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

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

• Irfan N. Ali
• Michael C. Clowers
• David S. Fink
• Sean K. Garrison
• Jeff A. Magee

March 3, 2008
Georgia Institute of Technology School of
Electrical Computer Engineering
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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

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Technical Objectives

• 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)

Driver Board
Interface Board
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Technical Specifications
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Design Approach

• Three parallel approaches
• Modify MAXIM Inc. evaluation board
• Populate existing Analog Devices (AD) driver
  board
• Design driver board for TI chip

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Analog Devices Board

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

Digital Inputs
Output to VCSEL
Laser Driver
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Maxim Inc. Evaluation Board

• Evaluation board designed for laser diode
• Interface board designed to deliver limited
  modulation and bias currents to VCSEL

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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 Input
Digital Outputs
Digital Inputs
Power Supply
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VCSEL Interface Board Schematic

• Interfaces the TI and MAXIM Inc. boards with the
  VCSEL
• Includes resistance networks to limit current to
  VCSEL

Analog VCSEL Output
Analog VCSEL Output
Digital Inputs
Digital Input
MAXIM Interface
TI Interface
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System Configuration
Note SMA connections use coax cables
Optical cables use LC connectors
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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

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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

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Budget Cost Analysis

• 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. Ralphs lab

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

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Projected Schedule

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

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Current Status

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

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Questions/Comments

• Thank You