Perhaps you are able to design it in 1.8V and operated the MOSFETs in saturation, should the design schematic be altered or changed if it is to be operated at subthreshold for example at 0.5V supply?

 

Schematics?

Sub-threshold? of what?

 

schematic of the circuit in 1.8V supply

 

I am confused about the nature of the original question. Are you asking if it is possible to take a design that uses a VCC of 1.8 Volts and change it to a design that runs with a VCC of 0.5 Volts. I think there is a lower limit on VCC somewhere below 1.8Volts, maybe in the 0.9 Volt range, but I think 0.5 Volts is out of the question. Using behavioral models in a simulator you could probably do it, but that won't be too useful in the real world.

EDIT: If it did exist, this is what it might look like: