Cirrus Logic AN330 REV2 - Manual (Page 11)

AN330REV2 11
AN330
An example which uses the 256 samples from the CS3001-CS5513 circuit yields the following result:
One can then use the Chart Wizard in the Excel application and the Column Chart option to plot the Frequency data
like this:
From the plot one can easily see that the data exhibits a Normal (also called Gaussian or bell-shaped distribution)
which is what should be expected if one is observing thermal noise. The histogram shows that the peak-to-peak
code variation from the CS3001/CS5513 circuit is 12 codes. If this is divided into the 267387 codes used in the
converter across the 2.04 volt input span, the result is 22,282 noise-free counts, which is close to what was calcu-
lated (21,935). The Excel software was used earlier to compute the standard deviation at 1.8 codes. By multiplying
the standard deviation by 6.6 (±3.3 standard deviations), the result is 11.88 codes, which agrees with the peak-to-
peak range illustrated in the plot of 12 codes.