Resistor Current Noise

Discussion in 'The Projects Forum' started by bonkers31, May 27, 2016.

  1. bonkers31

    Thread Starter New Member

    May 27, 2016
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    Hey all, I'm trying to measure 1/f noise from a resistor (using a bridge) connected to an op-amp, but for some reason I'm getting a region of white noise at a higher noise voltage than predicted (from thermal or shot). After this region it also returns to being pink again, not really sure why. Any help would be greatly appreciated, Thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
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    What type of resistor?
    Perhaps you are looking at the op amp noise which is likely higher than the resistor noise.
     
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  3. bonkers31

    Thread Starter New Member

    May 27, 2016
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    I measured the op-amp noise and its much smaller so seems unlikely. I'm using a 10^5 ohm bridge
     
  4. bonkers31

    Thread Starter New Member

    May 27, 2016
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    thin film
     
  5. crutschow

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    How was the op amp connected when you made the measurement?
     
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  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Is your circuit shielded to exclude EM radiation? Any radio or TV stations within 50 miles? Digital program modulation is a different beast from analog broadcasting. It might appear as white noise in certain freq. ranges.
     
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  7. crutschow

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    That's an interesting thing about digital modulation. For optimum usage of RF spectrum, the modulation should look like white noise, since that means the entire allotted modulation spectrum is being uniformly used, and modern digital modulation approaches that ideal.
    AM modulation, on the other hand, tends to have a spectrum that looks like a comb, with the frequencies in between the comb peaks not well utilized.
     
  8. bonkers31

    Thread Starter New Member

    May 27, 2016
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    I don't belive there's any radio or TV stations near by. I did shield the op amp and bridge in a grounded metal box though.
     
  9. bonkers31

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    May 27, 2016
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    How do you mean? I used an AD620 with the gain set to 100 if that helps
     
  10. bonkers31

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    May 27, 2016
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    I excited the bridge with a DC bias, zeroing the offset by connecting the bridge to a variable resistor and then recorded AC noise voltage from oscilloscope
     
  11. crutschow

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    I mean how did you connect the op amp when you measured its noise?
     
  12. bonkers31

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    May 27, 2016
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    It was exactly the same as when measuring with the bridge, just with the bridge removed. I have been looking around online as well, is it possible it could have occurred due to LC/RLC oscillation?
     
  13. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Maybe a schematic??
     
  14. crutschow

    Expert

    Mar 14, 2008
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    Okay, let's try again. :confused:
    What, if anything was connected to the op amp input?
    Post a circuit diagram for the op amp during this test.
     
  15. bonkers31

    Thread Starter New Member

    May 27, 2016
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  16. crutschow

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