Comparison Between NRZ, PAM-3, PAM-4 and Duobinary Modulation in High-Speed Serial Interfaces

We employ a modeling approach based on the probabilistic construction of the eye diagram to benchmark NRZ, PAM-3, PAM-4 and Duobinary for high-speed serial interfaces in the $>10 ~\text{Gb} / \mathrm{s}$ range. A realistic model for the channel attenuation is used and equalization is applied to the system. The different modulation schemes are compared at different data rates and channel attenuation for the same transmitted voltage swing, identifying the most efficient modulation in the various situations. Duobinary is implemented here by setting the transmitter equalizer so that a single bit results in a pulse response of the channel-plus-equalizer system extending over two bit periods.