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AD7660

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DEFINITION 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 1/2 LSB

before the first code transition. “Positive full scale” is defined as a

level 1 1/2 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 two’s

complement coding) should occur for an analog voltage 1 1/2 LSB

below the nominal full scale (2.49994278 V for the 0 V–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 1/2 LSB above analog

ground (19.073

µV for the 0 V–2.5 V range). Unipolar zero error is

the deviation of the actual transition from that point.

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 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 AND 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

The time required for the AD7660 to achieve its rated accuracy

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

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