▁presents ▁the ▁C M OS ▁designer ▁with ▁a ▁challenge , ▁because ▁in ▁C M OS ▁the ▁volt ages ▁go ▁only ▁to ▁ground ▁and ▁the ▁supply ▁voltage , ▁the ▁source , ▁gate , ▁and ▁d rain ▁terminal s ▁of ▁the ▁F ET s ▁have ▁only ▁the ▁supply ▁voltage ▁or ▁zero ▁voltage ▁across ▁them . ▁ ▁The ▁M OS F ET ▁formula : ▁ ▁says ▁that ▁the ▁current ▁ ▁supplied ▁by ▁the ▁F ET ▁is ▁proportional ▁to ▁the ▁gate - source ▁voltage ▁reduced ▁by ▁a ▁threshold ▁voltage ▁, ▁which ▁depends ▁on ▁the ▁geomet rical ▁shape ▁of ▁the ▁F ET ' s ▁channel ▁and ▁gate ▁and ▁their ▁physical ▁properties , ▁especially ▁capac it ance . ▁To ▁reduce ▁ ▁( necess ary ▁to ▁reduce ▁supply ▁voltage ▁and ▁increase ▁current ) ▁one ▁must ▁increase ▁capac it ance . ▁However , ▁the ▁load ▁being ▁driven ▁is ▁another ▁F ET ▁gate , ▁so ▁the ▁current ▁it ▁requires ▁is ▁proportional ▁to ▁capac it ance , ▁which ▁thus ▁requires ▁the ▁designer ▁to ▁keep ▁capac it ance ▁low . ▁▁ ▁The ▁tr end ▁towards ▁lower ▁supply ▁voltage ▁therefore ▁works ▁against ▁the ▁goal ▁of ▁high ▁clock ▁speed . ▁Only ▁improvements ▁in ▁phot ol ith ography ▁and ▁reduction ▁in ▁threshold ▁voltage ▁allow ▁both ▁to ▁improve ▁at ▁once . ▁On ▁another ▁note , ▁the ▁formula ▁shown ▁above ▁is ▁for ▁long ▁channel ▁M OS F ET s . ▁With ▁the ▁area ▁of ▁the ▁M OS F ET s ▁hal ving ▁every ▁ 1 8 - 2 4 ▁months ▁( Mo ore ' s ▁law ) ▁the ▁distance