Datasheet AD7685 (Analog Devices) - 10

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Data Sheet AD7685 TERMINOLOGY Integral Nonlinearity Error (INL) Effective Number of Bits (ENOB)
INL 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 SINAD by point used as negative full scale occurs ½ LSB before the first ENOB = (SINADdB − 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 (see Figure 26).
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.
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the actual input signal to the
Offset Error
rms sum of all other spectral components below the Nyquist The first transition should occur at a level ½ LSB above analog frequency, excluding harmonics and dc. The value for SNR is ground (38.1 µV for the 0 V to 5 V range). The offset error is expressed in dB. the deviation of the actual transition from that point.
Signal-to-(Noise + Distortion), SINAD Gain Error
SINAD is the ratio of the rms value of the actual input signal to The last transition (from 111 . 10 to 111 . 11) should the rms sum of all other spectral components below the Nyquist occur for an analog voltage 1½ LSB below the nominal full frequency, including harmonics but excluding dc. The value for scale (4.999886 V for the 0 V to 5 V range). The gain error is the SINAD is expressed in dB. deviation of the actual level of the last transition from the ideal level after the offset is adjusted out.
Aperture Delay
Aperture delay is a measure of the acquisition performance and
Spurious-Free Dynamic Range (SFDR)
is the time between the rising edge of the CNV input and when The difference, in decibels (dB), between the rms amplitude of the input signal is held for a conversion. the input signal and the peak spurious signal.
Transient Response
The time required for the ADC to accurately acquire its input after a ful -scale step function is applied. Rev. D | Page 9 of 28 Document Outline Features Applications Typical Application Circuit General Description Table of Contents Revision History Specifications Timing Specifications Absolute Maximum Ratings ESD Caution Pin Configuration 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 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-Wire, 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 Performance of the AD7685 True 16-Bit Isolated Application Example Outline Dimensions Ordering Guide