AGND and DGND Short with 0 ohm resistor.

[rajeshmp80]

Hi,

I have seen some schematic analog groung (AGND) and Digital Ground (Dgnd) short with 0 ohm resistor.It may get shorted.May I know the reason?

 

[goldsmith]

Dear rajeshmp
Hello
At first step i should say , that you can do short circuiting with each thing that you like ! and about digital ground and analogue ground . those grounds should connect together , but with star arrangement. do you know what is the star arrangement ? it means that those grounds connect together , just at one point ( digitals before that point are with together and analogs before that point are with together . and in that point they will connect together ) .
Best Wishes
Goldsmith

 

[shaiko]

0 ohm resistors are used to keep the option of a short ciruit.

If the designer decides to connect the points - the resistor is solderded and the potential between the points is 0 (short circuit).
If not, it's just left disconnected but the pads are there in case he changes he's mind.
Think of it as a jumper...

 

[marce]

To create a high impedance link between the analogue ground and digital ground....most experts on EMC etc reccomend ONE contigous ground.

 

[goldsmith]

Dear Marce
Hi
What do you mean by " to creating high impedance link between grounds " ?
Thanks
Goldsmith

 

[marce]

Adding a small resistor between analogue and digitalk ground or joining them at a via or a device pin adds a high impedance between the grounds, similar to the small gap formed by the waist of an hourglass. Not a good idea, the best way these days on most designs is to have ONE contigous ground plane.

---------- Post added at 18:22 ---------- Previous post was at 18:17 ----------

Some views (other than mine, as I was in the past a lone voice for ONE ground, and often derided for my views on this).
Grounding of Mixes Signal Systems
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http://focus.ti.com/lit/ml/slyp167/slyp167.pdf
http://www.ieee.org.uk/docs/emc1206a.pdf
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http://www.analog.com/static/imported-files/tutorials/MT-031.pdf