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Analog + Digital Ground or just only a general Ground plane in high speed designs?

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flote21

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Hello guys,

I have reading some documentation in internet and some people recommend to use two different ground planes (AGND + DGND) but other people recommend to use just one good GND plane with the digital part and the analog part very well placed and differenced.

In my last designs I have been using only one ground plane and I placed the analog part and the digital part in the right way.And I got good results (I follow the next TI paper: **broken link removed**),

However, I would like to know which are your experience?

Thanks too much.
 

Hi,

reading design note is a good start. Knowing different techniques and the understanding of the effects is more important for a good result.

In practice there are often limitations where you can not use the "best" solution, but you have to do some compromise.
And sometimes a good placement and a cut in the ground plane to sperate noisy from high precision GND is as good (or even better) than a bad placement and having two seperate gnd layers.
I´m more in high precision / low noise analog circuits than high frequency circuits.

So for high frequency there may be other forum members with more experience than me.

Klaus
 

In general you can often use a split analog/digital plane instead of two planes on different layers.
The split plane (typically connected together at a single point) helps keep the digital ground currents away from the analog circuits. That also helps force the physical segregation of the digital parts from the analog parts.

That's usually better than using the same plane for both analog and digital circuits, although good results are certainly possible with careful layout and consideration of where all the digital ground current paths are.
 

mmm I see that there is not a general rule....Does anybody has an updated paper/documentation to have a look about this issue?

Thanks.
 

I think that I did not explain very well. What I would like to know if using just one GND plane for Digital and Analog devices is ok or it is better to use always different GND for analog and digital devices. See the picture attached. Which is better option 1 or 2?

Thanks. GND.jpg
 

Hi,

Sorry, if i was not clear. With my opinion
And sometimes a good placement and a cut in the ground plane to sperate noisy from high precision GND
Click to expand...

I wanted to prefer your option2.

Klaus
 

Thank you very much KlausST!

Do u know any good PDF or document to read about this issue??

Thanks!

KlausST said:
Hi,

Sorry, if i was not clear. With my opinion


I wanted to prefer your option2.

Klaus
Click to expand...
 

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