Datasheet AD7988-1, AD7988-5 (Analog Devices) - 9

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Data Sheet AD7988-1/AD7988-5 TERMINOLOGY Integral Nonlinearity Error (INL) Effective Resolution
Effective resolution is calculated as INL refers to the deviation of each individual code from a line drawn from negative full scale through positive full scale. The Effective Resolution = log2(2N/RMS Input Noise) point used as negative full scale occurs ½ LSB before the first and is expressed in bits. code transition. Positive full scale is defined as a level 1½ LSB
Total Harmonic Distortion (THD)
beyond the last code transition. The deviation is measured from THD is the ratio of the rms sum of the first five harmonic the middle of each code to the true straight line (see Figure 30). 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
Dynamic Range
maximum deviation from this ideal value. It is often specified in Dynamic range is the ratio of the rms value of the ful scale to terms of resolution for which no missing codes are guaranteed. the total rms noise measured with the inputs shorted together.
Offset Error
The value for dynamic range is expressed in dB. It is measured The first transition should occur at a level ½ LSB above analog with a signal at −60 dBFS to include all noise sources and DNL ground (38.1 µV for the 0 V to 5 V range). The offset error is artifacts. the deviation of the actual transition from that point.
Signal-to-Noise Ratio (SNR) Gain Error
SNR is the ratio of the rms value of the actual input signal to the The last transition (from 111 … 10 to 111 … 11) should rms sum of all other spectral components below the Nyquist occur for an analog voltage 1½ LSB below the nominal full frequency, excluding harmonics and dc. The value for SNR is scale (4.999886 V for the 0 V to 5 V range). The gain error is expressed in dB. the deviation of the actual level of the last transition from the
Signal-to-(Noise + Distortion) Ratio (SINAD)
ideal level after the offset is adjusted out. SINAD is the ratio of the rms value of the actual input signal to
Spurious-Free Dynamic Range (SFDR)
the rms sum of all other spectral components below the Nyquist SFDR is the difference, in decibels (dB), between the rms frequency, including harmonics but excluding dc. The value for amplitude of the input signal and the peak spurious signal. SINAD is expressed in dB.
Effective Number of Bits (ENOB) Aperture Delay
ENOB is a measurement of the resolution with a sine wave Aperture delay is the measure of the acquisition performance. It input. It is related to SINAD by the following formula: is the time between the rising edge of the CNV input and when the input signal is held for a conversion. ENOB = (SINADdB − 1.76)/6.02
Transient Response
and is expressed in bits. Transient response is the time required for the ADC to
Noise-Free Code Resolution
accurately acquire its input after a full-scale step function is Noise-free code resolution is the number of bits beyond which applied. it is impossible to distinctly resolve individual codes. It is calculated as Noise-Free Code Resolution = log2(2N/Peak-to-Peak Noise) and is expressed in bits. Rev. F | Page 9 of 23 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION TYPICAL APPLICATION CIRCUIT 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 VOLTAGE REFERENCE INPUT POWER SUPPLY DIGITAL INTERFACE MODE, 3-WIRE MODE 4-WIRE CHAIN MODE APPLICATIONS INFORMATION INTERFACING TO BLACKFIN® DSP LAYOUT EVALUATING THE PERFORMANCE OF THE AD7988-1/AD7988-5 OUTLINE DIMENSIONS ORDERING GUIDE