AD4697 datasheet(25/107 Pages) AD

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Data Sheet

AD4697/AD4698

TERMINOLOGY

analog.com

Rev. 0 | 25 of 107

Integral Nonlinearity Error (INL)

INL is the maximum deviation from a straight line passing through

the endpoints of the ADC transfer function. The endpoints of the

transfer function are zero scale, a point ½ LSB below the first

code transition, and full scale, a point ½ LSB above the last code

transition.

Differential Nonlinearity Error (DNL)

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

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

terms of resolution for which no missing codes are guaranteed.

Offset Error

The offset error is the deviation of the measured transition between

−FSR and −FSR + 1 from the ideal transition, measured in volts.

The ideal transition between −FSR and −FSR + 1 occurs at an

analog input level ½ LSB above the IN− voltage (see the Transfer

Function section).

Offset Error Match

Offset error match is the difference in offset error between any two

input channels.

Gain Error

The gain error is the deviation of the measured transition between

+FSR − 1 and +FSR from the ideal transition, and is measured in

percentage of full scale (%FS). The ideal transition between +FSR

− 1 and +FSR occurs for an analog input level 1½ LSB below the

nominal full scale (see the Transfer Function section).

Gain Error Match

Gain error match is the difference in gain error between any two

input channels.

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

and is related to SINAD by the following formula:

ENOB = (SINAD − 1.76)/6.02

ENOB 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. To calculate the

resolution, use the following equation:

Noise Free Code Resolution = log2 (2N/Peak-to Peak-Noise)

Noise free code resolution is expressed in bits.

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 dB and is measured with a

signal at −60 dBFS to include 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 dB.

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

SINAD is the measured ratio of signal-to-noise-and-distortion at

the output of the ADC. The signal is the rms amplitude of the

fundamental. Noise is the sum of all nonfundamental signals up to

half the sampling frequency (fS/2), excluding dc.

Channel to Channel Memory

Channel to channel memory is a measure of the level of cross-

talk that occurs when switching between channels in a channel

sequence. It is measured by applying a full-scale, 100 kHz signal

to one analog input channel and a dc voltage on another analog

input channel, and repeatedly switching between the two channels

between each conversion. The channel to channel memory is the

magnitude at 100 kHz in the spectrum measured from the dc

channel data.

Channel to Channel Isolation

Channel to channel isolation is a measure of the level of crosstalk

from a signal on an inactive channel to an active channel. To

measure channel to channel isolation, apply a dc input to one

analog input channel and a full-scale, 100 kHz sine wave signal to

all other analog input channels and perform conversions only on the

dc input channel. The channel to channel isolation is the magnitude

at 100 kHz in the spectrum measured from the dc channel data.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of harmonics to the fundamental

and is defined as

THDdB =20log V22+V32+V42+V52+V62

(1)

where:

V1 is the rms amplitude of the fundamental.

V2, V3, V4, V5, and V6 are the rms amplitudes of the second through

the sixth harmonic.

Aperture Delay

Aperture delay is the measure of the acquisition performance.

Aperture delay is the time between the rising edge of the CNV input

and when the input signal is held for a conversion.

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