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• Component selection

  Christoph Tack • 09/18/2019 at 20:17 • 0 comments

  DC/DC converter

  Powering the AD8129

  The original plan was to use a 5V to +12/-12V converter.  The problem with this high supply voltage is that schottkey diodes need to be added to protect the differential inputs.  These will lead to extra leakage and thus measurement errors especially when measuring small currents.

  The solution is to use an MDD02L-09 or equivalent power supply.  This limits the common mode range to +7V/-7V.

  Differential amplifier

  ADA4622-1

  Ideally suited as transimpedance amplifier.

  Maximum output current when used as transimpedance amplifier?
  

  AD4927-1

  • 2.3GHz -3dB bandwidth

  AD8129

  • 200MHz -3dB bandwidth
  • +10V/-10V CM-range
  • +0.5/-0.5 DM-range
  • 250nA input bias current -> not suited for measuring µA-range currents
  • Gain = +10 (can be adjusted)

  AD8479

  • 130kHz -3dB bandwidth
  • +/- 600V CM-range
  • 500kohm Zin(CM), 2Mohm Zin(DM)
  • Gain = +1

• Housing

  Christoph Tack • 09/09/2019 at 18:25 • 0 comments

  Miniature Plastic USB Enclosures (1551USB Series)

  • DWG files from manufacturer can be converted to DXF with https://cloudconvert.com/dwg-to-dxf.
  • After cleanup with LibreCAD and a check for the correct scale, the file can be imported in EasyEDA.

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