In Hspice manual, I see the different definition of AD.
At "Active Elements" section in Hspice manual, AD is "drain diffusion area."
At "MOSFET Output Templates" section, I see its definition is changed to "area of the drain diode."
user raptor1981 wrongly posted reply to report system:
hi, AD is the drain area of MOSFET . AD is not related with the diode area . This can be observed from the model file of AMS , here there are specific models for all elements . For further details please refer to the website ( search by ams )
AD, like the others said, is the Drain area (Channel Width * Drain Length). The area of drain diode is the area at the botton of the diffusion plus the area of the difusion sidewalls. The picture gives a better explanation.