Electronic Design

Serializer/Deserializer Creates Low-Cost, Short 10-Gbit/s Optical Links

Designers of optical transmission equipment estimate that 80% of SONET OC-192 10-Gbit/s (9.952-Gbit/s actual) links are 100 meters or less. Typically, these links are located in a central office to interconnect switches, routers, and dense wave-division multiplexing (DWDM) equipment. A single 10-Gbit/s link could be used instead, but it is a very expensive option.

Multiple slower serial links present an alternative that's less expensive. These links permit designers to use lower-power and low-cost vertical-cavity surface-emitting lasers (VCSELs) and a multifiber ribbon cable. But they also need the transmitter/receiver interface circuitry to work with the SONET framers. A high-speed ASIC can be made to do the job, of course. Or, designers can employ the Vitesse VSC7166.

The VSC7166 is a 16-bit parallel-input serializer/deserializer with 12 serial channels out. The chip's transmitter portion accepts 16-bit low-voltage differential-signaling (LVDS) parallel inputs at 622 MHz from an OC-192 framer and converts the data into 12 1.244-Gbit/s serial LVDS outputs. During the conversion, the data undergoes 8B/10B encoding.

Ten outputs carry the data. The eleventh channel is derived by XORing the bits from the other 10 channels. Should one channel fail, the resulting bit stream permits data recovery. A 16-bit cyclical redundancy check (CRC) used for error detection and correction (EDC) generates the 12th channel. Total throughput is 12.44 Gbits/s, with a data rate of 10 Gbits/s.

The receiver section translates 12 1.244-Gbit/s LVDS serial inputs into parallel 16-bit LVDS outputs at 622 MHz. The translation process includes the 8B/10B decoding as well as error detection and correction. And, an internal PLL locked to the data sampled from channels 6 or 7 generates the receive clock.

The VSC7166 complies with Optical Internetworking Forum (OIF) 99.120 standards. It's compatible with Vitesse's VSC9116 SONET framer chip as well. With 1.8- and 2.5-V power supplies, the chip dissipates a maximum of 5 W. Available in a 256-pin, 27-mm BGA package, this serializer/deserializer costs $70 each in 10,000-unit quantities. Samples are now available.

Vitesse Semiconductor Corp., 741 Calle Plano, Camarillo, CA 93012; (805) 388-3700; fax (805) 987-5896; Internet: www.vitesse.com.

See associated figure.

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