AD7989-1/AD7989-5

Data Sheet

TERMINOLOGY

Integral Nonlinearity Error (INL)

INL refers to the deviation of each individual code from a line

drawn from negative full scale through positive full scale. The

point used as negative full scale occurs ½ LSB before the first

code transition. Positive full scale is defined as a level 1½ LSB

beyond the last code transition. The deviation is measured from

the middle of each code to the true straight line (see Figure 25).

Differential Nonlinearity Error (DNL)

In an ideal ADC, code transitions are 1 LSB apart. DNL is the

maximum deviation from this ideal value. It is often specified in

terms of resolution for which no missing codes are guaranteed.

Zero Error

Zero error is the difference between the ideal midscale voltage,

that is, 0 V, and the actual voltage producing the midscale

output code, that is, 0 LSB.

Gain Error

The first transition (from 100 … 00 to 100 …01) should occur

at a level ½ LSB above nominal negative full scale (−4.999981 V

for the ±5 V range). The last transition (from 011 … 10 to

011 … 11) occurs for an analog voltage 1½ LSB below the

nominal full scale (+4.999943 V for the ±5 V range). The gain

error is the deviation of the difference between the actual level

of the last transition and the actual level of the first transition from

the difference between the ideal levels.

Spurious-Free Dynamic Range (SFDR)

SFDR is the difference, in decibels (dB), between the rms

amplitude of the input signal and the peak spurious signal.

Effective Number of Bits (ENOB)

ENOB is a measurement of the resolution with a sine wave

input. It is related to SINAD as follows:

and is expressed in bits.

Noise-Free Code Resolution

Noise-free code resolution is the number of bits beyond which it is

impossible to distinctly resolve individual codes. It is calculated as

and is expressed in bits.

Effective Resolution

Effective resolution is calculated as

and is expressed in bits.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of the first five harmonic

components to the rms value of a full-scale input signal and is

expressed in decibels.

Dynamic Range

Dynamic range is the ratio of the rms value of the full scale to

the total rms noise measured with the inputs shorted together.

The value for dynamic range is expressed in decibels. It is

measured with a signal at −60 dB so that it includes all noise

sources and DNL artifacts.

Signal-to-Noise Ratio (SNR)

SNR is the ratio of the rms value of the actual input signal to the

rms sum of all other spectral components below the Nyquist

frequency, excluding harmonics and dc. The value for SNR is

expressed in decibels.

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

SINAD is the ratio of the rms value of the actual input signal to

the rms sum of all other spectral components that are less than

the Nyquist frequency, including harmonics but excluding dc.

The value of SINAD is expressed in decibels.

Aperture Delay

Aperture delay is the measure of the acquisition performance

and is the time between the rising edge of the CNV input and

when the input signal is held for a conversion.

Transient Response

Transient response is the time required for the ADC to accurately

acquire its input after a full-scale step function is applied.

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