Introduction and Review of Statistics 11 convert back to voltage by taking the square root of the result. Note that we get the proper units. Also note that power spectral density is simply the voltage or current spectral density squared (remember P V 2 /R and P I 2 R). Thus, by looking at Figures 1.17 and 1.18, you can see why power spectral density must be integrated rather than voltage or current spectral density. Chapter Summary l l l Oscilloscope measurements show noise in the time domain. x-axis is time and y-axis is voltage or current. A Gaussian distribution is a statistical view of noise. l Standard deviation and RMS are the same if noise does not have a DC component (average value is zero). l Six times the standard deviation is a good estimate of peak-to-peak noise. l There is a 99.7% probability that noise will be less than six times the standard deviation. l Most noise is uncorrelated. l Uncorrelated noise is added with the root sum of the square of each noise component. The noise spectral density is a frequency domain view of noise. l Spectral density has units of V/ Hz or A/ Hz. l