How to deal with layout of a chip that has both digital and analog circuits?

[yen]

My chip have two part.They are digital circuit and analog circuit.
How do I permute? How about gurad ring and power ring?
Which book or information can I read?
Thank you.

 

[nxing]

layout question

There are lots of books regarding the guard ring, check razavi's and Yannis's book.

Good Luck

 

[franck]

layout question

Hi,
The best separation is logically SPACE (I mean 100 or 200 um). It depends on your target of integration. You could separate these 2 part by an alternate NPNPN guarding block. If you have deep nwell you can also use it under your digital part. Be carefull some teckno doesn't allow to have a huge DNWELL.
By the way what kind af analog part is it? RF, analog, is there power ...

 

[uncle_urfi]

layout question

Explore what a double-split guard ring is.

Have separate pads for supply and ground.

Connect them on chip (this works for PLLs). But connect them in a distinct location on top-metal so that you can surgically remove them if you don't require them.

surgically=laser cutting

 

[vijay.kumarreddy]

Re: layout question

U can follow the following general guide lines:

• All the differential pars are protected with double guard rings

• All the sensitive signals are shielded from noise signals

• Each individual block is again provided with double guard rings

• Placed sufficient number of substrate and well contacts to avoid the
latch up

• For stress relief chopping of that long routing metal is done and it
is connected with other metal

• External metal filling is done for the die stress elimination

• All matched devices should be as compact as possible

• For common centroid matching in case of Differential pairs current
mirrors resistor matching and capacitor matching we have to
100 % . maintain symmetry to nullify the offset voltage effect

• Place as many contacts, vias as possible to reduce the
. resistance

• . Use top level metals for the power and ground signal routing

• . Avoid crossing of sensitive signals

• . Do not root the power signals in between the sensitive devices

• In order to avoid the substrate noise coupling to the diff pairs and
. other sensitive devices use guard ring technique

• - Place as many substrate contacts as possible to avoid the latch up
. problem

• . Use same orientation for all matched MOS devices

• A primary layout consideration is that the analog and digital ground
planes should not overlap So we have to maintain the separate
analog and digital vdd s and gnd s .

• In order to maintain a low impedance ground connection back to
, the system power supply it is usually necessary to use more than
. one connector pin for ground

• It is almost always necessary to keep digital runs away from
analog runs In worst case condition we can separate digital and
analog signals using proper shielding technique

• ( Do not use long metal routings especially metals connected to the
, ). gate of the Mos device which will cause antenna effect

• Take necessary precautions to avoid the EDS and Electro migration
. problems

• Use common centroid where ever possible which will nullify the
, ... . gradient stress effects

vijay

 

[mahendra]

Re: layout question

HI

The digital and analog blocks can be separated by TRENCH(TRIPLE WELL ISOLATION,DEEP N-WELL Etc),If ur process permits.

If ur process not permits any of the above,U can use N-WELL RING with more than 4 times the minimum width followed by P-type Guard ring.

The digital signal crossings over the analog signals must be SHIELDED.

Guardring also provides the protection from the noise BUT not much in the vertical direction.

Efficient guard ring design needs the following:

1.Width of the guard ring directly propotional to depth of penetration there by protection.

2.Spacing between the guard ring and the protected device.

3.Noise intensity & suceptability of the device to be detected & type of guard ring (single(N or p),Double(N and P)).


I would suggest Allen hastings to follow.All the best.

Regards
Mahendra

 

[Syukri]

Re: layout question

fOR ME IT START WITH UR FREQUENCIES....HIGH FREQUENCIES INPUT SUCH AS RF APPLICATION WITH NEED A GUARD RING... BUT IF IT'S JUST AN ANALOG PART, SEPERATING IT FOR QUITE A DISTANCE IS OK

 

[eda_freak]

Re: layout question

Read book by Alan Hastings on analog layouts....some chapters available on this forum....PM me if u are un-able to access...