A signal encoder and a signal decoder involves the signal encoder for receiving a data signal and a clock signal, including a first code output terminal and a second code output terminal. When the data signal is logic one, the signal encoder outputs a modulated signal through the first code output terminal, and outputs a fixed level signal through the second code output terminal. When the data signal is logic zero, the signal encoder outputs the fixed level signal through the first code output terminal, and outputs the modulated signal through the second code output terminal. The signal decoder converts the modulated signal and the fixed level signal output from the signal encoder into the data signal and the clock signal.
