Duobinary is a pseudobinary coding
that works with two different hi-levels, one positive and one negative, and with a zero level. It thus belongs to the three-level or ternary coding methods.level
. Which level state is represented depends on the number of logic zero states after the last 1 state. If there is an even number of zeros since the last 1-level, the positive 1-level is used; if there is an odd number of zeros, the logic 1 is represented by the negative 1-level. Duobinary signals require less bandwidth than NRZ encoding. In addition, some errors can be detected without additional parity bits.