I am designing a PCB for an image sensor. The manufacturer provided a design guide in which they recommend using multiple split ground planes.
One ground plane is for the analog supplies, but there are two split digital ground planes: one for the high speed serial data interface (bandwidths to 4GHz) and one for the rest of the (slower) digital interface signals (bandwidths up to the 10s of MHz).
I think I can understand the necessity of the split analog ground, however why would you split digital grounds? Shouldn't return currents be confined underneath the traces at such high frequencies? Is this to try to keep away the return currents of high speed interface (SLVS differential signals) from the interface signals, or the other way around: keeping the return currents of the slower single ended signals away from the differential interface?
Can I connect the two digital grounds a bit further away (before decoupling capacitors)?