Thank you very much for your reply,
seems a bit hard to me....
do you mean: the design parameters that effecting the min Vdd for a op amp are Vth?
but need to check with the corner situation?
other wise, if the Vdd is lower a bit more ( from satisfy all transistor to above Vth), then , at the design step, need to design transistors to working at subthreshold, right?
do I get what your mean ?
So, basicly, at the beginning of design, and I was gave a specification of a min Vdd,
then I just need to do all calculation on this min Vdd as operating point, right?
is it always have some way to fullfill the required min Vdd?
Or, normally , on the other hand, ---- do design first, fullfill other spec ( gain , BW, SR...) and then sweep the Vdd to see how min the Vdd could be?
Than you !!