AD7652AST datasheet(11/28 Pages) AD

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AD7652

Rev. 0 | Page 11 of 28

DEFINITIONS OF SPECIFICATIONS

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 LSB 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.

Full-Scale Error

The last transition (from 011…10 to 011…11 in twos

complement coding) should occur for an analog voltage 1½ LSB

below the nominal full scale (2.49994278 V for the 0 V to 2.5 V

range). The full-scale error is the deviation of the actual level of

the last transition from the ideal level.

Unipolar Zero Error

The first transition should occur at a level ½ LSB above analog

ground (19.073 µV for the 0 V to 2.5 V range). Unipolar zero

error is the deviation of the actual transition from that point.

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 S/(N+D) by the following formula:

ENOB = (S/[N+D]dB – 1.76)/6.02

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.

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 + Distortion) Ratio (S/[N+D])

S/(N+D) 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 S/(N+D) is expressed in decibels.

Aperture Delay

Aperture delay is a measure of the acquisition performance and

is measured from the falling edge of the CNVST input to when

the input signal is held for a conversion.

Transient Response

Transient response is the time required for the AD7652 to

achieve its rated accuracy after a full-scale step function is

applied to its input.

Overvoltage Recovery

Overvoltage recovery is the time required for the ADC to

recover to full accuracy after an analog input signal 150% of the

full-scale value is reduced to 50% of the full-scale value.

Reference Voltage Temperature Coefficient

Reference voltage temperature coefficient is the change of

internal reference voltage output voltage V over the operating

temperature range and normalized by the output voltage at

25°C, expressed in ppm/°C. The equation follows:

)

–

(

)

(

)

(

–

)

(

)

(

ppm

TCV

where:

V(25°C) = V at +25°C

V(T2) = V at Temperature 2 (+85°C)

V(T1) = V at Temperature 1 (–40°C)

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