Cirrus-logic AN330 REV2 Manuel d'utilisateur télécharger pdf (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.

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Cirrus-logic AN330 REV2 Manuel d'utilisateur Page 11