i know that PMOS is used for getting strong 1 and NMOS for getting strong 0. Also, if w will use NMOS as pull up it will only b able to pull the output upto vdd-vt and in case of PMOS in pull down it will be vss+vt. so can someone please explain this voltage changes at device level with respect to the working of MOSFET or please suggest any suitable links or documents to read.