Datasheet AD7665 (Analog Devices) - 9

AD7665 DEFINITION OF SPECIFICATIONS Effective Number of Bits (ENOB) Internal Nonlinearity Error (INL)
A measurement of the resolution with a sine wave input. It is Linearity error refers to the deviation of each individual code related to S/(N+D) by the following formula: from a line drawn from “negative full scale” through “positive full scale.” The point used as negative full scale occurs 1/2 LSB ENOB = S N ( [ + D] -1 7. )6 6 0. )2 dB before the first code transition. Positive full scale is defined as a level 1 1/2 LSB beyond the last code transition. The deviation is and is expressed in bits. measured from the middle of each code to the true straight line.
Total Harmonic Distortion (THD) Differential Nonlinearity Error (DNL)
The rms sum of the first five harmonic components to the rms In an ideal ADC, code transitions are 1 LSB apart. Differential value of a full-scale input signal, expressed in decibels. nonlinearity is the maximum deviation from this ideal value. It is
Signal-To-Noise Ratio (SNR)
often specified in terms of resolution for which no missing codes The ratio of the rms value of the actual input signal to the are guaranteed. rms sum of all other spectral components below the Nyquist
Full-Scale Error
frequency, excluding harmonics and dc. The value for SNR is The last transition (from 011 . 10 to 011 . 11 in twos expressed in decibels. complement coding) should occur for an analog voltage 1 1/2 LSB
Signal To (Noise + Distortion) Ratio (S/[N+D])
below the nominal full scale (2.499886 V for the ±2.5 V range). The ratio of the rms value of the actual input signal to the rms sum The full-scale error is the deviation of the actual level of the last of all other spectral components below the Nyquist frequency, transition from the ideal level. including harmonics but excluding dc. The value for S/(N+D) is
Bipolar Zero Error
expressed in decibels. The difference between the ideal midscale input voltage (0 V) and
Aperture Delay
the actual voltage producing the midscale output code. A measure of the acquisition performance measured from the
Unipolar Zero Error
falling edge of the CNVST input to when the input signal is In Unipolar Mode, the first transition should occur at a level held for a conversion. 1/2 LSB above analog ground. The unipolar zero error is the
Transient Response
deviation of the actual transition from that point. The time required for the AD7665 to achieve its rated accuracy
Spurious-Free Dynamic Range (SFDR)
after a full-scale step function is applied to its input. The difference, in decibels (dB), between the rms amplitude of the input signal and the peak spurious signal. –8– REV. C