What's the reason for shorting AGND and DGND using Ferrite bead?

[psr]

Hi,

In mixed signal boards, we are keeping analog and digital grounds separated.
Whats the reason to short the two grounds at one point using Ferrite bead?
Can anybody suggest any good study materials to understand characteristic impedance , EMI, EMC, DFM ,DFTconcepts in little bit simple way?

Thanks,
Psr

 

[karesz]

AGND and DGND

Hi,
for referencing, you must have a common point, as DC system it has to be short, but as AC or HF system their are to separate: these is with some inductance ("ferrite bead L" is a wide band inductance/yoke) light to realize...
For exact infos Google pls: makes often wonder!.
K.

 

[bert_kak]

Re: AGND and DGND

Hi,

In mixed signal boards, we are keeping analog and digital grounds separated.
Whats the reason to short the two grounds at one point using Ferrite bead?
Can anybody suggest any good study materials to understand characteristic impedance , EMI, EMC, DFM ,DFTconcepts in little bit simple way?

Thanks,
Psr

We use ferrite beads between these 2 grounds so that the noise coming from the digital area won't add up to the noise in the analog area and vise versa.

 

[loosemoose]

AGND and DGND

one point to remember is that you don't want to cross any signal between the GND's. IF you do that will increase your noise dramatically.

you may find some stuff on Ott's webpage
http://www.hottconsultants.com/