- **Power Supplies**
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- - **Noise Fourrier Transform (FFT)**
(*http://www.diyaudio.com/forums/power-supplies/65899-noise-fourrier-transform-fft.html*)

Noise Fourrier Transform (FFT)Is the following correct?
IF [list=1][*]an op-amp has a listed voltage noise of 3 nV/rqrtHz[*]used with a gain of 100[*]the conditions are such that the voltage noise dominates[*]further ignore 1/f and just consider wideband white noise[*]I take the FFT of the output noise[/list=1] THEN the noise floor should be observed at 3nV * 100 = 300nV = -130 dB AND the rms voltage is equal to 3nV* sqrt(bandwidth) |

there is an additional BW effect in the fft definition, if the bin size is ~ 1 Hz then your estimate is roughly correct - figure bin size from time duration of data set/#points in fft
also be aware that various math packages use different normalizations; you may see 1/n or sqrt(n) used input refered noise is en*sqrt(bw) output noise will be 100x larger it is quite an accomplishment to totaly remove power line fundamental and harmonics at these levels |

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