Noise problem 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

"Ground" isn't really fixed, there is always some impedance in the lines even if you make a "ground plane." So plan to make the bouncing grounds just bounce relative to themselves by carefully joining then together.

Best way is to make a "star" connection where these three signals all meet at one single point. As an alternative, Vref(gnd) and avdd(gnd) can join at one place, then this junction meets vcc(gnd) elsewhere where it is convenient.

Also, the first time I used a reference regulator chip I got surprised at how much cap these things need at their outputs: they are quite noisy until you add as much cap as the data sheet says to add.

thanks for the reply.

since pcb is manufactured and testing is in process.So again modifying design(ie making ground in a star connection) and manufacturing the pcb is time consuming and difficult process so can u please suggest other alternative idea to overcome this problem.

waiting for the reply

Regards
satish

I think you've got another thread going in one of the other forums for the same topic.. In that forum Kubeek asked for a schematic.. It's hard to help w/o it..

Caps. Add lots of caps at the power points.

You may want to cut the grounds to the Vref(gnd) and avdd(gnd) and jumper them into a star.

Also do make sure the Vref all by itself is clean on the scope. One probe, + and - leans direct on the +Vref and -Vref.