SPRS174S – APRIL 2001 – REVISED MARCH 2011
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6.30.8 Definitions of Specifications and Terminology
Integral Nonlinearity
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 1/2 LSB before the first code transition. The full-scale point is
defined as level 1/2 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.
Differential Nonlinearity
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 Offset
The major carry transition should occur when the analog input is at zero volt. Zero error is defined as the
deviation of the actual transition from that point.
Gain Error
The first code transition should occur at an analog value 1/2 LSB above negative full scale. The last
transition should occur at an analog value 1 1/2 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 (SINAD)
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 (ENOB)
For a sine wave, SINAD can be expressed in terms of the number of bits. Using the following formula,
(SINAD
-
1.76)
N
=
6.02
it is possible to get a measure of performance expressed as N, the effective number of bits. Thus,
effective number of bits for a device for sine wave inputs at a given input frequency can be calculated
directly from its measured SINAD.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of the first six harmonic components to the rms value of the measured
input signal and is expressed as a percentage or in decibels.
Spurious Free Dynamic Range (SFDR)
SFDR is the difference in dB between the rms amplitude of the input signal and the peak spurious signal.
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Electrical Specifications
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