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The calculation of noise bandwidth

Cera Wei
Intellectual 2010 points

Hi, I'm learning the op-amps now, and have a question for the calculation of noise bandwidth:

For the convenience of the calculation, the low fass filter often equivalent to the rectangular filter, called  called a brick wall filter, which has the same area as the low pass filter. BW=Kn*fc. The calculation of Kn is shown below, but the result is different with the given Kn, why?

Thank you!

  • 0
    TI__Guru 62715 points

    Hello,

    We're having a little trouble following your math, but I believe your final calculation for Kn for a 1st order filter is 10^1.5, or 31.62.  That would mean the effective bandwidth of a 1kHz filter is 31.62kHz which is way too large.

    I think your errors come from the fact that the integration calculation used to determine the area under the curve requires the use of linear (not logarithmic) units.