3.3 A 25Gb/s multistandard serial link transceiver for 50dB-loss copper cable in 28nm CMOS

Abstract

The amount of data traffic is increasing year by year as the number of data-rich services like cloud services and streaming services are increasing. The number of switch modules between servers should decrease to lower latency, and several servers in each rack should be connected to one switch module with cables in a data centre. Using copper cables to connect racks is attractive in terms of cost minimization. Thin cables, for example 34 AWG copper cables, make maintenance easy. The cable length should be 5-7m to connect between racks, and 34 AWG 7m cable has 48dB loss, including board trace loss, package loss and so on. So far transceivers over 25Gb/s, equalizing 35-40dB channel loss have been proposed [1-4], with which low-loss cables like 26 AWG have been required. We target a 25Gb/s transceiver equalizing over 50dB channel loss, and adopt a sub-mV dynamic DC offset cancelation and a decision-feedback equalizer (DFE) with a bias-controlled tap slicer. Both improve on the minimum input sensitivity and enable data transmission through a channel with over 50dB loss.