AD7985 Analog Devices, AD7985 Datasheet - Page 12

• Manufacturer Part Number: AD7985
• Description: 16-Bit, 2.5 MSPS PulSAR 11 mW ADC in QFN
• Manufacturer: Analog Devices

Specifications of AD7985

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 2.5MSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: CSP

AD7985
TERMINOLOGY
Aperture Delay
Aperture delay is the measure of the acquisition performance
and is the time between the rising edge of the CNV input and
when the input signal is held for a conversion.
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.
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. It is mea-
sured with a signal at −60 dBFS so that it includes all noise
sources and DNL artifacts.
Effective Number of Bits (ENOB)
ENOB is a measurement of the resolution with a sine wave
input. It is expressed in bits and is related to SINAD as follows:
Effective Resolution
Effective resolution is expressed in bits and is calculated as follows:
Gain Error
The last transition (from 111 … 10 to 111 … 11) should occur
for an analog voltage 1½ LSB below the nominal full scale
(4.999886 V for the 0 V to 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.
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 22).
ENOB = (SINAD
Effective Resolution = log
dB
− 1.76)/6.02
2
(2
N
/RMS Input Noise)
Rev. A | Page 12 of 28
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 expressed
in bits and is calculated as follows:
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 below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
Signal-to-Noise-and-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.
Spurious-Free Dynamic Range (SFDR)
SFDR is the difference, in decibels (dB), between the rms
amplitude of the input signal and the peak spurious signal.
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.
Transient Response
Transient response is the time required for the ADC to accurately
acquire its input after a full-scale step function is applied.
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.
Noise-Free Code Resolution = log
2
(2
N
/Peak-to-Peak Noise)