isolation between analog & digital ground

[dipak.rf]

How do i isolate my digital and analog ground on same substrate?

Description: i have mixed signal design with analog and digital blocks, now i have to separate or isolate my digital VSS and analog VSS. but my problem is substrate will be same.

 

[keoiuser]

you can use different ground for analog and digital for example gnda for analog and gnd for digital

 

[Old Nick]

The grounds will always be connected through the substrate. The substrate has a fairly high impedance though. I recently measured around 90ohm between pins only connected through the substrate on a chip we made. Current will generally take the path of least resistance, which will be through the metal layers and off the chip. Do keep the grounds seperate on the metal layers though.

 

[layoutmaster]

Your GNDs will be ALWAYS connected to your substrate.

A good layout technique is to keep two (or more) independent GND lines, one will be connecting all the substrate contacts and the other(s) will be doing your actual chip GND connections. Then, all the "independent" GND lines will be connected (shorted each other) at the GND bond pad...

 

[jecyhale]

How do i isolate my digital and analog ground on same substrate?

Description: i have mixed signal design with analog and digital blocks, now i have to separate or isolate my digital VSS and analog VSS. but my problem is substrate will be same.

If you use P-sub process, I think you can use the P-well for the Digital circuit.

Or else, use three guarding ring will be P+, N-well and P+.