AD7634 Analog Devices, AD7634 Datasheet - Page 16

• Manufacturer Part Number: AD7634
• Manufacturer: Analog Devices

Specifications of AD7634

• Resolution (bits): 18bit
• # Chan: 1
• Sample Rate: 670kSPS
• Interface: Byte,Par,Ser,SPI
• Analog Input Type: Diff-Bip,Diff-Uni
• Ain Range: 10V p-p,20 V p-p,40 V p-p
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

AD7634
TERMINOLOGY
Least Significant Bit (LSB)
The least significant bit, or LSB, is the smallest increment that
can be represented by a converter. For a fully differential input
ADC with N bits of resolution, the LSB expressed in volts is
Integral Nonlinearity Error (INL)
Linearity error 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 a ½ LSB before
the first code transition. Positive full scale is defined as a level
1½ LSBs beyond the last code transition. The deviation is meas-
ured from the middle of each code to the true straight line.
Differential Nonlinearity Error (DNL)
In an ideal ADC, code transitions are 1 LSB apart. Differential
nonlinearity is the maximum deviation from this ideal value. It
is often specified in terms of resolution for which no missing
codes are guaranteed.
Bipolar Zero Error
The difference between the ideal midscale input voltage (0 V)
and the actual voltage producing the midscale output code.
Unipolar Offset Error
The first transition should occur at a level ½ LSB above analog
ground. The unipolar offset error is the deviation of the actual
transition from that point.
Full-Scale Error
The last transition (from 111…10 to 111…11 in straight binary
format) should occur for an analog voltage 1½ LSB below the
nominal full-scale. The full-scale error is the deviation in LSB
(or % of full-scale range) of the actual level of the last transition
from the ideal level and includes the effect of the offset error.
Closely related is the gain error (also in LSB or % of full-scale
range), which does not include the effects of the offset error.
Dynamic Range
Dynamic range is the ratio of the rms value of the full scale to
the rms noise measured for an input typically at −60 dB. 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 below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
LSB
(
V
)
=
V
2
INp-p
N
Rev. A | Page 16 of 32
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.
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.
Spurious-Free Dynamic Range (SFDR)
The difference, in decibels (dB), 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 and is expressed in bits by
Aperture Delay
Aperture delay is a measure of the acquisition performance
measured from the falling edge of the CNVST input to when
the input signal is held for a conversion.
Transient Response
The time required for the AD7634 to achieve its rated accuracy
after a full-scale step function is applied to its input.
Reference Voltage Temperature Coefficient
Reference voltage temperature coefficient is derived from the
typical shift of output voltage at 25°C on a sample of parts at
the maximum and minimum reference output voltage (V
measured at T
where:
V
V
V
T
T
MAX
MIN
REF
REF
REF
ENOB = [(SINAD
(Max) = maximum V
(Min) = minimum V
(25°C) = V
= –40°C.
TCV
= +85°C.
REF
(
ppm/
MIN
REF
, T(25°C), and T
°
at 25°C.
C
)
dB
=
V
− 1.76)/6.02]
REF
REF
REF
V
REF
at T
(
at T
25
(
MAX
Max
°
MIN
MIN
C
. It is expressed in ppm/°C as
)
, T(25°C), or T
, T(25°C), or T
– )
×
T (
V
REF
MAX
(
–
Min
T
MIN
)
MAX
)
MAX
×
10
.
.
6
REF
)