AD4884BBCZ datasheet(26/116 Pages) AD

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Data Sheet

AD4884

TERMINOLOGY

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Rev. 0 | 26 of 116

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, 0V,

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 (−2.999954V

for a ±3.0V range at 16 bits) and the last code transition (011 …

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

full-scale input (+2.999863V for a ±3.0V range at 16 bits).

Signal-to-Noise Ratio (SNR)

SNR is the ratio of the RMS amplitude of an ADC full scale sine

wave to the RMS sum of all other spectral components below the

Nyquist frequency, excluding the first five harmonics and DC. The

value for SNR is expressed in decibels relative to full scale (dBFS).

Signal-to-Noise and Distortion (SINAD) Ratio

SINAD is the ratio of the RMS amplitude of an ADC full scale sine

wave to 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 value for SINAD is expressed in

decibels relative to full scale (dBFS).

Noise Spectral Density (NSD)

Noise Spectral Density shows the noise power per unit bandwidth

measured at the output of the ADC. NSD is numerically derived

from the dynamic range (DR) specification of the ADC (which is

obtained through a shorted-input test). The derivation assumes that

the noise is evenly distributed (that is, white) across the Nyquist

bandwidth (f < fS/2):

NSD (dBFSHz)=−DR (dB)−10×log10 fS2

To convert from the logarithmic dBFS/Hz to linear nV/√Hz units:

NSD (nVHz)=VFullScale,RMS×10NSD (dBFS/Hz)

×109

Note that to obtain the NSD referred to the input of the AD4884, the

value must be multiplied by the gain of the FDA.

Total Harmonic Distortion (THD)

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

harmonic components of the input signal to the RMS amplitude

of the fundamental frequency (carrier). The value for THD is ex-

pressed in decibels relative to carrier (dBc).

Spurious-Free Dynamic Range (SFDR)

SFDR is the ratio of the RMS amplitude of an ADC full scale

sine wave to the peak spurious signal amplitude (excluding input

signal harmonic components). The value of SFDR is expressed in

decibels relative to full scale (dBFS).

Phase Angle Mismatch

Phase Angle Mismatch quantifies the difference in timing or phase

response between the two channels of the device. It is measured

by applying the same sine wave to both channels while sampling

simultaneously, and calculating the phase shift between the two

reconstructed waveforms.

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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