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Santel chipset achieves optical compensation

Posted: 11 Sep 2002 ?? ?Print Version ?Bookmark and Share

Keywords:santel networks? s44501? s44003? phy chipset? sonet chipset?

Startup Santel Networks Inc. is pushing the chip level integration of optical compensation a notch higher. The company will show the first fruits of research in chromatic dispersion and polarization-mode dispersion on September 15 at the National Fiber Optics Engineers Conference in Dallas, Texas.

Santel Network's S44501/S44003 10Gb chipset integrates both those compensation techniques in PHY-layer devices that also include clock and data recovery.

The development is likely to ignite competition with optical-only compensation companies - which use largely passive techniques to handle both types of dispersion - and with DSP specialist Big Bear Networks Inc., which recently inked a deal with IBM Microelectronics to move to silicon germanium for compensator designs.

At present, Santel is the only player offering components on an individual chipset basis. Big Bear sells transponder subsystems, and other PHY-layer SONET chipset players are only in the early stages of offering compensation devices.

Pulse distortion

Chromatic dispersion and polarization-mode dispersion (PMD) can cause pulse distortion of an optical signal, a problem that gets worse with both speed and distance. While dispersion problems become particularly relevant at 40Gbps, Santel executives recognized that a solution for 10Gbps is important both for OEMs with node-specific bottleneck problems and for the compensation vendor as well.

Since 40Gb networks may not proliferate widely for several quarters, Santel had to develop a chipset to bring in revenue in the short term.

Key to realizing the chipset was proprietary work on adaptive equalization. The SS44501 SiGe signal conditioner monitors the incoming optical bit stream and creates a digital filter on the receive side.

The CleanSignal adaptive-equalization technology filters out effects of signal distortion, and the companion CMOS SS4403 digital controller works with the conditioner to create a DEMUX output of 16-bit words, synchronized to the recovered clock signal output. The chipset can be used with client-side devices such as MUX or forward-error correction devices.

The chipset accepts input of 9.95Gbps to 12.5Gbps from a TIA or photodiode, a range that allows its use in networks utilizing FEC or digital-wrapper overheads. The chipset can accept a 20mV differential input voltage swing, and uses a PECL-level reference clock input. Clock outputs are at LVDS levels.

The instantaneous PMD compensation is 65ps, while a secondary PMD compensation is rated at 2ns. Chromatic-dispersion compensation is 1.7ns/nm. The 3.3V chipset meets jitter tolerance requirements of GR-1377-CORE.

The SS44501 comes in a 196-pin BGA and the SS44003 in a 256-pin BGA. The units are sold under $500 per two-chipset and general samples will be available in November.

- Loring Wirbel

EE Times

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