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Probing high speed digital circuits

  1. Aug 23, 2010 #1
    I have a 100MHz bus going from CPU to Memory. The routing length is about 2inches. So there is no termination.
    When I hook up the bus to a Logic analyzer, how do I know the Logic analyzer probes are not causing any reflection and messing up the bus signals. The length of the probe is about 40inches(1meter).
    The probes are connected to wires(~4inches) that are soldered to the bus traces on the PCB.
    What would be the right way to probe these signals.
     
  2. jcsd
  3. Aug 24, 2010 #2

    berkeman

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    Staff: Mentor

    The logic analyzer probe head should have a high-impedance adapter thing. What logic analyzer are you using? What adapter modules are available for it? For the old HP 16500 logic analyzers that we have in the lab, the adapter modules are 01650-63201 (or -63203):

    http://www.nationaltestequipment.com/unitDetails.cfm?modelID=8805

    .
     
    Last edited by a moderator: Apr 25, 2017
  4. Aug 24, 2010 #3
  5. Aug 24, 2010 #4

    berkeman

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    Staff: Mentor

    The P6410 manual at the Tek website shows the equivalent circuit for the probe points as 2pF // 20kOhms. That should not load your bus signals too much. Be sure to keep the connections short between the bus and the probe.
     
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