Binary code is a two level of bit sequence of 1 and 0. On the other side, Duobinary (DB) is a threelevel code of 1, 0 and -1 levels. Using duobinary transmission instead of binary transmission, it can improve the system performance, bandwidth efficiency of output signal, average power of signal, noise and distortion ratio of output wave shapes. Duobinary encoding and decoding are used in a significant bandwidth reduction of MAC signals transmitted by high and medium power TV satellites and also

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... used in fiber optic communication system. This paperis based on the the observationof generation performance and transmission of duobinary coding and simulation of a single channel (1550-nm) 90-km OC-192 link. In duobinary transmission, the duobinary encoding can be implemented either with a combination of a delay-and-add operation or with a duobinary filter. Duobinary filter reduces bandwidth , wavelength, noise and distortion and improves the eye diagram of the output signals than the delay-and-add circuit in duobinary transmission of optical communication system. Also in this paper circuit design, simulation and fabrication of a duobinary encoder and decoder circuit for data communication system are presented.