
AD7641
Preliminary Technical Data
TERMINOLOGY
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 1/2 LSB 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
measured from the middle of each code to the true straight line.
Rev. Pr E | Page 10 of 24
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.
Gain Error
The first transition (from 000 . . . 00 to 000 . . . 01) should occur
for an analog voltage 1/2 LSB above the nominal – full scale
(2.047992 V for the ±2.048V range). The last transition (from
111 . . . 10 to 111 . . . 11) should occur for an analog voltage
1 LSB below the nominal full scale (2.047977 V for the
±2.048V 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.
Zero Error
The zero error is the difference between the ideal mid-scale
input voltage (0 V) and the actual voltage producing the mid-
scale output code.
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 S/(N+D) by the following formula:
(
.
/
+
=
dB
D
N
S
ENOB
[
]
)
.
)
02
76
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 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 below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
Signal to (Noise + Distortion) Ratio (S/[N+D])
S/(N+D) 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 S/(N+D) is expressed in decibels.
Aperture Delay
Aperture delay is a measure of the acquisition performance and
is 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 AD7641 to achieve its rated accuracy
after a full-scale step function is applied to its input.
Reference Voltage Temperature Coefficient
The change of the internal reference output voltage V over the
operating temperature range and normalized by the output
voltage at 25°C, expressed in ppm/°C. The equation follows:
( )
(
25
°
C
V
(
)
( )
T
)
(
×
)
6
1
2
10
/
×
=
°
T
V
V
C
ppm
TCV
where:
V(25°C) = V at 25°C
V(T
2
) = V at Temperature 2
V(T
1
) = V at Temperature 1
Reference Voltage Long-Term Stability
Typical shift of output voltage at 25°C on a sample of parts
subjected to operation life test of 1000 hours at 125°C:
( )
( )
( )
V
where:
V(t
0
) = V at 25°C at Time 0
V(t
1
) = V at 25°C after 1,000 hours operation at 125°C
Reference Voltage Thermal Hysteresis
Thermal hysteresis is defined as the change of output voltage
after the device is cycled through temperature from +25°C to -
40°C to +125°C and back to +25°C. This is a typical value from
a sample of parts put through such a cycle
(
)
6
10
×
=
V
V
ppm
V
(
)
(
°
)
(
)
6
10
25
25
C
×
°
=
V
C
V
V
ppm
V
TC
HYS
where:
V(25°C) = V at 25°C
V
TC
= V at 25°C after temperature cycle at +25°C to -40°C to
+125°C and back to +25°C