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Resistor 'absorbs' oscillation?

  1. Dec 2, 2009 #1
    I have a tiny bit of current fluctuation on one of my lines. If i put a lil 500ohm resistor in the line the osillations on the other end substantially decrease.

    Why?

    Does the resistor effectively 'absorb' these oscillations?
     
  2. jcsd
  3. Dec 2, 2009 #2

    Integral

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    It is hard to say much without some knowledge of the circuit. If you could tell us more it would help.
     
  4. Dec 2, 2009 #3
    If you are talking about standing waves (oscillations) in transmission lines, then terminate the t-line with its characteristic impedance; e.g., 50 ohms for RG-58. A t-line that is open at one end has a current node (voltage maximum) at the end, and reflects the forward signal..
    Bob S.
     
  5. Dec 2, 2009 #4
    Thanks for the replies.

    Specifically I'm talking about a X96010 programmable current generator. My suspicion is that the analog temperature driven Vsense for this device is a bit unstable, normally unnoticable, but because there is a high speed LT1394 comparator with a relatively small hysteresis in the design, becomes a problem right around the switch point (otuput oscillates).

    Might also have to do with the fact that the X96010 basically acts as an ADC, and I might be flopping between bytes.

    Eithe way it is causing some current fluctuation, which seems to be improved if i put an (arbitrary) 499ohm resistor in the line. I'm trying to understand the fundamental reason for the improvement.
     
  6. Dec 2, 2009 #5
    Depending on how long your line is, you could be suffering from oscillation between the source and line. Every line has a capacitance and if you switch a voltage vary quickly into that line, a current spike can be created. What it seems like is happening is that spike is bouncing back and forth between the line and your source; by adding the resistor (in series right?), you are slowing the rate at which the capacitance is charged, reducing the oscillation.
     
  7. Dec 2, 2009 #6
    Yes the resistor is in series. Very interesting, thank you.
     
  8. Dec 2, 2009 #7
    heres the pic, the current from the x96010 is what i believe osillates
     

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  9. Dec 2, 2009 #8
    If the line from the x96010 is a twisted pair, I would out a ~70 ohm resistor upstream of the 0.1 uF capacitor. This plus the capacitor will be an effective termination for the twisted pair.
    Bob S
     
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