Electronic Design

Twisted Pair Defies The Laws Of Physics With 10 Gbits/s

The first time someone told me it was possible to transmit baseband serial digital signals at 10 Gbits/s over copper cable, I thought it was some kind of April Fool's gag. But it really is happening. It just isn't easy.

Several companies have been working on a cheap way to implement 10 Gigabit Ethernet (10GE) over the installed base of CAT5e/6 twisted pair. 10GE has been around a while, but its adoption has been limited because of the higher cost of the fiber-optic cable alternatives. Thanks to KeyEye Communications, a copper solution is now available. Its EchoWave KX1001 and KX1003 transceiver chips deliver a solid 10 Gbits/s over standard four-pair CAT5e/6 cable.

The main application is server and switch connectivity in data centers. With high-speed interconnects, data centers can deliver higher throughput, quicker response times, and faster transaction rates. As data centers migrate to server clusters, grid computing, and storage systems, higher data rates are essential to maintaining performance.

All of these devices are typically located close to one another in the data center. Statistics show that about 80% of these products are within 35 m of one another. So, a 10-Gbit/s solution with a reach of at least 35 m would cover just about most applications. For longer distances, one of the standardized fiber optic 10GE solutions could be used.

The IEEE also is developing a 10GE standard that will reach 100 m with CAT6/7 cable but require a special connector. Known as 802.3an, this standard should be ratified sometime next year. In the meantime, KeyEye's transceivers provide a very affordable solution for data center connectivity. They target network interface cards (NICs), Ethernet switches, stacking links, and optical multisource agreement (MSA) module replacement.

The KX1001 delivers 10-Gbit/s Ethernet with four transceivers over four pairs of CAT 5e/6 cable with standard RJ-45 connectors. The data is transmitted using PAM-4 multilevel coding at 3.125 Gbits/s on each pair, producing an aggregated data rate of 4 3.125 = 12.5 Gbits/s. This rate includes the 8B/10B FEC for a raw data rate of 10 Gbits/s. Full duplex operation is implemented at that rate. The transceiver has a standard Ethernet XAUI interface on one side and the twisted pair on the other. While some solutions use DSP, the KeyEye transceiver is an analog device. Analog circuits perform the necessary processing to correct signal impairments and provide signal restoration and cancellation functions, such as equalization and echo and crosstalk cancellation.

These circuits also consume considerably less than the 10 W or so usually associated with a DSP solution. The KX1001 has a total dissipation of less than 3.7 W, making it a viable replacement for XENPAK, X2, and XPAK optical MSA solutions at 20% lower cost. Each transceiver maintains a bit error rate (BER) of at least 10 to 12 and meets stringent class A and B electromagnetic interference requirements. Latency is less than 150 ns.

The KX1003 is a 4x InfiniBand transceiver. Despite its high cost and complexity, InifiniBand has survived mainly because a 10-Gbit/s technology over short distances is still necessary. The original InfiniBand solution used eight coax cables with a special connector to deliver 10 Gbits/s over 15 m. Using the same PAM-4 technology and continuous adaptive equalization, the 10-Gbit/s rate now can be obtained with the KX1003 in InfiniBand routers, switches, and host channel adapters.

The KX1001 and KX1003 come in a 14- by 14-mm, 256-pin FBGA package. A 19- by 19-mm, 324-pin LFBGA package also will be available. The KX1001 costs $60 in 5000-unit lots, while the KX1003 is $60 in 1000-unit lots. Reference designs, evaluation boards, and application notes are available.

KeyEye Communications Inc.

TAGS: Digital ICs
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