Can anyone tell me the different between analogue and digital ground and how do i know which components are fall under which side??
That is a question which is bigger than this forum. You can have many nets called by many different "ground" names. The important thing to remember is that current always flows in loops and you have many loops from different subcircuits which share common copper paths in a net called a ground. The question is do you know which currents are combined and how this affects their subcircuits?
"That is a question which is bigger than this forum." And entirely off-topic: this forum is for discussing Keil Software tools - not the details of circuit design! http://www.keil.com/forum/ I suggest you go to the support sites of the major ADC manufacturers - eg, Analog Devices, National Semiconductor - and check out the design materials there...