Dear Forum Members,

For applications involving both Analog and Digital chips on the same board we make use of separate AGND and DGND [ ground planes ] and also sometimes for more precision stuff we use separate power planes.

When laying out separate ground planes we take care that all the analog signal traces have AGND under them and all the digital signal traces have DGND under them. The two planes are separated from each other and join at on and only one place often under the ADC or mixed signal micro controller.

For laying the separate ground planes it is very convinient if all the analog function related pins lie on one side of chip and all the digital pins on the other side(s). Lets take example of C8051F12x or ADuc8xx these micros have all the analog related pins on one side and this makes laying separate ground planes very convinient as shown in figure below. [ Analog related pins are AGND, AVcc, Vref, ADC inputs etc. ]



Now the real Problem... Some of the newer chips such as LPC2124 [ ARM ] as shown in figure above have the anlog function related pins scattered on two or more sides with some digital pins in between them and not on the same side. How to lay separate ground planes AGND and DGND in such situations?

Thanks to all the forum members for reading my post.

Regards,
Prahlad Purohit