Equalization and near-end crosstalk (NEXT) noise cancellation for 20-Gb/s 4-PAM backplane serial I/O interconnections

Abstract

Limitations in current backplane environments impede high-speed data transmission above 5 Gb/s. In this paper, a system architecture to extend the transmission capacities of legacy backplanes is proposed. The incentives for using a four-level pulse amplitude modulation (4-PAM) scheme are also presented. The architecture is built from feed-forward equalizer and tunable filter elements for near-end crosstalk noise cancellation. Each of the circuits is implemented in a standard 0.18-mum-CMOS process. The building blocks of the architecture, which include an LC ladder, a modified Gilbert-cell multiplier with improved headroom, and a tunable active high-pass filter are described in detail. Results of the architecture are shown demonstrating 20-Gb/s 4-PAM signal transmission.