Datasheet AD7688 (Analog Devices) - 9

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AD7688 Data Sheet TERMINOLOGY Integral Nonlinearity Error (INL) Effective Number of Bits (ENOB)
It refers to the deviation of each individual code from a line ENOB is a measurement of the resolution with a sine wave drawn from negative full scale through positive full scale. The input. It is related to S/(N+D) by the following formula point used as negative full scale occurs ½ LSB before the first ENOB = (S/[N + D]dB − 1.76)/6.02 code transition. Positive full scale is defined as a level 1½ LSB and is expressed in bits. beyond the last code transition. The deviation is measured from the middle of each code to the true straight line (Figure 25).
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of the first five harmonic
Differential Nonlinearity Error (DNL)
components to the rms value of a full-scale input signal and is In an ideal ADC, code transitions are 1 LSB apart. DNL is the expressed in dB. maximum deviation from this ideal value. It is often specified in terms of resolution for which no missing codes are guaranteed.
Dynamic Range
It is the ratio of the rms value of the full scale to the total rms
Zero Error
noise measured with the inputs shorted together. The value for It is the difference between the ideal midscale voltage, that is, 0 dynamic range is expressed in dB. V, from the actual voltage producing the midscale output code, that is, 0 LSB.
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the actual input signal to the
Gain Error
rms sum of all other spectral components below the Nyquist The first transition (from 100 . 00 to 100 . 01) should occur frequency, excluding harmonics and dc. The value for SNR is at a level ½ LSB above nominal negative full scale (−4.999924 V expressed in dB. for the ±5 V range). The last transition (from 011…10 to 011…11) should occur for an analog voltage 1½ LSB below the
Signal-to-(Noise + Distortion) Ratio (S/[N+D])
nominal full scale (+4.999771 V for the ±5 V range.) The gain S/(N+D) is the ratio of the rms value of the actual input signal error is the deviation of the difference between the actual level to the rms sum of all other spectral components below the of the last transition and the actual level of the first transition Nyquist frequency, including harmonics but excluding dc. The from the difference between the ideal levels. value for S/(N+D) is expressed in dB.
Spurious-Free Dynamic Range (SFDR) Aperture Delay
SFDR is the difference, in decibels (dB), between the rms Aperture delay is the measure of the acquisition performance. It amplitude of the input signal and the peak spurious signal. is the time between the rising edge of the CNV input and when the input signal is held for a conversion.
Transient Response
It is the time required for the ADC to accurately acquire its input after a full-scale step function was applied. Rev. B | Page 8 of 28 Document Outline Features Applications Application Diagram General Description Table of Contents Revision History Specifications Timing Specifications Absolute Maximum Ratings Thermal Resistance ESD Caution Pin Configuration and Function Descriptions Terminology Typical Performance Characteristics Circuit Information Converter Operation Transfer Functions Typical Connection Diagram Analog Input Driver Amplifier Choice Single-to-Differential Driver Voltage Reference Input Power Supply Supplying the ADC from the Reference Digital Interface /CS Mode 3-Wire, No BUSY Indicator /CS Mode 3-Wire with BUSY Indicator /CS Mode 4-Write, No BUSY Indicator /CS Mode 4-Wire with BUSY Indicator Chain Mode, No BUSY Indicator Chain Mode with BUSY Indicator Application Hints Layout Evaluating the AD7688 Performance Outline Dimensions Ordering Guide