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Analog Angle Article

Analog drivers/receivers improve SNR, reach of copper datacenter links

Pumping gigabit/sec data through the cables that link servers in datacenters without excessive loss or distortion requires thick-gauge copper, even as big as 24 AWG. Not only is the raw cost of copper a major expense, but routing these cables is a challenge due to their thickness. To overcome this problem, Quellan, Inc. in conjunction with cable provider W.L. Gore & Associates, has developed the QLx4600 Quad Lane Extender/Equalizer, an all-analog IC to extend the reach or reduce the copper needed, for interconnects from 2.5 to 6.25 Gbps.

The IC and cable assembly, which uses differential CML inputs and outputs, is transparent to the existing server I/O, provides both improved SNR as well as equalization, both of which contribute to data-recovery performance. As a result, users can get the same performance with 30 AWG cables as with 24 AWG, but with a significant reduction in copper, bend radius, and overall cable-routing problems. The IC is embedded in the cable connector, and automatically adjusts its channel parameters to reduce noise and channel loss. Unlike a mixed-signal approach which uses high-speed digitization and signal processing, the all-analog approach uses just 40 mA per channel when enabled, and imposes just 300 picoseconds of latency.

Each QLx4600 supports four channels (lanes) which can be enabled individually, and is priced at around $7.—Bill Schweber

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