Other materials such as silicon germanium or aluminum gallium arsenide will have the speed to handle OC-768 (40-Gbit/s) Sonet communications, but InP has a number of advantages for Vitesse's goals, said Ira Deyhimy, vice president of engineering.

Specifically, Vitesse would like to use one process for all parts up to the packet-processing stage, which will make it easier to integrate those devices later. Components such as laser drivers can only be produced with InP when the 40-Gbit/s threshold is reached.

In addition, indium phosphide has a transistor cutoff frequency of 160 GHz, compared with 90 GHz for SiGe and even less for AlGaAs — critical because the cutoff frequency should ideally be three times the operating frequency, Deyhimy said. InP also has a lower threshold voltage for turning on transistors, making 3.3-volt systems easier to design, he said.

Overall for OC-768 systems, Vitesse expects to use InP to produce transimpedence amplifiers, postamplifiers, laser drivers, multiplexer/demultiplexer parts, clock multiplier units and clock-and-data recovery circuits.

The LAN switch fabric, along with functions such as encoding and decoding for forward error correction, will remain in CMOS. The switch fabric, specifically, has room to spare, as Vitesse is preparing to announce CMOS-based switch fabrics with speeds of up to 4 Tbits/s, debuting in at least three separate generations of product.

Experience counts

While InP has yet to be used for commercial products, Deyhimy pointed to Vitesse's track record at perfecting increasingly advanced GaAs processes.

"We have a substantial process development group, and H-GaAs V Vitesse's most advanced GaAs process is going into production right now," he said. "Those same people will work on InP."

Kenneth Jones, vice president and general manager of advanced transmission products for Vitesse, said that the urgency of getting 40-Gbit parts out is great enough to warrant Vitesse turning to a foundry for the next year or so, as it brings up its own 1-micron InP process in Camarillo, Calif. Jones refused to name the foundry, though Agilent Technologies, CyOptics, and several defense contractors have worked with InP in the past.

Test modules are being inserted into the foundry partner's InP wafers now. The first InP products for OC-768 should be ready for sampling by the end of the year, but the ramp to production volumes won't even start until 2002, Deyhimy said.

Meanwhile, Vitesse's fabrication facility in Colorado Springs, Colo. will be dedicated to new products using the 0.25-micron H-GaAs V process, with four aluminum layers and 16 mask layers. That process will move from 3.3 Vto 2.5 V and 1.8 V.

Newer generations of OC-192 1:16 and 1:4 mux/demuxers will move to this new 3.3-V version of the process. Because InP is still a III-V process, Vitesse will refer to it internally as "H-GaAs VI," even though all previous H-GaAs generations are MESFET-based, and the InP process is a heterojunction bipolar transistor process.

The tricky realm will be analog and physical-layer devices for OC-192. Vitesse continues to design a range of parts in both H-GaAs V and silicon germanium, and will offer SiGe devices on a foundry basis if it makes sense to do so. More than anything else, however, Vitesse wants to be known as process-neutral, Jones said. He pointed out that 60 percent of the company's design engineers now design in CMOS, used in OC-48 and OC-192 devices, as well as in Gigabit Ethernet and Fibre Channel components.

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