Capstone Design Gigabit Ethernet Final Report Group 7 Shilo Ayalon gte351s Jed Eaton gte169h Dhairya Mehta gte764s Pranjal Shah gte711m Courtenay Smith gte274i Final Report ECE 4006 C Spring 2003 04 25 2003 Georgia Institute of Technology School of Electrical and Computer Engineering Table of Contents 1 Abstract 3 2 Introduction 4 2 1 General Background 4 2 2 The Gigabit Ethernet Standard IEEE 802 3z 4 2 3 Design Project Overview 5 2 4 Group Management 6 3 Board Layout and Design 6 3 1 Design Tools 6 3 2 Transceiver Schematics 7 3 3 Board Layout 8 3 4 Design Overview 11 3 5 Second Layout and Design 11 4 Testing 13 4 1 First Round 13 4 2 Second Round 15 4 3 Attenuation Testing 17 5 Alignment Tolerance 19 6 Financial Budget and BOM 21 6 1 Financial Budget 21 6 2 Bill of Materials 22 7 Conclusions 23 8 References 26 9 Appendix A Optical Link Budget 28 10 Appendix B Figures and Waveforms 36 2 1 Abstract The field of modern communications has an ever increasing need for improved means of data transfer with emphasis on high speed and high quality technologies The goal of this project is to design implement and test a Gigabit Ethernet optoelectronic link that will work at a frequency of 1 25 GHz and perform well under attenuation The project deals with the design of a transceiver board which transmits data at a Gbps gigabits per second rate The essence of the design is to calculate the transmitting laser s bias currents and implement filtering circuits to avoid electronic noise on the component Upon completion of the design it is fabricated and soldered on a PCB board and then tested for performance and accuracy with and without attenuation The PhotoDetector s alignment tolerance is also estimated via measurements Conclusions are drawn as to the significance of the results and the importance of the design project The role of the technology in the real world and the implications of the design are also discussed in an attempt to generalize the topic into a bigger picture and draw conclusions beyond the scope that is presented 3 Introduction 2 1 General Background Modern organizations depend upon their local area networks LANs to provide connectivity for a growing number of complex mission critical desktop computing applications As the volume of network traffic increases however the bandwidth offered by a typical 10 Mbps Ethernet LAN quickly becomes inadequate to maintain acceptable performance for a growing number of desktop server computing environments These traffic jams are fueling the need for higher speed networks The most appropriate solution is Gigabit Ethernet Gigabit Ethernet provides 1 Gbps bandwidth for campus networks with the simplicity of Ethernet at lower cost than other technologies of comparable speed It offers a natural upgrade path for current Ethernet installations leveraging existing end stations management tools and training The simple migration and support offered by Ethernet combined with the scalability and flexibility to handle new applications and data types makes Gigabit Ethernet the strategic choice for highspeed high bandwidth networking Gigabit Ethernet is an extension to the highly successful 10 Mbps and 100 Mbps IEEE 802 3 Ethernet standards Offering a raw data bandwidth of 1000 Mbps Gigabit Ethernet maintains full compatibility with the huge installed base of Ethernet nodes 2 2 The Gigabit Ethernet Standard IEEE 802 3z The key objectives of the 802 3z Gigabit Ethernet task force were to develop a Gigabit Ethernet standard that does the following Allows half and full duplex operation at speeds of 1000 Mbps Uses the 802 3 Ethernet frame format Addresses backward compatibility with 10BASE T and 100BASE T technologies There were three objectives for link distances a multimode fiber optic link with a maximum length of 500 meters a single mode fiber optic link with a maximum length of 5 kilometers and a copper based length of 25 meters The challenges associated with using lasers on multimode fiber have become more apparent as the operating speed has increased In addition the IEEE 802 3z task force was particularly attentive to the characteristics of the installed base of networking cabling be it copper or fiber optic cabling It was discovered that a jitter component caused by a phenomenon known as differential mode delay DMD With 1000BASE LX transceivers over multimode fiber external patch cords are used to mitigate DMD 4 The initial applications for Gigabit Ethernet are for campuses or buildings requiring greater bandwidth between routers switches hubs repeaters and servers Examples include switch to router switch to switch switch to server and switch toswitch connections 2 3 Design Project Overview The primary goal of our group is to design and implement a functional Gigabit Ethernet and Eye Safety compliant optoelectronic transceiver Once a working link has been built the secondary goal is to optimize the link for error free data transfer using the most affordable design During the course of the project the group members will follow a self assigned task and time management plan The design must be carried out on a 350 budget allowance provided by the Georgia Tech ECE department A system level design topology is provided by the instructors and recommended as guidance for the system design As an initial step a receiver board is provided without optical photo detector circuitry After the electrical only receiver board is assembled and tested the group must design photo detector circuitry to integrate with the provided receiver design Finally the group will design an optical transceiver circuit which interfaces and combines the transmitter with the optical receiver on the same board Vertical Cavity Surface Emitting Laser diodes VCSELs are an integral part of this project and feature in the Tx design They are a relatively new class of semiconductor lasers that emit light perpendicularly from the wafer and are composed of layers of partially reflective mirrors which confine the light For this project VCSELs will be assessed by divergence angle threshold current and slope efficiency Photo detectors PDs form the beginning of the Rx module They capture and convert the optical signal into an electrical one maintaining the data present in the original stream High responsivity low capacitance and bigger receiver area are the critical characteristics required in a photodiode for a good optoelectronic link The optical fibers used are multimode types functioning at the