AD7690 Analog Devices, AD7690 Datasheet - Page 8

• Manufacturer Part Number: AD7690
• Manufacturer: Analog Devices

Specifications of AD7690

• Resolution (bits): 18bit
• # Chan: 1
• Sample Rate: 400kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

AD7690
TERMINOLOGY
Integral Nonlinearity Error (INL)
INL refers to the deviation of each individual code from a line
drawn from negative full scale through positive full scale. The
point used as negative full scale occurs ½ LSB before the first
code transition. Positive full scale is defined as a level 1½ LSB
beyond the last code transition. The deviation is measured from
the middle of each code to the true straight line (see Figure 25).
Differential Nonlinearity Error (DNL)
In an ideal ADC, code transitions are 1 LSB apart. DNL is the
maximum deviation from this ideal value. It is often specified in
terms of resolution for which no missing codes are guaranteed.
Zero Error
Zero error is the difference between the ideal midscale voltage,
that is, 0 V, from the actual voltage producing the midscale
output code, that is, 0 LSB.
Gain Error
The first transition (from 100 ... 00 to 100 ... 01) should occur at
a level ½ LSB above nominal negative full scale (−4.999981 V
for the ±5 V range). The last transition (from 011 … 10 to
011 … 11) should occur for an analog voltage 1½ LSB below the
nominal full scale (+4.999943 V for the ±5 V range). The gain
error is the deviation of the difference between the actual level
of the last transition and the actual level of the first transition
from the difference between the ideal levels.
Spurious-Free Dynamic Range (SFDR)
SFDR is the difference, in decibels, between the rms amplitude
of the input signal and the peak spurious signal.
Effective Number of Bits (ENOB)
ENOB is a measurement of the resolution with a sine wave
input. It is related to SINAD by the following formula:
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:
and is expressed in bits.
ENOB = (SINAD
Noise-Free Code Resolution = log
dB
− 1.76)/6.02
2
(2
N
/Peak-to-Peak Noise)
Rev. B | Page 8 of 24
Effective Resolution
Effective resolution is calculated as
and is expressed in bits.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of the first five harmonic
components to the rms value of a full-scale input signal and is
expressed in decibels.
Dynamic Range
Dynamic range is the ratio of the rms value of the full scale to
the total rms noise measured with the inputs shorted together.
The value for dynamic range is expressed in decibels.
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the actual input signal to the
rms sum of all other spectral components that is less than the
Nyquist frequency, excluding harmonics and dc. The value of
SNR is expressed in decibels.
Signal-to-(Noise + Distortion) Ratio (SINAD)
SINAD is the ratio of the rms value of the actual input signal to
the rms sum of all other spectral components below the Nyquist
frequency, including harmonics but excluding dc. The value for
SINAD is expressed in decibels.
Aperture Delay
Aperture delay is the measure of the acquisition performance. It
is the time between the rising edge of the CNV input and when
the input signal is held for a conversion.
Transient Response
Transient response is the time required for the ADC to accurately
acquire its input after a full-scale step function is applied.
Effective Resolution = log
2
(2
N
/RMS Input Noise)