INL (integrated non-linearity) and DNL (differential non-linearity) are key ADC parameters that indicate accuracy. INL error is the deviation of the actual transfer characteristic from an ideal straight line. It is calculated after offset and gain errors have been removed. INL is often called ‘relative accuracy.’ In the graph on the bottom left, the red line represents the ideal ADC output from a straight line input and the blue line represents the actual output code of the ADC. The DNL error is the difference between an actual step width and the ideal value of 1 LSB. Any deviation from 1 LSB is defined as DNL. DNL is simply the difference between two measured steps. If the DNL is greater than 1 LSB, the output gets smaller for an increase on the input. The graph on the bottom right shows how DNL is calculated.