Laser driver chipset targets SFP+ transceivers

SEPTEMBER 11, 2008 -- The VSC7985 and VSC7986 are optimized for use in SFP+ optical transceivers, but also can be used in XFP and Xenpak modules and dense parallel-optic line cards.

SEPTEMBER 11, 2008 -- Vitesse Semiconductor Corp. (search for Vitesse) earlier this week introduced the VSC7985 and VSC7986, the latest members of Vitesse's 10-Gbit/sec laser driver family. The VSC7985 and VSC7986 are optimized for use in SFP+ optical transceivers, but also can be used in XFP and Xenpak modules and dense parallel-optic line cards.

As a chipset, the new direct-modulated laser diode (DML) drivers are designed to meet the stringent power requirements of 8-Gbit/sec Fibre Channel as well as 10-Gigabit Ethernet and SONET/SDH networks. As a single chip, the VSC7985 can be used as a VCSEL driver for short-reach optical applications.

According to Vitesse, module OEMs and system integrators have struggled with meeting the 1-W power limit of SFP+ transceivers in long-range fiber applications, especially in laser end-of-life (EOL) conditions where bias and modulation currents can increase dramatically. The VSC7985 and VSC7986 are designed to offer a significant breakthrough in power by saving up to 40% compared to traditional DML drivers, due in part to a unique architecture and low-power design. The chipset also streamlines a common footprint PCB design to serve both long- and short-reach optical module applications, thus further reducing the bill-of-material (BOM) cost and engineering characterization time, the company says.

The VSC7985, a pre-driver that can be used in standalone fashion for short-wavelength 8G and 10G SFP+ module designs, is designed to offer signal integrity features needed in SFP+ applications such as programmable input equalization and output pre-emphasis and de-emphasis. The programmability enables optimization of optical eye margins across several inches of printed circuit board and various VCSEL lasers. The VSC7985 also features a two-wire serial interface or SPI interface to simplify integration in the SFP+ transceiver. Vitesse says the laser driver offers optimal jitter and data eye performance as well.

The companion VSC7986 amplifier is used in TOSA applications and offers DC single-ended coupling direct to a DML laser. The linear gain amplifier is compact in die size to allow for easy integration in a TO-style package. The DML modulation and bias current can be controlled by the VSC7985, thus further reducing power dissipation, eliminating bulky external components, and reducing overall board footprint, according to Vitesse.

The VSC7985 and VSC7986 are sampling now. Electrical and optical evaluation boards are also available.

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