ground noise in pcb

Hello,

we have designed a board using aduc7026 microcontroller but we are facing noise problem as we have different grounds for Vref(gnd) , vcc(gnd),avdd(gnd),24gn connected separately to connector.I think noise problem is because grounds so please help me to come out of this problem.

Waiting for the reply
Regards
satish

It would be very nice of you if you could post the schematic of the board and everything that is connected to it including power supplies, along with the drawing of the board.
If you don´t, no one can help you.

ya analog and digital gnd are separate as i mentioned all the grounds are separate but still noise is generated.i think the problem is because i have not connected all gnd in a star.since modifying gnds is difficult because pcb is manufactured.Please me help me.

Thanks & Regards
satish

I think a schematic is in order.. per the above request by Kubeek..

I think a single post is also in order.

http://forum.allaboutcircuits.com/showthread.php?p=506235#post506235

Lundwall_Paul said:

Do not connect analog grounds (noisy) to digital grounds. The noise from the analog will be coupled right to the digital side.

Click to expand...

You have to connect the two grounds together at some point (single point ground) if there is any exchange of signals between the analog and digital circuits (which there usually is). The trick is to do the connection at the right spot.

And you have it backward. It's the digital ground that is typically more noisy than the analog.