Analysis of pre-equalized multilevel partial response schemes for high-speed electrical interconnects

In this paper we complement the overview of the basic baseband modulation in high-speed electrical interconnects by a detailed analysis of the equalization. We present a mathematical framework for the equalization and elaborate on different equalization aspects. We discuss the interplay between the choice of modulation and the equalization on the one hand and the properties of electrical interconnect on the other. We consider a reference electrical interconnect and show that appropriate selection of modulation target according to the channel shape can significantly improve the performance at reduced equalization complexity. For the assumed reference channel, three modulation formats are analyzed, namely the pulse amplitude modulation (PAM), duobinary and one polybinary scheme that are combined with 2-PAM. We further analyze multilevel mapping (L > 2)-PAM combined with partial response signaling for the same channel and show that in selecting higher mapping order the number of signal levels can explode with the line coding which will degrade the error performance. Exploiting the correlation of the partial response signals in the detection via the sequence detection, can significantly improve the performance. Closed-form performance analysis by means of different error ratio approximations derived in this paper is considered and further compared to simulations.