Electronic Design
Digital Laser Diode Driver Interface Enhances SFP+ Optical Module Controller

Digital Laser Diode Driver Interface Enhances SFP+ Optical Module Controller

The small-form-factor pluggable (SFP) module is probably the most popular optical transceiver format for both data communications and telecommunications applications. These transceivers run at data speeds to 10 Gbits/s, so they’re a challenge to implement. Now, Maxim Integrated Products is making life easier for designers of SFP modules by introducing the DS1878, a small-form-factor pluggable plus (SFP+) controller with a digital laser diode driver (LDD) interface. State-machine-based, the DS1878 eliminates the need for software development. It enables efficient implementation of the SFF-8472 specification and greatly reduces time-to-market.

The SFF-8472 standard defines digital monitoring and diagnostics functions. The DS1878 implements these controls and monitors all functions for small-form-factor (SFF), SFP, and SFP+ optical modules and fully supports the SFF-8472 standard (see the figure). It can be combined with a MAX3798 or MAX3799 SFP+ laser driver/limiting amplifier to provide an automatic power control (APC) loop, modulation current control, and eye safety functionality—the core feature set of SFP and SFP+ optical modules. The DS1878 also works with the MAX3945 limiting amplifier or the MAX3946 LDD to support 10-GHz applications featuring distributed feedback (DFB) or electro-absorption-modulated (EML) lasers.

Laser modulation is controlled with a dedicated temperature-driven lookup table (LUT). Two additional 9-bit delta-sigma digital-to-analog converter (DAC) outputs with 36-entry LUTs are provided. The DS1878 monitors six analog channels: temperature, VCC, and MON1 to MON4, which can be used to monitor laser current, optical output power, and optical input power.

The DS1878 is specified from –40°C to 95°C. It uses 0.35-μm technology to enable the high level of integration required for SFF-8472 implementation in a small 5- by 5-mm, 28-pin thin quad flat no leads (TQFN) package with exposed pad. Pricing begins at $1.33 in 1000-unit quantities.

Maxim Integrated Products

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