agnd dgnd
You can use small inductors on both AGND-DGND, and Vd-Va and different values of capacitors (1n, 100n, 10μ, ..) to cover wide frequency range.
Another method of separation DGND from AGND is to use quite thin truck to join them in only one point. In fact his short and thin truck acts as a small inductor.
Example here (page 3):
http://alpha.dyndns.org/ov511/downlo...1.0_060600.pdf
i always confused about DG and AG,
in AD's pll applications DG and AG connected together?
it is different?
Well.. I just got finished redesigning my pcb to handle this exact issue... Basically all I did was to make sure that the analog had a seperate ground wire all the way back to the battery or power supply.. and the digital can share ground with other digital iCs/uCs.
I also added some decoupling caps.. .1uf, 1uf, .01uf very close to the power and ground of all my iCs.. this will help with brown outs
I believe the first thing I mentioned fixed my issue.. but I just did both at the same time.. ebcause both are good practices.
Hope that helps some :)
Lee
DGND is a "noissy" signal (it is not perfect 0V, but has "ripples" around 0V due to switching of logic circuits)
Analog circuits on the other hand, are very sensitive to noisse.
Therefore AGND must be keeped "clean" (little ripples around 0V).
If you have a single batery, you are forced to short-cut AGND with the noissy DGND.
You can insert a LPF between DGND and AGND to keep noisse coupling from DGND to AGND small.
LPF can be made using C, R and/or L .
Important is to keep AGND clean!
Thanks, that was helpful, but when a LPF is added to the grounds it has its own voltage drops and if L is to be very high it will also have a high DC resistance and thats also a problem for portable low power systems!
Is there any reference document available, for the PCB AGND short-cuts or a practical LPF actually implemeted for such application.
The correct selection of the inductor values for ground separation is also critical. It may even the case worst. "one-point" ground techniques should be more applicabled.
The following Application Notes should be helpful.
You can use small area of copper to join agnd and dgnd for separation. Pay attention to the current flow. The small area of copper should connected to the battery in shortest path
eecly
please check my reply for this post earlier
https://www.edaboard.com/viewtopic.p...708&highlight=
the documents
read this --> http://www.hottconsultants.com/techt...gnd-plane.html
regards,
newbie
i have seen ppl using ferrite beads for proper isolation of noisy digital gnd from analog ground. Can you recommend what should be the specification of bead used. in terms of resistance. i am using this to seperation of a motor driver circuit from a mic4ocontroller interface