AD4080BBCZ datasheet(17/95 Pages) AD

17 / 95 page

Data Sheet

AD4080

TERMINOLOGY

analog.com

Rev. 0 | 17 of 95

Integral Nonlinearity Error (INL)

INL refers to the deviation of each output code from a line drawn

between points at negative full scale and positive full scale. The

negative full-scale reference is defined by an input level equivalent

to ½ LSB prior to the first code transition. The positive full-scale

reference is defined as an input level that is 1½ LSB beyond the

last code transition. The deviation is measured from the center of

each code relative to the straight line.

Differential Nonlinearity Error (DNL)

In an ideal ADC, code transitions occur at 1 LSB intervals. DNL is a

measure of the maximum deviation of any code from the ideal code

width. DNL is specified in terms of resolution for which no missing

codes are guaranteed.

Zero Error

Zero error is the difference between the ideal midscale voltage, 0 V,

and the applied voltage producing the midscale output code, 0 LSB.

Gain Error

Gain error is specified as the difference in the slope of the ADC

transfer characteristic vs. that of an ideal converter. In an ideal data

converter, the first code transition (100 … 00 to 100 … 01) occurs

½ LSB more than the nominal negative full-scale input (−2.999997

V for a ±3.0 V range at 20 bits) and the last code transition (011

… 10 to 011 … 11) occurs 1½ LSB less than the nominal positive

full-scale input (+2.999991 V for a ±3.0 V range at 20 bits).

Signal-to-Noise Ratio (SNR)

SNR is the computed ratio of the fundamental signal amplitude

measured in RMS volts and the root sum of squares of all other

spectral components in the Nyquist bandwidth (f < fS/2) excluding

harmonics and DC components. The computed value of SNR is

converted into a logarithmic scale and expressed in decibels (dB).

Signal-to-Noise-and-Distortion (SINAD) Ratio

SINAD is the computed ratio of the fundamental signal amplitude

measured in RMS volts and the root sum of squares of all other

spectral components in the Nyquist bandwidth (f < fS/2) including

harmonic components but excluding the DC component. The com-

puted value of SINAD is converted into a logarithmic scale and

expressed in decibels (dB).

Total Harmonic Distortion (THD)

THD is the ratio of RMS sum of the amplitudes of the first five

harmonic components to the RMS amplitude of a full-scale input

signal expressed in decibels (dB).

Spurious-Free Dynamic Range (SFDR)

SFDR is the ratio between the RMS amplitude of the input signal

and the peak spurious signal amplitude, expressed in decibels (dB).

Intermodulation Distortion

With inputs consisting of sine waves at two frequencies, fA and

fB, any active device with nonlinearities creates distortion products

at sum and difference frequencies of m × fA and n × fB, where

m, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms are

those for which neither m nor n are equal to 0. For example,

the second-order terms include (fA + fB) and (fA − fB), and the

third-order terms include (2fA + fB), (2fA − fB), (fA + 2fB), and (fA −

2fB).

The AD4080 is tested where two input frequencies near the top

end of the input bandwidth are used. In this case, the second-order

terms are usually distanced in frequency from the original sine

waves, and the third-order terms are usually at a frequency close to

the input frequencies. As a result, the second-order and third-order

terms are specified separately. The calculation of the intermodula-

tion distortion is as per the THD specification, where it is the ratio

of the RMS sum of the individual distortion products to the RMS

amplitude of the sum of the fundamentals, expressed in decibels.

Power Supply Rejection Ratio (PSRR)

PSRR is a measure of the sensitivity of the ADC to variations in the

specified power supply rail vs. frequency. PSRR is computed as the

ratio of the observed change in the output code in RMS volts to the

RMS magnitude of the perturbing signal coupled to the supply. The

resulting ratio is reported in decibels (dB).

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