VCSEL Driver And Limiting Amp IC Match 10GE, 8G Fibre Channel Apps

When designing multisource agreement (MSA) optical transceiver modules such as SFP and SFP+, you need a superior compact laser driver and a photo diode amplifier to provide the performance expected in 10-Gbit/s applications. Maxim Integrated Products’ MAX3798 gets the job done (see the figure). Expected uses include 1/2/4/8-Gbit/s Fibre Channel and 10G Ethernet (10GE) including 10GBaseSR, 10GBaseLR, and 10GBaseLRM. Speeds to 10.32 Gbits/s using NRZ are possible.

The receiver amplifier takes the signal from the PIN photo diode and transimpedance amplifier in differential form and limits it into a CML-level differential output. Typical receiver sensitivity is 3 mV p-p. The laser driver is designed for use with vertical-cavity surface-emitting lasers (VCSELs) operating at 1310 nm. The VCSEL driver provides for modulation and bias current adjustment.

The average optical power is controlled by an average power control (APC) loop implemented by a controller that interfaces to the VCSEL driver through a three-wire interface. The three-wire interface permits a wide range of advanced RX and TX modes and settings. On-chip digital-to-analog converters (DACs) allow the use of an external controller to program the functions desired.

The MAX3798 is available in a 32-pin, 5- by 5-mm thin quad flat no-lead (TQFN) package. Prices for the device start at $6.18 in quantities of 10,000 or more.

LOUIS E. FRENZEL