基于MAX3946的10Gbps低功耗激光二極管驅動方案

Maxim 公司的MAX3946是+3.3V多速率低功耗激光二極管驅動器，數據速率高11.3Gbps，支持SFF-8431 SFP+ MSA 和and SFF-8472，3.3V時的功耗為225mW，可編程調制電流從10mA到100mA，可編程偏壓電流從5mA到80mA，以及可編程輸入均衡和輸出去加重。

MAX3946應用在4x/8x FC SFP+ 光收發器，10GFC SFP+光收發器，10GBASE-LR SFP+光收發器，10GBASE-LRM SFP+光收發器和OC192-SR XFP/SFP+收發器。本文介紹MAX3946主要特性和方框圖，AC測試電路圖，眼安全電路圖以及10GBASE-LRM應用電路圖和10GBASE-LR應用電路圖。

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應用：

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

圖1。MAX3946功能方框圖

圖2。MAX3946 AC測試電路圖

圖3。MAX3946眼安全電路圖

圖4。MAX3946 10GBASE-LRM應用電路圖

圖5。MAX3946 10GBASE-LR應用電路圖