Hi Khaled,

        As a board designer I always encorage keeping the grounds as seperate gnd
net names in you schematic.  This precludes any miscommunication between
you and your layout person and will help them give you the best component
placement.  We often have mutiple analog ground "islands" on the board
which make such seperate gnd net names even more important.
        Usually a ferrite bead or 0 ohm resistor is used to merge the ground nets.
 Your application data on your A-D chip often specifies the location where
the grounds should merge.
        If any tracework traverses the split between these ground areas, care
should be taken route traces at or near the point where the grounds merge
to optimize the signal return path.

        Regards,
                Dave












At 08:50 PM 8/5/99 +0300, you wrote:
>Dear fellow designers,
>I am working now on a design with a mixed signal ,i.e. analog and
>digital.
>What I understand is that ,from the EMC point of view ,you have to
>separate between the two grounds, the analog ground and the digital
>ground. My question is how are you going to connect them at the end,
>directly (short circuit) or through a component (e.g. ferrite bead). One
>of the reasons I want to do that, is to know if I have to separate the
>two grounds right from the beginning,i.e. on the schematic, or shall I
>leave it till the layout and then keep it in mind to connect them
>directly. And what is the preferable grounding scheme for that type of
>designs.
>Any help is appreciated.
>
>--
>Best Regards
>Khaled H. Fouad
>PCB Designer / R&D Department
>Tel.: +20 (11) 333414  Ext. : 312       Fax.   : +20 (11) 335613
>BAHGAT Group    http://www.bahgat.com
>Email  : [log in to unmask]
>Second Industrial Zone, Plot 240, 6 October City, Egypt
>
>
Dave Graves
Design Manager
UltraCAD Design
http://www.ultracad.com