Hi, ASHUTOSH RANE
Two examples of biasing nmos are depicted on the picture below:
The first way (left current source on the picture ) is the most simple way if you have enough voltage headroom. And the second way (right current source on the picture) lets you increase the dynamic output voltage range at the cost of drop in output resistance.The width of transistor N11 is 9 times less than that of other transistors in this example. You can vary this parameter and see how the picture of output resistance vs. output voltage changes and choose appropriate value.
Small signal output resistances are on the figure below:
Regards, pavel.