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

Question

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?

ScottH · Accepted Answer

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 = e n,wideband *√ f H - f L + f C *ln(f H /f L ) 
 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, f H >> 10*f C . 
 You may also be able to do the rms noise calculation faster with a SPICE simulator. See the webcast slides for the full equation.)