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Background on Gigabit Ethernet

Background on Gigabit Ethernet. ECE 4006 C G3: Karen Cano , Scott Henderson , Di Qian Dec, 5 2002. Ethernet History (Timeline). 1973 – (2.94Mbps) First developed at Xerox’s Palo Alto Lab (Robert Metcalfe and David Boggs)

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Background on Gigabit Ethernet

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  1. Background on Gigabit Ethernet ECE 4006 C G3: Karen Cano, Scott Henderson, Di Qian Dec, 5 2002

  2. Ethernet History (Timeline) • 1973 – (2.94Mbps) First developed at Xerox’s Palo Alto Lab (Robert Metcalfe and David Boggs) • 1979 - (10Mbps) Improvement by DEC, Intel and Xerox. The DIX standard. Thick Ethernet System • 1983 - Formally standardized as IEEE 802.3

  3. Timeline (con’t) • 1983–1989 – Improvements on bus topology and transmission distance. • 1990 – version IEEE 802.3i, 10Base-T technology. • 1995 - (100Mbps) version IEEE 802.3u, also call “Fast Ethernet”.

  4. Timeline (con’t) • 1998 – (1 Gbps) version IEEE 802.3z, fiber optics; and IEEE 802.3ab, twisted pair. Also know as “Gigabit Ethernet”. • Present – (10 Gbps) standard completed in 2002.

  5. Project Tasks • 1. Research on the transmitting and receiving modules. • 2. Examine the testing board • 3. Search for the components • 4. Testing the evaluation board with purchased components • 5. Connecting the purchased components with parts from other groups.

  6. Project Goal • Duplicate the data transmitting and receiving module functionality of the Gigabit Ethernet technology with purchased components that provide optimum performance at a minimum price.

  7. Possible Solutions • Transmitting module (laser source) • VCSEL • Receiving module (Photo-detector) • PIN photodiode • Other Specs: - SC connectorized (optical) - SMA connectorized (electrical) - 850nm - Multimode (fiber) - relatively low cost

  8. Laser Basics • What is a Laser? • Light Amplification by Stimulated Emission of Radiation • How? 1) Electrons in low-energy levels bumped into high levels by injection of energy 2) When an electron drops to a lower energy level, excess energy is given off as light.

  9. VCSELs • Vertical Cavity Surface Emitting Lasers • Physical makeup • Bragg mirrors • Active region • Fabrication techniques • Molecular beam epitaxy • Vapor phase epitaxy

  10. VCSELs • In EELs no pre-cleaving tests can be performed, testing VCSELs is much cheaper • Less current required for VCSELs • Output beam easier couple into fiber and much less divergent than EELs • Smaller and faster than EELs

  11. VCSELs vs. EELs • Edge Emitting Lasers - give out their light from the sides or edges, therefore no pre-cleaving tests can be performed • Since VCSELs emit light from the top and bottom, they do not have this problem. Testing them is much cheaper

  12. Interesting Facts • In a typical VCSEL, as many as 60 individual semiconductor layers are stacked within a structure 10 microns thick. • 20,000 individual laser die can be fabricated on a single 3 inch wafer.

  13. Multimode • Multimode- light is injected into the core and can travel many paths through the cable (i.e. rattling in a tube). • Each path is slightly different in length, so the time variance this causes, spreads pulses of data out and limits the bandwidth.

  14. Singlemode • Fiber has such a narrow core that light takes one path only through the glass. • Not limited to modal-bandwidth. • Very small amount of pulse-spreading is consequential only in Gigabit speed applications.

  15. Photodetectors • Necessary for light pulse detection • Wide variety of of types • Photoconductors • Avalanche photodiodes • PIN photodiodes • MSM photodiodes

  16. Photoconductors • Operation based on varying conduction • Many important factors affecting bandwidth • Transit time • Surface area of photon acceptor region • Noise ratio (Johnson noise) • Quantum efficiency

  17. Avalanche Photodiodes • Exemplify the “gain-bandwidth” tradeoff • Use the p-n junction model to operate • Take advantage of the avalanche effect • Carrier multiplication • Associated gain • Time constant associated with avalanche • Bandwidth penalty

  18. PIN Photodiode • PIN • Reason for name • Doped region, undoped region, doped region • Unity gain • Functions under reverse bias • Most important parameter for operation • Transit time

  19. Bandwidth vs. Depletion Width • Transit time • Time for subatomic particle to get from one electrode to the other • Based on quickest, typically electron • e- mobility > h+ mobility • Capacitance limited

  20. Transit Time (continued) • Dependence on intrinsic region length • Minimizing this region • High bandwidth applications

  21. MSM Photodiode • Metal-Semiconductor-Metal • Associated work functions • Atomic level metal-semiconductor marriage • High speed (up to 100GHz) • Majority carrier devices • Not developed for Gigabit Ethernet on scale as large as PIN

  22. Concluding, thus far….. • Obvious choices for devices: • VCSEL@850nm • PIN photodiode w/ acceptable bandwidth • Multimode fiber • SC optical connectors • SMA electrical connectors • Gigabit Ethernet is a popular application • If you are buying less than five-million devices then be prepared to stand at the end of the line.

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