Inclusive Modeling and Digital Compensation for Coupling Impairments of High-Speed Coupled Electrical Microstrip Traces in 100G OOK and PAM4 Data Center Connections

Abstract

Pluggable transceiver modules become the preferable form factor in data centers connectivity due to the lower power consumption and smaller size, which allows high port density. In such small form factors, the optical components may be packaged separately from the electronic blocks. This introduces a new challenge for transmission of ultra-broadband signal over high-speed coupled printed analog traces, as the coupling impairments are enhanced dramatically. Here, an extended model of coupling impairments of coupled microstrip traces in optical fiber communication systems is proposed. This model consists of an accurate formulation of the frequency dependency, which is shown to be critical in the transmission of ultra-broadband signals. In addition, a comparison is presented to standard practice coupling models that are currently being used for crosstalk cancellation techniques in sub-10G systems or very short traces. Based on the inclusive coupling model, novel coupling compensation techniques are proposed and are compared with the classical ones. Comprehensive analysis, which is verified by Monte-Carlo simulation, reveals that the newly introduces coupling compensation technique significantly outperforms the existing crosstalk compensation solutions, for 25G transmission and beyond, thus, longer coupled traces are supported. The new approach is based on symbol-spaced sampling and reduced-complexity digital signal processing. It is shown in the case of 100G PAM4 transmission, based on commercially available 25G components, the newly proposed compensation technique supports long microstrip traces of more than 15 cm, while maintaining 10 -3 pre-forward error correction (pre-FEC) bit error rate (BER).