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AD7982 Datasheet(HTML) 8 Page - Analog Devices

 8 / 16 pageAD7684Rev. A | Page 8 of 16TERMINOLOGYIntegral Nonlinearity Error (INL)Linearity error refers to the deviation of each individual codefrom a line drawn from negative full scale through positive fullscale. The point used as negative full scale occurs ½ LSB beforethe first code transition. Positive full scale is defined as a level1½ LSB beyond the last code transition. The deviation ismeasured from the middle of each code to the true straight line(see Figure 21).Differential Nonlinearity Error (DNL)In an ideal ADC, code transitions are 1 LSB apart. DNL is themaximum deviation from this ideal value. It is often specified interms of resolution for which no missing codes are guaranteed.Zero ErrorZero error is the difference between the ideal midscale voltage,that is, 0 V, and the actual voltage producing the midscaleoutput code, that is, 0 LSB.Gain ErrorThe first transition (from 100 . . . 00 to 100 . . . 01) shouldoccur at a level ½ LSB above the nominal negative full scale(−4.999924 V for the ±5 V range). The last transition (from011…10 to 011…11) should occur for an analog voltage1½ LSB below the nominal full scale (4.999771 V for the ±5 Vrange). The gain error is the deviation of the difference betweenthe actual level of the last transition and the actual level of thefirst transition from the difference between the ideal levels.Spurious-Free Dynamic Range (SFDR)SFDR is the difference, in decibels (dB), between the rmsamplitude of the input signal and the peak spurious signal.Effective Number of Bits (ENOB)ENOB is a measurement of the resolution with a sine waveinput. It is related to SINAD by the following formulaENOB = (SINADdB − 1.76)/6.02and is expressed in bits.Total Harmonic Distortion (THD)THD is the ratio of the rms sum of the first five harmoniccomponents to the rms value of a full-scale input signal and isexpressed in dB.Signal-to-Noise Ratio (SNR)SNR is the ratio of the rms value of the actual input signal to therms sum of all other spectral components below the Nyquistfrequency, excluding harmonics and dc. The value for SNR isexpressed in dB.Signal-to-(Noise + Distortion) Ratio (SINAD)SINAD is the ratio of the rms value of the actual input signal tothe rms sum of all other spectral components below the Nyquistfrequency, including harmonics but excluding dc. The value forSINAD is expressed in dB.Aperture DelayAperture delay is a measure of the acquisition performance andis the time between the falling edge of the CS input and whenthe input signal is held for a conversion.Transient ResponseTransient response is the time required for the ADC to accuratelyacquire its input after a full-scale step function is applied.