AD7693 datasheet(14/29 Pages) AD

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Data Sheet

AD7903

Rev. A | Page 13 of 28

TERMINOLOGY

Integral Nonlinearity Error (INL)

INL 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.

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

Offset error is the difference between the ideal midscale voltage

(that is, 0 V) and the actual voltage producing the midscale

output code (that is, 0 LSB).

Offset Error Match

It is the difference in offsets, expressed in millivolts between the

channels of a multichannel converter. It is computed with the

following equation:

Offset Matching = VOFFSETMAX − VOFFSETMIN

where:

VOFFSETMAX is the most positive offset error.

VOFFSETMIN is the most negative offset error.

Offset matching is usually expressed in millivolts with the full-

scale input range stated in the product data sheet.

Gain Error

The first transition (from 100 … 00 to 100 … 01) should occur

at a level ½ LSB above nominal negative full scale (−4.999981 V

for the ±5 V range). The last transition (from 011 … 10 to

011 … 11) occurs for an analog voltage that is 1½ LSB below the

nominal full scale (4.999943 V for the ±5 V range). 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 Match

It is the ratio of the maximum full scale to the minimum full

scale of a multichannel ADC. It is expressed as a percentage of

full scale using the following equation:

100

























MIN

MAX

MIN

MAX

FSR

Matching

Gain

where:

FSRMAX is the most positive gain error of the ADC.

FSRMIN is the most negative gain error.

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 SINAD by the following formula:

ENOB = (SINADdB − 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. It is calculated

as follows:

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

Noise free code resolution is expressed in bits.

Effective Resolution

Effective resolution is calculated as follows:

Effective Resolution = log2(2N/RMS Input Noise)

Effective resolution 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 (dB).

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 decibels (dB). It 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 decibels (dB).

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

SINAD 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

SINAD is expressed in decibels (dB).

Aperture Delay

Aperture delay is the measure of the acquisition performance. It

is the time between the rising edge of the CNVx input and

when the input signal is held for a conversion.

Transient Response

Transient response is the time required for the ADC to accurately

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

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