36.5 ADC Parameter Definitions
An ideal n-bit single-ended ADC converts a voltage linearly between GND and
VREF in 2n steps (LSb). The lowest code is read as
‘
0’, and the highest code is read as ‘2n-1’. Several
parameters describe the deviation from the ideal behavior:- Offset Error
- The deviation of the first transition (0x000 to 0x001) compared to
the ideal transition (at 0.5 LSb). Ideal value: 0 LSb.
Figure 36-1. Offset Error 
- Gain Error
- After adjusting for offset, the gain error is found as the deviation
of the last transition (e.g., 0x3FE to 0x3FF for a 10-bit ADC) compared to the
ideal transition (at 1.5 LSb below maximum). Ideal value: 0 LSb.
Figure 36-2. Gain Error 
- Integral Nonlinearity (INL)
- After adjusting for offset and gain error, the INL is the maximum
deviation of an actual transition compared to an ideal transition for any code.
Ideal value: 0 LSb.
Figure 36-3. Integral Nonlinearity 
- Differential Nonlinearity (DNL)
- The maximum deviation of the actual code width (the interval between
two adjacent transitions) from the ideal code width (1 LSb). Ideal value: 0
LSb.
Figure 36-4. Differential Nonlinearity 
- Quantization Error
- Due to the quantization of the input voltage into a finite number of codes, a range of input voltages (1 LSb wide) will code to the same value. Always ±0.5 LSb.
- Absolute Accuracy
- The maximum deviation of an actual (unadjusted) transition compared to an ideal transition for any code. This is the compound effect of all errors mentioned before. Ideal value: ±0.5 LSb.