AD7694

Rev. A | Page 8 of 16

TERMINOLOGY

Integral Nonlinearity Error (INL)

Linearity error refers to the deviation of each individual code

from a line drawn from negative full scale to 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

1 ½ LSB beyond the last code transition. The deviation is

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

(see Figure 19).

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.

Offset Error

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

ground (38.1 μV for the 0 V to 5 V range). The offset error is

the deviation of the actual transition from that point.

Gain Error

The last transition (from 111...10 to 111...11) should occur for

an analog voltage 1 ½ LSB below the nominal full scale

(4.999886 V for the 0 V to 5 V range). The gain error is the

deviation of the actual level of the last transition from the ideal

level after the offset has been adjusted out.

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

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 dB.

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 dB.

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 dB.

Aperture Delay

Aperture delay is a measure of the acquisition performance and

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

the input signal is held for conversion.

Transient Response

The time required for the ADC to accurately acquire its input

after a full-scale step function is applied.