Integral nonlinearity refers to the deviation of each individual code from a line drawn from zero through full scale. The point used as zero occurs one-half LSB before the first code transition. The full-scale point is defined as level one-half LSB beyond the last code transition. The deviation is measured from the center of each particular code to the true straight line between these two points.
An ideal ADC exhibits code transitions that are exactly 1 LSB apart. DNL is the deviation from this ideal value. A differential nonlinearity error of less than ±1 LSB ensures no missing codes.
Zero error is the difference between the ideal input voltage and the actual input voltage that just causes a transition from an output code of zero to an output code of one.
The first code transition should occur at an analog value one-half LSB above negative full scale. The last transition should occur at an analog value one and one-half LSB below the nominal full scale. Gain error is the deviation of the actual difference between first and last code transitions and the ideal difference between first and last code transitions.
Signal-to-Noise Ratio + Distortion
Signal-to-noise ratio + distortion (SINAD) is the ratio of the rms value of the measured input signal to the rms sum of all other spectral components below the Nyquist frequency, including harmonics but excluding DC. The value for SINAD is expressed in decibels.
Effective Number of Bits
For a sine wave, SINAD can be expressed in terms of the number of bits. Using the formula it is possible to get a measure of performance expressed as N, the effective number of bits (ENOB). Thus, the ENOB for a device for sine wave inputs at a given input frequency can be calculated directly from its measured SINAD.
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the rms sum of the first nine harmonic components to the rms value of the measured input signal and is expressed as a percentage or in decibels.
Spurious Free Dynamic Range
Spurious free dynamic range (SFDR) is the difference in dB between the rms amplitude of the input signal and the peak spurious signal.