Questions about analog power rings

analog power ring

when chip have analog block and digital block ,need two power ring , one for analog and the other for digital. Does the two power ring need shield? And the analog block is small, the analog power ring just around analog block? every analog block must need guard ring? thanks!

Re: analog power ring

Hi stormwolf,

Normaly, Marcos(Analog) have power rings around them.

Re: analog power ring

analog power ring let core (digital) is free from noise from analog part.

analog power ring

I have see some training course, and i see that at those training, analog power connect to digital power , and i'm confuse that all book said that analog power should avoid connect with digital power to avoid noise. Does i need to add a analog power ring around core ?

Re: analog power ring

Hi,

It is common for analog IP to have guard rings inside it. A guard ring protect the analog IP from digital nosie. It is also important if the analog IP is operating at different voltage. The gaurd ring consists of diffusion, well and metal (usually metal 1).

For mix signal layout, it is not necessary to run a power (metal) ring around the analog IP. You do this if you need to supply power to the IP, and not for isolation. However, it is good to keep a gap between between the analog IP and the digital layout. Note that this is not always necessary as the design of the IP might have a wide guard ring around it, and thus the digtal layout cannot get close to the analog circuit.

There is also concern of the pad power ring (this is the pad power that drive the digital output, and also for ESD protection). It is a common practise to break the pad power ring between the digital and analog domain. Break it physically or with a diode-breaker cell.

Obviously, the power has to be connected eventually. This is usually done on the PCB. The futher away this connection , the better the power isolation.

So, there are quite a few type "power ring" we are talking about. They are different and should not be confused in a discussion.

Regards,
Eng Han
www.eda-utilities.com