Noise degrades ADC resolution and the histogram tool is used to estimate Effective Resolution, which is an indicator of the number of bits of ADC resolution lost due to noise generated by the various sources connected to the ADC when measuring a DC signal. The cumulative effect of noise coupling to the ADC output from sources such as the input drive circuits, the reference drive circuit, the ADC power supply, and the ADC is reflected in the standard deviation of the ADC’s output code histogram, obtained by performing multiple conversions of a DC input applied to a given channel.

The histogram analysis corresponding to a DC input is displayed by selecting Histogram Analysis on Pages and clicking on the Capture button as shown in Figure 4-6. The Analysis results include Mean, Sigma, Min Code, Max Code, and Code spread.

The X Scale of Histogram Analysis results are changed by selecting Auto mode or the default Fit to code range in the top right area, which is similar as the Y scale fit in the Time Domain Display tool.

Figure 4-6 Histogram Analysis Tool