Hi,

I am designing a mixed signal PCB. I have to sample an analog signal with an ADC and send samples to FPGA for processing. I read a lot about mixed signal PCB layout guidelines on internet and came out with a power supply and grounding scheme. Can you please check and tell
whether my layout (attached below) will be good enough to prevent high frequency digital currents from the digital ground plane to corrupt sensitive analog signals over analog ground plane.

I have made sure:

1. No trace crosses the split (MOT) between digital and analog ground planes.
2. There is no secondary ground plane and chassis contact point except at the input supply point.

I have one doubt:

Should I put input supply connector (+12V, Chassis ground) on digital ground side or analog ground side?

Thanx.

-Vipin

 

I uploaded the layout scheme.

 

Should I put input supply connector (+12V, Chassis ground) on digital ground side or analog ground side?

The way you have it now the analog side sits on top of all the digital ground noise. I'd put it on the other side.

 

Thanx for the reply but dont you think if I put connector on the left side digital currents will flow from digital plane to input supply ground (chassis ground) through analog ground plane (as there is only single path) and currupt all my analog signals. On contrary if connectors are on the digital side digital currents will be limited to digital planes and find an easy path to chassis ground.

 

OK, it's a toss up which is the worst side to put it on. So put it in the "middle" meaning join analog and digital grounds at the power input no matter where it is physically.

 

I too am thinking so.. that it would have been best to join both in the middle near to power supply. Unfortunately I have sent it for fabrication and at this stage I cant make changes . But I have had provision for putting jumpers around the MOT if any difficulty encounters.