AD624 查看數據表（PDF） - Analog Devices
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AD624 Datasheet PDF : 17 Pages
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AD624
ERROR BUDGET ANALYSIS
To illustrate how instrumentation amplifier specifications are
applied, we will now examine a typical case where an AD624 is
required to amplify the output of an unbalanced transducer.
Figure 47 shows a differential transducer, unbalanced by ≈5 Ω,
supplying a 0 to 20 mV signal to an AD624C. The output of the
IA feeds a 14-bit A to D converter with a 0 to 2 volt input volt-
age range. The operating temperature range is –25°C to +85°C.
Therefore, the largest change in temperature ∆T within the
operating range is from ambient to +85°C (85°C – 25°C =
60°C.)
In many applications, differential linearity and resolution are of
prime importance. This would be so in cases where the absolute
value of a variable is less important than changes in value. In
these applications, only the irreducible errors (20 ppm =
0.002%) are significant. Furthermore, if a system has an intelli-
gent processor monitoring the A to D output, the addition of an
autogain/autozero cycle will remove all reducible errors and may
eliminate the requirement for initial calibration. This will also
reduce errors to 0.002%.
+10V
350⍀
350⍀
350⍀
350⍀
RG1
G = 100
RG2
+VS
10k⍀
AD624C
–VS
14-BIT
ADC
0 TO 2V
F.S.
Figure 47. Typical Bridge Application
Table II. Error Budget Analysis of AD624CD in Bridge Application
Error Source
Gain Error
Gain Instability
Gain Nonlinearity
Input Offset Voltage
Input Offset Voltage Drift
Output Offset Voltage1
Output Offset Voltage Drift1
Bias Current–Source
Imbalance Error
Offset Current–Source
Imbalance Error
Offset Current–Source
Resistance Error
Offset Current–Source
Resistance–Drift
Common-Mode Rejection
5 V dc
Noise, RTI
(0.1 Hz–10 Hz)
AD624C
Specifications
± 0.1%
10 ppm
± 0.001%
± 25 µV, RTI
± 0.25 µV/°C
± 2.0 mV
± 10 µV/°C
± 15 nA
± 10 nA
± 10 nA
± 100 pA/°C
115 dB
0.22 µV p-p
Calculation
Effect on
Absolute
Accuracy
at TA = +25؇C
± 0.1% = 1000 ppm
(10 ppm/°C) (60°C) = 600 ppm
± 0.001% = 10 ppm
± 25 µV/20 mV = ± 1250 ppm
(± 0.25 µV/°C) (60°C)= 15 µV
15 µV/20 mV = 750 ppm
± 2.0 mV/20 mV = 1000 ppm
(± 10 µV/°C) (60°C) = 600 µV
600 µV/20 mV = 300 ppm
(± 15 nA)(5 Ω ) = 0.075 µV
0.075 µV/20mV = 3.75 ppm
(± 10 nA)(5 Ω) = 0.050 µV
0.050 µV/20 mV = 2.5 ppm
(10 nA) (175 Ω) = 1.75 µV
1.75 µV/20 mV = 87.5 ppm
(100 pA/°C) (175 Ω) (60°C) = 1 µV
1 µV/20 mV = 50 ppm
115 dB = 1.8 ppm × 5 V = 9 µV
9 µV/20 mV = 444 ppm
1000 ppm
_
–
1250 ppm
–
1000 ppm
–
3.75 ppm
2.5 ppm
87.5 ppm
–
450 ppm
0.22 µV p-p/20 mV = 10 ppm
_
Effect on
Absolute
Accuracy
at TA = +85؇C
Effect
on
Resolution
1000 ppm
600 ppm
–
1250 ppm
–
–
10 ppm
–
750 ppm
–
1000 ppm
–
300 ppm
–
3.75 ppm
–
2.5 ppm
–
87.5 ppm
–
50 ppm
–
450 ppm
–
–
10 ppm
Total Error
3793.75 ppm 5493.75 ppm 20 ppm
NOTE
1Output offset voltage and output offset voltage drift are given as RTI figures.
For a comprehensive study of instrumentation amplifier design
and applications, refer to the Instrumentation Amplifier Application
Guide, available free from Analog Devices.
–14–
REV. C
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