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# 6/1/16: signal bandwidth is spread across both wideband and 1/f

You mentioned the noise calculation in the wideband and 1/f regions, what do you do when the signal bandwidth is spread across both regions?

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[edited by: lallison at 3:55 PM (GMT -4) on 6 Jun 2022]
• Some literature says to break the calculation up into the 1/f noise below the corner frequency and the white noise above the corner frequency and add them together. The easier and slightly more accurate way is to add (as root-sum-of-squares) the 1/f noise and the white noise contribution assuming that there is 1/f noise and white noise everywhere, which gives you the following equation:

rms noise = en,wideband*√fH - fL + fC*ln(fH/fL)

If you start playing with the numbers, you will find that white noise quickly starts to dominate. Most of the literature will tell you to ignore 1/f if the -3dB bandwidth of your circuit is significantly more than 10 times the corner frequency, fH >> 10*fC.

You may also be able to do the rms noise calculation faster with a SPICE simulator. See the webcast slides for the full equation.