基于MAX3946的10Gbps低功耗激光二极管驱动方案

Maxim 公司的MAX3946是+3.3V多速率低功耗激光二极管驱动器，数据速率高11.3Gbps，支持SFF-8431 SFP+ MSA 和and SFF-8472，3.3V时的功耗为225mW，可编程调制电流从10mA到100mA，可编程偏压电流从5mA到80mA，以及可编程输入均衡和输出去加重。

MAX3946应用在4x/8x FC SFP+ 光收发器，10GFC SFP+光收发器，10GBASE-LR SFP+光收发器，10GBASE-LRM SFP+光收发器和OC192-SR XFP/SFP+收发器。本文介绍MAX3946主要特性和方框图，AC测试电路图，眼安全电路图以及10GBASE-LRM应用电路图和10GBASE-LR应用电路图。

The MAX3946 is a +3.3V, mulTIrate, low-power laser diode driver designed for Ethernet and Fibre Channel transmission systems at data rates up to 11.3Gbps. This device is opTImized to drive a differenTIal transmit­ter opTIcal subassembly (TOSA) with a 25I flex circuit. The unique design of the output stage enables use of unmatched TOSAs, greatly reducing headroom limita­tions and lowering power consumption.

The device receives differential CML-compatible signals with on-chip line termination. It can deliver laser modula­tion current of up to 80mA, at an edge speed of 20ps (20% to 80%), into a 5I to 25I external differential load. The device is designed to have a symmetrical output stage with on-chip back terminations integrated into its outputs. A high-bandwidth, fully differential signal path is implemented to minimize deterministic jitter. An equalization block can be activated to compensate for the SFP+ connector. The integrated bias circuit provides programmable laser bias current up to 80mA. Both the laser bias generator and the laser modulator can be dis­abled from a single pin, DISABLE.

A 3-wire digital interface reduces the pin count and permits adjustment of input equalization, pulse-width adjustment, Tx polarity, Tx deemphasis, modulation cur­rent, and bias current without the need for external com­ponents. The MAX3946 is available in a 4mm x 4mm, 24-pin TQFN package.

MAX3946主要特性：

225mW Power Dissipation Enables < 1W SFP+ Modules

Up to 100mW Power Consumption Reduction by Enabling the Use of Unmatched FP/DFB TOSAs

Supports SFF-8431 SFP+ MSA and SFF-8472 Digital Diagnostic

225mW Power Dissipation at 3.3V (IMOD = 40mA, IBIAS = 60mA Assuming 25I TOSA)

Single +3.3V Power Supply

Up to 11.3Gbps (NRZ) Operation

Programmable Modulation Current from 10mA to 100mA (5I Load)

Programmable Bias Current from 5mA to 80mA

Programmable Input Equalization

Programmable Output Deemphasis

25I Output Back Termination at TOUT+ and TOUT-

DJ Performance 7psP-P with Mismatched Differential Load (5I)

DJ Performance 5psP-P with Mismatched Differential Load (25I)

DJ Performance 5psP-P with 50I Differential Load

Programmable Pulse Width

Edge Transition Times of 20ps

Bias Current Monitor

Integrated Eye Safety Features

3-Wire Digital Interface

-40℃ to +95℃ Operation

MAX3946应用：

4x/8x FC SFP+ Optical Transceivers

10GFC SFP+ Optical Transceivers

10GBASE-LR SFP+ Optical Transceivers

10GBASE-LRM SFP+ Optical Transceivers
 
OC192-SR XFP/SFP+ Transceivers

图1。MAX3946功能方框图

图2。MAX3946 AC测试电路图

图3。MAX3946眼安全电路图

图4。MAX3946 10GBASE-LRM应用电路图

图5。MAX3946 10GBASE-LR应用电路图