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Calculating Input Noise Voltage

Discussion in 'Electronic Basics' started by MRW, May 31, 2007.

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  1. MRW

    MRW Guest

    I was just checking out various opamp datasheets. I encountered this

    In the few lines of text, it says that the input noise voltage is 9 nV/
    sqrt(Hz) at 10kHz. But in the table at the bottom of the page, it says
    that the input noise voltage is 18 nV/sqrt(Hz) at 1kHz.

    How did they calculate this?

    I'm curious because if I were to use an opamp (not necessarily this
    one) then I would like to know how much input noise voltage it
    contributes for a certain bandwidth, for instance audio band from 20Hz
    to 20kHz. There was another discussion that I saw (don't remember the
    link) that mentioned that at one particular design, the amplifier was
    designed with a 40dB gain and the input noise got amplified to about
  2. Phil Allison

    Phil Allison Guest

    "MRW" <>

    ** Groper fool alert.

    ** See figure 19 ??

    See how the EIN goes up dramatically at frequencies below 3 kHz ?

    Go check some other op-amps - discover they are not all like that.

    ** Normally just multiply the typical or 1 kHz EIN figure by 141 (= sq
    rt 20,000)

    ........ Phil
  3. MRW

    MRW Guest

    Thanks, Phil! I'll take a look at other datasheets. Got any opamps you
    can recommend for audio?
  4. Phil Allison

    Phil Allison Guest

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