A driver circuit for receiving input data and generating an output signal to a termination element is provided, wherein the input data has a first bit and second bit, and the driver circuit includes: a pair of differential output terminals for outputting the output signal, wherein the pair of differential output terminals has a first output terminal and a second output terminal; at least one current mode drive unit, coupled to the pair of differential output terminals, for outputting a current from one of the first output terminal and the second output terminal, and receiving the current from the other of the first output terminal and the second output terminal according to the first bit; and at least one voltage mode drive unit, coupled to the pair of differential output terminals, for providing voltages to the first output terminal and the second output terminal according to the second bit. The driver circuit can serve as a PAM-4 driver or an NRZ driver to support PAM-4 and NRZ codes.