Implementing a 10 Gb/s VCSEL Driven Transmitter for Short Range Applications

Irfan N. AliMichael C. Clowers

David S. FinkSean K. Garrison

Jeff A. Magee

Georgia Institute of TechnologySchool of Electrical & Computer Engineering

March 3, 2008

Project Objectives & Parameters

Objective: Design and implement 10 Gb/s VCSEL transmitter for fiber optic Ethernet systems

Client: Telecom service providers, server management groups, etc.

Projected Unit Cost: Approx. $700

• Design and implement a 10 Gb/s optical link• Digital/electrical input• Signal processing via laser driver• Electrical-Optical Signal conversion via VCSEL• Analog/optical output • Fiber optic data transmission• Bit-error-ratio tester (BERT)

Technical Objectives

Laser Driver

VCSELFiber Optic Cable

Pattern Generat

orBERT

Driver Board Interface Board

Technical Specifications

Bit Rate 10 Gb/s Nominal Wavelength 850 nm Power Supply 3.3 V Output Fiber 50-um Multimode Output Connector LC Board Dimensions Variable Max Transmission Range 100 m

Design Approach

• Three parallel approaches:• Modify MAXIM Inc. evaluation board• Populate existing Analog Devices (AD)

driver board• Design driver board for TI chip

Laser Driver

VCSELDigitalInput

IMOD

IBIAS

Analog Devices Board

• Pre-designed board• Needs to be populated and tested• Has analog control of output currents

Laser Driver

Digital Inputs

Output to VCSEL

Maxim Inc. Evaluation Board

• Evaluation board designed for laser diode

• Interface board designed to deliver limited modulation and bias currents to VCSEL

Digital Inputs

Laser Driver

Tuning Potentiometers

Output to Interface Board

TI Driver Board Schematic

• Driver board designed using PCB Artist• Provides digital control of output currents• Works with an interface board to connect to VCSEL

MCU InputDigital InputsPower Supply

Digital Outputs

VCSEL Interface Board Schematic

• Interfaces the TI and MAXIM Inc. boards with the VCSEL

• Includes resistance networks to limit current to VCSEL

Digital Input

Digital Inputs

Analog VCSEL Output

Analog VCSEL Output

MAXIM Interfa

ce

TI Interfa

ce

System Configuration

Note: SMA connections use coax cables Optical cables use LC connectors

Demonstration Plan

• Test by using the transmitter with a pattern generator to a send 10 Gb/s signal to error detector connected to optical receiver

• Measure bit-error-ratio (BER) versus optical power at receiver and compare to acceptable value of BER at 10-10

• Capture optical eye diagram using a high-speed oscilloscope

Problems/Issues

• Transmission lines for interface board need to be designed for high speeds

• SMA pad size on AD board does not match the SMA connector specification

• VCSEL connection to AD board may be incompatible with available VCSELs

• TI driver chip has 0.5 mm spacing between pins which will be difficult to solder by hand

Budget & Cost Analysis

Unit Cost Analysis

Fringe Benefits (% of labor) 25%

Overhead (% total labor, parts, fringe) 50%

Marketing (% sales price) 25% Warranty (% sales price) 5%

Costs (per unit) Materials $220

Labor $20

Testing $20

Fringe Benefits (25% labor cost) $5 Overhead $133

Sales/Marketing $250

Warranty $50

Amortized Development Costs $2.28

Cost Subtotal $700

Devices Acquired MAXIM Inc. Eval Board $300 Circuit Components Free Driver Chips Free Predesigned PCB Free Total Costs $300 Non-Budget Spending TI MCUs $80 Future Spending Circuit Components TBA SMA Connectors TBA

Power Supplies TBA

PCB Boards $80

•TI MCUs were bought as general use for the Senior Design Lab and therefore will not come out of the budget•Pre-designed PCB board

provided free of charge from Dr. Ralph’s lab

•Costs are based on total unit sale of 15000 over 5 years

Projected Schedule

Major Events Before Spring Break:•Completing PCB design and fabrication•Populating pre-designed board•Testing at TSRB

Current Status

• MAXIM Inc. evaluation board acquired• AD board partially populated• TI and interface boards designed • PCB mounting design initialized

Questions/Comments

Thank You