A transmission device includes a first encoder, a plurality of current sources, a switch module, a second encoder, and a plurality of current enhanced circuits. The first encoder converts an input signal to a first control signal. The switch module is coupled between the plurality of current sources and a plurality of signal lines for controlling the connection of the current sources and the signal lines according to the first control signal to generate a current signal. The second encoder generates a second control signal according to the first control signal or the input signal. The plurality of current enhanced circuits is coupled to the plurality of current sources respectively. The plurality of current enhanced circuits provides an extra current in a predetermined duration to enhance the current signal.