Datasheet AD7684 (Analog Devices) - 9

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AD7684 TERMINOLOGY Integral Nonlinearity Error (INL) Effective Number of Bits (ENOB)
Linearity error refers to the deviation of each individual code ENOB is a measurement of the resolution with a sine wave from a line drawn from negative full scale through positive full input. It is related to SINAD by the following formula scale. The point used as negative full scale occurs ½ LSB before ENOB = (SINADdB − 1.76)/6.02 the first code transition. Positive full scale is defined as a level and is expressed in bits. 1½ LSB beyond the last code transition. The deviation is measured from the middle of each code to the true straight line
Total Harmonic Distortion (THD)
(see Figure 21). 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
Differential Nonlinearity Error (DNL)
expressed in dB. In an ideal ADC, code transitions are 1 LSB apart. DNL is the maximum deviation from this ideal value. It is often specified in
Signal-to-Noise Ratio (SNR)
terms of resolution for which no missing codes are guaranteed. 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
Zero Error
frequency, excluding harmonics and dc. The value for SNR is Zero error is the difference between the ideal midscale voltage, expressed in dB. that is, 0 V, and the actual voltage producing the midscale output code, that is, 0 LSB.
Signal-to-(Noise + Distortion) Ratio (SINAD)
SINAD is the ratio of the rms value of the actual input signal to
Gain Error
the rms sum of all other spectral components below the Nyquist The first transition (from 100 . 00 to 100 . 01) should frequency, including harmonics but excluding dc. The value for occur at a level ½ LSB above the nominal negative full scale SINAD is expressed in dB. (−4.999924 V for the ±5 V range). The last transition (from 011…10 to 011…11) should occur for an analog voltage
Aperture Delay
1½ LSB below the nominal full scale (4.999771 V for the ±5 V Aperture delay is a measure of the acquisition performance and range). The gain error is the deviation of the difference between is the time between the falling edge of the CS input and when the actual level of the last transition and the actual level of the the input signal is held for a conversion. first transition from the difference between the ideal levels.
Transient Response Spurious-Free Dynamic Range (SFDR)
Transient response is the time required for the ADC to accurately SFDR is the difference, in decibels (dB), between the rms acquire its input after a full-scale step function is applied. amplitude of the input signal and the peak spurious signal. Rev. A | Page 8 of 16 Document Outline FEATURES APPLICATIONS APPLICATION DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING SPECIFICATIONS Timing Diagrams ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TERMINOLOGY TYPICAL PERFORMANCE CHARACTERISTICS APPLICATION INFORMATION CIRCUIT INFORMATION CONVERTER OPERATION TRANSFER FUNCTIONS TYPICAL CONNECTION DIAGRAM ANALOG INPUTS DRIVER AMPLIFIER CHOICE VOLTAGE REFERENCE INPUT POWER SUPPLY DIGITAL INTERFACE LAYOUT EVALUATING THE PERFORMANCE OF THE AD7684 OUTLINE DIMENSIONS ORDERING GUIDE