Quote:The main design specifications whilst designing the o/p stage are a) output swing, b) power dissipation (or efficiency), c) linearity (or THD). Please let me know are there anything else I need to consider.
Yes, The kind of load it needs to drive & how much of it ?
Quote:2. My 2stage diff-amp works with 1.8 V - 0 V supply rail. So, the output stage also need to be designed among those. Which topology should I go for?
Depends on the above mentioned factors + the answer.
Quote:3. After inserting the third stage is it required to again compensate the whole circuit? And any other design metric dependent upon both the driver stage and output stage needs to be considered?
Yes, Esp. if the output driver's a gain stage.
Quote:4. Any simple design guideline is very much appreciated.
Again there are numerous topologies ranging from a simple common drain config to complex drivers like class AB & others. Choose the one which fits your specs. There's plenty of material on output stages.
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Mayank