Datasheet AD7690 (Analog Devices) - 9

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AD7690 Data Sheet TERMINOLOGY Integral Nonlinearity Error (INL)
and is expressed in bits. INL refers to the deviation of each individual code from a line
Effective Resolution
drawn from negative full scale through positive full scale. The Effective resolution is calculated as point used as negative full scale occurs ½ LSB before the first Effective Resolution = log2(2N/RMS Input Noise) code transition. Positive full scale is defined as a level 1½ LSB beyond the last code transition. The deviation is measured from and is expressed in bits. the middle of each code to the true straight line (see Figure 25).
Total Harmonic Distortion (THD) Differential Nonlinearity Error (DNL)
THD is the ratio of the rms sum of the first five harmonic In an ideal ADC, code transitions are 1 LSB apart. DNL is the components to the rms value of a full-scale input signal and is maximum deviation from this ideal value. It is often specified in expressed in decibels. terms of resolution for which no missing codes are guaranteed.
Dynamic Range Zero Error
Dynamic range is the ratio of the rms value of the ful scale to Zero error is the difference between the ideal midscale voltage, the total rms noise measured with the inputs shorted together. that is, 0 V, from the actual voltage producing the midscale The value for dynamic range is expressed in decibels. output code, that is, 0 LSB.
Signal-to-Noise Ratio (SNR) Gain Error
SNR is the ratio of the rms value of the actual input signal to the The first transition (from 100 .. 00 to 100 .. 01) should occur at rms sum of all other spectral components that is less than the a level ½ LSB above nominal negative ful scale (−4.999981 V Nyquist frequency, excluding harmonics and dc. The value of for the ±5 V range). The last transition (from 011 … 10 to SNR is expressed in decibels. 011 … 11) should occur for an analog voltage 1½ LSB below the
Signal-to-(Noise + Distortion) Ratio (SINAD)
nominal full scale (+4.999943 V for the ±5 V range). The gain SINAD is the ratio of the rms value of the actual input signal to error is the deviation of the difference between the actual level the rms sum of all other spectral components below the Nyquist of the last transition and the actual level of the first transition frequency, including harmonics but excluding dc. The value for from the difference between the ideal levels. SINAD is expressed in decibels.
Spurious-Free Dynamic Range (SFDR) Aperture Delay
SFDR is the difference, in decibels, between the rms amplitude Aperture delay is the measure of the acquisition performance. It of the input signal and the peak spurious signal. is the time between the rising edge of the CNV input and when
Effective Number of Bits (ENOB)
the input signal is held for a conversion. ENOB is a measurement of the resolution with a sine wave
Transient Response
input. It is related to SINAD by the fol owing formula: Transient response is the time required for the ADC to accurately ENOB = (SINAD acquire its input after a ful -scale step function is applied. dB − 1.76)/6.02 and 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: Noise-Free Code Resolution = log2(2N/Peak-to-Peak Noise) Rev. C | Page 8 of 24 Document Outline FEATURES APPLICATIONS APPLICATION EXAMPLE GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS TERMINOLOGY TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION CIRCUIT INFORMATION CONVERTER OPERATION Transfer Functions TYPICAL CONNECTION DIAGRAM ANALOG INPUTS DRIVER AMPLIFIER CHOICE SINGLE-TO-DIFFERENTIAL DRIVER VOLTAGE REFERENCE INPUT POWER SUPPLY SUPPLYING THE ADC FROM THE REFERENCE DIGITAL INTERFACE CS MODE, 3-WIRE WITHOUT BUSY INDICATOR CS MODE, 3-WIRE WITH BUSY INDICATOR CS MODE, 4-WIRE WITHOUT BUSY INDICATOR CS MODE, 4-WIRE WITH BUSY INDICATOR CHAIN MODE WITHOUT BUSY INDICATOR CHAIN MODE WITH BUSY INDICATOR APPLICATION HINTS LAYOUT EVALUATING THE AD7690 PERFORMANCE OUTLINE DIMENSIONS ORDERING GUIDE