A signal transmitter includes a plurality of driver slices. Each of the driver slices includes a driving circuit, a plurality of first transistors, and a plurality of second transistors. The driving circuit receives an input signal and outputting an output signal. The first transistors provide a first impedance according to signals on gate terminals of the first transistors. The second transistors provide a second impedance according to signals on gate terminals of the second transistors. Each of the gate terminals of the first transistors and the second transistors is selectively coupled to a bias voltage which controls the corresponding first transistor or second transistor to operate in a triode region, or coupled to a predetermined voltage which controls the corresponding first transistor or second transistor to behave as a switch.