Hi Suresh,

First of all, what is the common salutation in Hindi? Just curious.

Second, The first thing you should do is simply segregate the signal traces into separate regions of the board. The return current from any one trace will try to follow that same trace, will try to stay directly under it, in the ground plane. This is because that is where the impedence between the trace and ground plane is lowest.

So if the traces are segregated, so will be the currents. It is extremely rare that anyone actually needs to physically split a ground plane into digital and analog parts. I know that every DAC manufacturer says that you should. Not to put too fine a point on the matter, but they're lying.

But if you really are that unlucky soul who has so offended God that He has punished you and you really do need to split your ground plane, then there is one peril that you must either understand or rely on dumb luck to avoid. Never, make that NEVER, let a trace cross the split. Has anyone here ever worked with microwave transmitters? Can you say "slot antenna?"

As I mentioned earlier, the impedence of the trace depends on the distance between it and the ground plane. When a trace crosses a split in the plane, it experiences an impulsive increase in impedance. This causes an abrupt change in velocity (an acceleration) of the electrons, and as everyone knows when you accelerate an electron you cause it to emit electromagnetic radiation.

These impedance impulses will cause your circuit board to spew EMI. They will also cause reflections and interferences, for both digital and analog signals.

The bottom line is that if you do split your ground plane, you absolutely better keep the traces segregated. And if you can do that sufficiently, then you probably didn't need to split the plane in the first place.