An off chip driver circuit includes a pull-up circuit and a pull-down circuit. The pull-up circuit includes several first transistors and a first resistance circuit coupled between the first transistors and a input/output pad. The first transistors generate a first voltage to the first resistance circuit. The first resistance circuit transmits, in response to a first control signal, the first voltage to the input/output pad and to have a variable resistance according to the first control signal. The pull-down circuit includes several second transistors and a second resistance circuit coupled between the second transistors and the input/output pad. The second transistors generate a second voltage to the second resistance circuit. The second resistance circuit transmits, in response to a second control signal, the second voltage to the input/output pad and to have a variable resistance according to the second control signal.