All i know about the nrd and nrs is that they designate the equivalent number of squares of the drain and source diffusions; these values multiply the sheet resistance RSH specified on the .MODEL control line for an accurate representation of the parasitic series drain and source resistance of each transistor.
I am using 0.35 um cmos technology. is there any specific formula to calculate this for a particular dimensions of mosfet? Can anyone help me out in this?