Digitalcircuitsoperatinginthesub-thresholdregimeconsumetheleastenergy.Thestrictenergyconstraintsaredesiredintheapplicationswhichworkatthelowestpossiblesupplyvoltage.Ontheotherhand,theconventionaldesignflowutilizesthetechnologylibraryprovidedbythefoundrywithafixedvoltageboundary,whichcausesproblemswhenthesupplyscalesdowntothesub-thresholdregime.Inthispaper,wepresentadesignmethodologytocharacterizetheexistingcelllibrarywithLibertyNCXtofacilitatethestandarddesignflow.Itisdemonstratedin0.13mcomplementarymetal-oxide-semiconductor(CMOS)technologywiththesupplyvoltageof300mV.