Gigabit Ethernet: An Affordable Solution Preliminary Design

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Gigabit EthernetAn Affordable
SolutionPreliminary Design

• G4
• Gaurav Asthana
• James Denaro

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Part I Extraction of Optomodule

• D-Link DGE-550SX Fiber Gigabit Adapter
• High-bandwidth network adapter
• up to 2000Mbps full-duplex bandwidth capacity
• incorporates the Agilent HFBR-53D5 fiber optic
  transceiver
• 850 nm Vertical Cavity Surface Emitting Laser
  (VCSEL) in an optical subassembly (OSA) which
  mates to the fiber cable

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Part I Extraction of HFBR-53D5

• Desolder the opto-module from the D-link card and
  mount it on a custom board

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Implementation of bias network for the optical
transceiver

• Pins 2 and 3 require inputs to come in on 50?
  lines and to be de-coupled using 0.01?F
  capacitors. Similarly, pins 7 and 8 transmit on
  50? lines that are de-coupled by 0.01?F
  capacitors.

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Components

• SMA has functionality up to 1000 MHz.
• Surface mount capacitors and resistors.
• Saves space but more difficult soldering of these
  on the board since these parts are very small and
  difficult to handle.
• To connect the optical transceiver module to the
  D-link card, we need a cable with a 50?
  resistance. We need a 50? cable to impedance
  match the system and avoid signal reflections.

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Part II Integration of Maxim Parts

• Maxim transimpedance (MAX3266EV) and limiting
  amplifiers (MAX3264EV )

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MAX3266EV TIA
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MAX3266EV TIA Bias Network

• Important design considerations include the
  following parameters
• INPUT should approximate 50mVp-p.
• OUT and OUT- need 50? terminations.
• The connector at INPUT is terminated with 50? to
  ground.
• The device operates from a 3.0V to 5.5V single
  supply and requires no compensation capacitor.

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MAX3264EV Limiting Amplifier

• Important design considerations include the
  following parameters
• The output current can be set for either of two
  levels. (16mA or 20mA)
• The device operates from a 3.0V to 5.5V single
  supply
• Potentiometers R3, R4, R12, and R13 adjust the
  VTH voltage.

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Combination
The MAX3266 chip providing transimpedance
amplification must be mated to the MAX3264
post-amplifier. A typical application of the
MAX3266 in conjunction with a limiting amplifier
such as the MAX3264 is shown below. These
connections will be made using SMA connectors and
appropriately impedance matched wires.
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Part III Custom Board

• Post-Amp Output
• 0 ? 1300 mV
• TIA Input
• -150 ? 150 uA
• Potential Issues
• The MAXIM transimpedance preamplifier has singled
  ended. Therefore we must use either the Tx or
  Tx- outputs of the optical module (but not both)
  for connection. This may lead to reduced signal
  to noise ratio.