Help needed! can I connect cycloneIII's GNDA with digital ground?

Altera recommends: "The designer should connect these pins to an isolated analog ground plane on the board." But, to be honest, I do not know of many boards that have been built according to this rule. Often, a single ground plane is used and this works. Personally I recommend paying attention to the negative pads in the ground plane caused by signal vias. If these negative pads are too large then the remaining track width is small what causes inductance. The effect of this is worse that that one caused by a common GND net.