AD4685 datasheet(13/32 Pages) AD

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Data Sheet

AD4684/AD4685

TERMINOLOGY

analog.com

Rev. 0 | 13 of 32

Differential Nonlinearity (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.

Integral Nonlinearity (INL)

INL is 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.

Gain Error

The first transition (from 000…000 to 000…001) must occur at a

level ½ LSB above nominal negative full scale. The last transition

(from 111…110 to 111…111) occurs for an analog voltage 1½ LSB

below the nominal full scale. 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.

Gain Error Temperature Drift

The gain error change due to a temperature change of 1°C.

Gain Error Match

Gain error match is the difference in negative full-scale error be-

tween the input channels and the difference in positive full-scale

error between the input channels.

Offset Error

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

ground. The offset error is the deviation of the actual transition from

that point.

Offset Error Temperature Drift

The zero error change due to a temperature change of 1°C.

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.

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.

Total Harmonic Distortion (THD)

THD is the ratio of the rms sum of the first five harmonic compo-

nents to the rms value of a full-scale input signal and is expressed

in decibels.

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

SINAD is the ratio of the rms value of the actual input signal to the

rms sum of all other spectral components that are less than the

Nyquist frequency, including harmonics but excluding dc. The value

for SINAD is expressed in decibels.

Channel to Channel Memory

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

between channels in sequencer mode. It is measured by applying a

full-scale signal of a specific frequency in one analog input channel

of the ADC and determining how much that signal is attenuated in

the alternate ADC channel, when a full-scale signal of different fre-

quency is applied. The figure given is the typical value in decibels

and is measured for both ADC A and ADC B.

Power Supply Rejection Ratio (PSRR)

Variations in power supply affect the full-scale transition but not the

linearity of the converter. Power supply rejection is the maximum

change in the full-scale transition point due to the change in the

power supply voltage from the nominal value. PSRR is the ratio of

power in the ADC output at full-scale frequency, f, to the power of a

100 mV p-p sine wave applied to the VCC supply of the ADC of the

FS frequency.

PSRR (dB) = 10log(Pf/Pfs)

where:

Pf is equal to the power at f in the ADC output.

Pfs is equal to the power at full-scale coupled onto the VCC supply.

Aperture Delay

Aperture delay is the measure of the acquisition performance and

is the time between the falling edge of the CS input and when the

input signal is held for a conversion.

Aperture Jitter

Aperture jitter is the variation in aperture delay.

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