ANalog and Digital gnd

[smith_suez]

how do we effectively couple/short analog and Digital gnd in a PCB ?
Thanks

 

[qasmi]

Good question, the answer to this question will help me too.

Regards

 

[Rame]

Hi,

Check this link from edaboard,



http://www.analogzone.com/acqt0407.pdf

This link below will be very useful and it also differentiates and purpose of coupling both the grounds.For subsequent queries relate to that,there are other links too or simply search in the edaboard itself,you shall get many articles.

http://www.epanorama.net/wwwboard/messages/1942.html


Regards

Ramesh

 

[Anonymous_Ricky]

hi,

ferrite beed is generally used to short AGND and DGND planes in a pcb.

Regards,
Ricky

 

[Rame]

Hi,

This topic has been discussed earlier,here is the thread,check this out...




Regards

Ramesh

 

[A.Anand Srinivasan]

as far as i know ferrite beads contain a lot of inductance and ground bounce is mainly due to surge of current through inductance.... how would connecting analog ground and digital ground using inductance be a good solution.... pls explain...

 

[smith_suez]

Thanks a lot everyone....
Then how wud we route a trace if the trace has to pass through 2 Planes with different Nets in same/different layers...

 

[Rame]

Hi Anand,

If ferrite bead isn't a ideal for coupling the grounds,then you please shed some light which is the best way to couple..???


If you go the thread i have attached,it discusses about the coupling.

Do appreciate,if you could send your views too..


Check this link suez for the routing techniques,

http://www.hottconsultants.com/pdf_files/june2001pcd_mixedsignal.pdf




Regards

Ramesh

 

[A.Anand Srinivasan]

I visited that post.... i found that another person had specified ferrite beads but the justification against the inductance has not been given there....

 

[Rame]

Okay,then your version of analogy,latter we can have a consolidated conclusion over the issue..

hope you understood


Regards

Ramesh

 

[Rame]

Hi,

You have told justification isn't given for the inductance,can you shed your views over the issues,let us also know your thoughts.


Regards

Ramesh

 

[brmadhukar]

For the DC we need both AGND and DGND should be equivalent. For higher frequencies we need AGND to be undisturbed by DGND.

So use either a thin line or inductor between the AGND abd DGND and use separate decoupling capacitors.

Hope this helps.
BRM

 

[A.Anand Srinivasan]

i think the above post explains things well.... because digital ground is gonna experience high frequency disturbances due to the switching and inductive beads would take care of that.... the separate decoupling capacitor would take care of the low frequency behaviour.....

 

[pinoy]

A very small trace that will connect both GND

 

[cyberrat]

create a part that is basically a short, (SMT resistor with pads shorted) connecting Agnd & Dgnd to each pad wont throw up an error in your CAD program but will provide the short needed.

It obviously gets left out of all pick & place programs etc.

OR do it with a zero ohm link component, that way when fault finding the link can be removed.