Questions about Johnson Noise

Discussion in 'General Electronics Chat' started by Hassan mahmoud, Jan 24, 2016.

  1. Hassan mahmoud

    Thread Starter New Member

    Jan 23, 2016
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    1. Is this noise consider DC Noise? Could I remove it with a cap?
    2. Based on formula an infinite resistor will cause an infinite voltage noise, and zero current noise. Well, it's obvious that there is a contradiction here since the open circuit(which is infinite resistor) isn't produce an infinite noise. Could someone explain?
    3. The equation tells that the short circuit with infinite bandwidth will cause noise approaches to infinity. How much is that correct?
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    You know the term but, clearly, you haven't done much research.

    In answer to your first question, Johnson Noise (also referred to as Thermal Noise) is related to charged carrier movement in a resistance. It is also in the categories of noise considered White Noise which are uniformly distributed across frequency. So no, it can't be filtered with a cap.

    #2 That's the theory, but it makes no sense in the real world.

    #3 Infinite bandwidth has little application in the real world.
     
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  3. Hassan mahmoud

    Thread Starter New Member

    Jan 23, 2016
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    Thanks for the reply.
    According to #3, Actually, this is the first time that there is bandwidth in real world. Anyway, for what ranges of Resistor and bBandwidth, the equations is valid?
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    I'd think that it would hold for anything within reason; i.e. no zero/infinity resistance and/or bandwidth. Things might also get interesting at, or near, absolute zero.
     
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