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LeCroy or Tek scope?

Discussion in 'Electronic Design' started by Klaus Bahner, Mar 5, 2004.

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  1. Jim Yanik

    Jim Yanik Guest

    the inductance of a too-long ground lead will cause false ringing.
     
  2. John Larkin

    John Larkin Guest

    If you plug one of those small 950-ohm Caddock non-inductive resistors
    into the end of an SMA female, you get a nice 6 GHz 10:1 passive
    probe. Even a carbon comp works pretty well.

    And a good fet probe is magical; you can probe a lot of ecl-type
    circuits with no ground clip at all. I should think that a homemade
    GaAs fet probe wouldn't be hard to make... maybe use one of the neat
    NEC dual-gates, NE25x39, with g2 to source for really low Cin.

    The best is an SD-14 sampling probe, something like 0.2 pF at the tip.

    John
     
  3. dated Sun, 07 Mar 2004 10:55:25 -0800,
    I think you need a Z0 termination at both ends of the coaxial
    cable.
     
  4. John Larkin

    John Larkin Guest


    You need it at the scope end, but not at the tip. The scope-terminated
    coax looks like a near-perfect 50 ohm resistor at the far end, so the
    950 ohm resistor feeding into the coax looks like a flat 20:1 (oops...
    not 10:1) voltage divider. 450 ohms gives 10:1.

    That's how the Agilent 54006A probe works.

    John
     
  5. dated Sun, 07 Mar 2004 15:04:02 -0800,
    You are right, if there is no reflexion from the scope then
    you dont need 50 ohms on the tip side.
     
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