isolate N mos's bulk from P_sub.
If two N mos in two different DNWELL.their bulk is not connected.

 

[salma ali bakr]

it's used for isolation between digital and analog parts...because the digital parts operating at high frequencies may leak minority carriers in the substrate, which can affect the nmos transistors of the analog parts...

 

[sunjimmy]

The conventional Nwell is shallow. So if there is any noise injected into P-substrate, it's MORE easy to bypass the conventional N-well guard ring. But the depth of deep-Nwell is larger, so for the noise injected into P-substrate, it's more difficult to bypass the Deep-Nwell guard ring. Because noise need to travel longer path to cross Deep-Nwell to affect sensitive ckt. So usually Deep_Nwell is used to isolate the noisy digital ckt from sensitive analog ckt.

 

[vikramc98406]

sunjimmy,

As per your explanation, i would think,

instead of deep nwell a wide normal nwell would be preferable to have
long path for the noisy signal to cross.

in case of DEEP nwell i think noisy signal can still cross

 

[sunjimmy]

Usually analog desingers use wider Nwell guard ring to isolate sensitive ckt if there is no Deep Nwell in process option.
But if Deep Nwell is available, it's better than conventional Nwell guard ring in terms of same guard ring width.
Deep Nwell isn't free. In fact, extra layers are needed to form it, so the wafer price is a little bit higher.

 

[mbyoussef]

This issue has been discussed before here: