AD7621 datasheet(11/32 Pages) AD

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AD7621

Rev. 0 | Page 11 of 32

TERMINOLOGY

Integral Nonlinearity Error (INL)

Linearity error 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 LSBs beyond the last code transition. The deviation is

measured from the middle of each code to the true straight line.

Differential Nonlinearity Error (DNL)

In an ideal ADC, code transitions are 1 LSB apart. Differential

nonlinearity is the maximum deviation from this ideal value. It

is often specified in terms of resolution for which no missing

codes are guaranteed.

Gain Error

The first transition (from 000…00 to 000…01) should occur for

an analog voltage ½ LSB above the nominal negative full-scale

(−2.0479688 V for the ±2.048 V range). The last transition

(from 111…10 to 111…11) should occur for an analog voltage

1½ LSBs below the nominal full-scale (2.0479531 V for the

±2.048 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.

Zero Error

The zero error is the difference between the ideal midscale

input voltage (0 V) and the actual voltage producing the

midscale output code.

Dynamic Range

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

the rms noise measured with the inputs shorted together. The

value for dynamic range is expressed in decibels.

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.

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.

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

SINAD 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, including harmonics but excluding dc. The value for

SINAD is expressed in decibels.

Spurious-Free Dynamic Range (SFDR)

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 and is expressed in bits by

ENOB = [(SINADdB − 1.76)/6.02]

Aperture Delay

Aperture delay is a measure of the acquisition performance

measured from the falling edge of the CNVST input to when

the input signal is held for a conversion.

Transient Response

The time required for the AD7621 to achieve its rated accuracy

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

Reference Voltage Temperature Coefficient

Reference voltage temperature coefficient is derived from the

typical shift of output voltage at 25°C on a sample of parts at the

maximum and minimum reference output voltage (VREF)

measured at TMIN, T(25°C), and TMAX. It is expressed in ppm/°C as

MIN

MAX

REF

)

–

(

)

(

)

(

–

)

(

)

(

TCV

ppm/

Min

Max

where:

VREF (Max) = maximum VREF at TMIN, T (25°C), or TMAX

VREF (Min) = minimum VREF at TMIN, T (25°C), or TMAX

VREF (25°C) = VREF at 25°C

TMAX = +85°C

TMIN = –40°C

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