Joining ANGD & DGND in one place???

[kousi_sen]

Hi,

We are using ferrite bead or 0 ohm resistor to join the AGND & DGND grounds in one place....

I would like to know which one is best...ferrite bead or 0 ohm resistor...

Pls help me

 

[Rame]

Hi,

The purpose of 0 Ohm resistors is to physically join, on the PCB, two nets
that you might want to track separately.

The use of ferrite bead and its limitation are clearly mentioned in the links given
below,please go through it for details.


http://www.sigcon.com/Pubs/edn/ferritebeads.htm

http://www.sigcon.com/Pubs/news/1_2.htm


Hope this helps you.

Regards

Ramesh

 

[cameo_2007]

Inductor is more effective.

Cheers!

 

[kousi_sen]

Thanks for ur reply..

Added after 10 minutes:

Ramesh,

you told that the purpose of 0 ohm resistor is to physically join.At the same time, ferrite bead produce some inductance...

And also we need to join both agnd & dgnd only...

Then why 'll choose ferrite bead instead of 0 ohm resistor

 

[cameo_2007]

to avoid the analog gnd noise getting interfered with the digital gnds.inductor acts as a filter.0E resistor is just a short

 

[kousi_sen]

I didn't get ur point..Pls explain me more..................pls

I'm new for circuit design...so i need a more information about how to choose the value of ferrite bead...
and
What is the advantage for using ferrite bead...

 

[cameo_2007]

have you chkd the link above given by Rame.
pls chk out that,u might get some hints.

 

[Rame]

Hi,

Cameo is right,firstly go through the links i have sent you earlier,then post your queries.The link i have sent covers all the question you have asked....

It seems you haven't gone through the links in first place,if you had you wont ask this question?


Regards

Ramesh

 

[sp_harikrish]

The ferrite will basically act as a filter. Which is basically eliminate the high frequency noise due analog circuits enters into the digital section.

If you shrot with the normal 0E resistor, you will not have any filtering circuit. The noise due to the analog circuit will get coupled into the digital circuit. So your output may detect by the digital can go wrong due to the threshold detected by the circuit.

Hence for better purpose short the analog ground and digital ground through ferrite is always a better choice.

SP_Harikrish

 

[BasePointer]

You should use 0 ohm resistor instead of a ferrite bead. Higher voltage differences between DGND and AGND at high frequency can cause components to damage.

 

[cameo_2007]

basepointer,
can u pls clarify your statement.
how is the frequency coming into picture.And if so,how is it damaging the component.


Cheers!

 

[BasePointer]

hi cameo_2007,

It will be problem when testing EMC EFT / Burst. If you look across this ferrite with a oscilloscope while testing, you can see high amplitude signals there that can cause components such as ADC has DGND and AGND to damage.