a mixed - voltage i / o buffer comprises an input circuit , an output circuit , an i / o pad , a pre - driver circuit coupled to the output circuit , two added coupled n - type transistors , and a dynamical gate - controlled circuit coupled to each gate of the two n - type transistors and the pre - driver circuit ; one of the n - type transistors is coupled to the input circuit and the output circuit ; the other n - type transistor and the dynamic gate - controlled circuit are together coupled to the i / o pad . thereby , a mixed - voltage i / o buffer which receives 2 × vdd - tolerant input signals and overcomes the hot - carrier degradation is realized .