Help interpreting noise graphs

Discussion in 'General Electronics Chat' started by daviddeakin, Aug 12, 2011.

  1. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
    207
    27
    I am confused about the output noise current graph in the LM13700 data sheet (page 6), and this sort of graph in general.

    http://www.media.mit.edu/resenv/classes/MAS836/ToPost/LM13700.pdf

    For example, it says that for a bias current of 1mA, the noise output noise current is 200pA per ^/Hz at 1kHz. Can someone explain what this means?

    For example, to get the RMS noise across some bandwidth I need to multiply the amps-per-root-hertz by the square root of the bandwidth, right? So for a 20kHz bandwidth I would get 200pA*141 = 28nA RMS noise current.
    But the graph is a curve, so I would get a completely different figure if I chose a different frequency from the graph, so how should I be using these figures? :confused:
     
    Last edited: Aug 15, 2011
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