Transceivers bring copper up to speed

Analogix Semiconductor has introduced a new family of physical-layer transceiver ICs that lets system designers replace fibre optics with less expensive copper media in system-to-system interconnects.

Analogix Semiconductor has introduced a new family of physical-layer transceiver ICs that lets system designers replace fibre optics with less expensive copper media in system-to-system interconnects, yet still achieve the high performance associated with fibre.

Analogix's new D-PHY xGC family of physical-layer transceiver (PHY) chips includes the first device to deliver 6.25Gbit/s raw serial performance per copper twisted pair.

With an aggregate capacity of 25Gbit/s full-duplex over a single InfiniBand copper cable at up to 30m, it offers twice the speed and distance of today's standard 10GBase-CX4 chips.

This D-PHY 5GC device is also the first high-speed transceiver to operate over unshielded twisted pair, providing a less costly alternative to InfiniBand cable at a time when a high-speed UTP-based standard could be up to two years away.

It offers designers major advantages in high- speed, short-distance interconnect scenarios, such as stackable switches or cross-rack clusters, where costly fibre was previously the only choice.

The D-PHY 5GC and a standards-based counterpart, the D-PHY 2.5GC, are already sampling to customers.

The D-PHY 2.5GC, designed for customers connecting heterogeneous multivendor systems over copper media, is fully compliant with the 10GBase-CX4 standard, offering 4 x 3.25Gbit/s performance.

However, it operates over distances of up to 40m - nearly triple the 15m specification of the standard.

A second generation of the D-PHY xGC devices, offering serial speed up to 12.5Gbit/s and aggregate capacity of 50Gbit/s over InfiniBand cable and 25Gbit/s over UTP, will be available in 2005.

Like the 5Gbit/s devices, the two upcoming 10Gbit/s D-PHY xGC devices will include both a standards-based version (the emerging IEEE 10GBase-T standard) and a proprietary version offering higher speed and media flexibility.

Ted Rado, Vice President of Marketing for Analogix, said: "Today's system designers are between a rock and a hard place: if they need performance of more than a gigabit, they must use expensive fibre-based interconnect devices and perform electrical-optical conversions on both sides of the link".

"But fibre is overkill in the many cases where distance requirements are well under 100 metres - applications with single-vendor stackable switches or server blades, for example, or racked clusters of add-drop multiplexers or optical cross-connects".

"Standards efforts, while critical to the industry, do little to help these 'virtual backplane' types of applications, characterised by distances of 20 metres or less between like systems", Rado said.

"The current 10GBase-CX4 standard is limited to 3.125Gbit/s serial performance and works only on InfiniBand cable".

"The new 10GBase-T standard will offer much higher speeds and will be UTP-specific - but, even when it is finalised in the next 18-24 months, won't work with the ubiquitous Category 5e cable".

"The D-PHY xGC family fills this gap with an all-electrical solution that combines high performance with the flexibility to work with the user's choice of copper media".

With D-PHY xGC devices, designers can significantly reduce the cost of line cards without overhauling or replacing those cards.

The devices can be integrated into existing Xenpak and Xpak/X2 modules, providing a direct, all-electrical replacement for fibre-based transceivers.

Sending high-speed signals over copper cable, particularly unshielded cable, poses special challenges: high levels of crosstalk, impedance discontinuities at the cable/connector interface, and electromagnetic interference (EMI) that occurs at high frequencies.

The D-PHY xGC family addresses these challenges through a combination of advanced technologies on both the receive and transmit sides.

Two- stage, active linear equalisation on the receiver, with low power and die-area requirements, provides an appropriate high-frequency signal boost without introducing new noise effects or aggravating existing ones.

The highly sensitive receiver can recover signals from Analogix's very low-jitter transmitter, which uses minimal pre-emphasis and a low output swing to increase crosstalk immunity and address other noise issues.

The D-PHY xGC family also meets FCC Part 15 Class A EMI specifications.

The D-PHY 5GC transceiver comes in both dual and quad versions.

The D-PHY 2x5GC, with two high-speed (2.0-6.25Gbit/s) serial links and eight low-speed (500Mbit/s-3.125Gbit/s) links, provides up to 12.5Gbit/s performance over InfiniBand or UTP cable (Category 5e/6/7).

The D-PHY 4x5GC, with four high-speed and eight low-speed links, provides up to 25Gbit/s performance over InfiniBand cable, and up to 12.5Gbit/s over UTP cable.

Distances range from 3 to 25m on UTP, and 15- 35m on InfiniBand, depending on dat rate and cable type.

Two multiplexing options, 2:1 and 4:1, are available to address a wide range of customer applications.

The D-PHY 2.5GC device, compatible with the IEEE802.3ak (10GBase-CX4) standard, provides up to 12.5Gbit/s full-duplex transmission over up to 40m of InfiniBand cable.

The quad transceiver device, with four high-speed and four low- speed links (1:1 multiplexing), serves as a 10GBase-CX4 repeater, converting XAUI signals to CX4 signals for improved transmission over extended cable distances.

D-PHY xGC devices offer a bit error rate of 10e-17, far exceeding the 10e-12 BER specified by both the 1 and upcoming 10Gbit/s IEEE standards.

They are therefore better suited for "virtual backplane" solutions, which typically have higher reliability requirements than longer-range system interconnects.

And, unlike corresponding 10GBase-CX4 devices, which mandate 24-gauge InfiniBand cable with restricted bend radius, the D-PHY xGC family lets users optimise cable management for in-rack connections by allowing the use of 28- or 30-gauge InfiniBand cable, as well as UTP Category 5e, 6 or 7 cable.

All D-PHY xGC devices incorporate comprehensive built-in self-test (BIST) functionality, including on-chip PRBS generators and error checkers as well as low- and high-speed loopback paths for independent testing of all chip elements.

Consuming less than 3W of power, the D-PHY 5GC and 2.5GC devices compare favourably to upcoming 10GBase-T standard products, expected to consume more than 7W.

They can thus be integrated into copper-based versions of common optical modules, such as XENPAK, X2 or XPAK.

The first two members of the D-PHY xGC serdes family are now sampling and will be available in production quantities in the fourth quarter of 2004.

High-volume pricing is $45 per device for the D-PHY 2x5GC dual transceiver (up to 12.5Gbit/s); $75 per device for the D-PHY 4x5GC quad transceiver (up to 25Gbit/s); and $19 for the IEEE802.3ak-compatible D- PHY 2.5GC quad transceiver (up to 12.5Gbit/s).

D-PHY xGC products are manufactured using an advanced 0.13-micron CMOS process and come in JEDEC-standard 260-pin HSBGA (heat slug ball grid array) packages.

Two additional D-PHY xGC family members will be announced in the second half of 2005.

The D-PHY 10GCE will offer 10GBase- T-compatible performance of up to 12.5Gbit/s over 70-100m of Category 6/7 UTP cable.

The D-PHY 10GC, aimed at very-high-performance, short-range applications, will offer twice the performance of the 10GBase-T standard on UTP cable, and up to four times the performance of 10GBase-CX4 on InfiniBand.

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