AD524B AD [Analog Devices], AD524B Datasheet - Page 14

• Manufacturer Part Number: AD524B
• Description: Precision Instrumentation Amplifier
• Manufacturer: AD [Analog Devices]

AD524
ERROR BUDGET ANALYSIS
To illustrate how instrumentation amplifier specifications are
applied, we will now examine a typical case where an AD524 is
required to amplify the output of an unbalanced transducer.
Figure 46 shows a differential transducer, unbalanced by 100 ,
supplying a 0 to 20 mV signal to an AD524C. 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).
Error Source
Gain Error
Gain Instability
Gain Nonlinearity
Input Offset Voltage
Input Offset Voltage Drift
Output Offset Voltage*
Output Offset Voltage Drift* 25 V/ C
Bias Current-Source
Bias Current-Source
Offset Current-Source
Offset Current-Source
Offset Current-Source
Offset Current-Source
Common Mode Rejection
Noise, RTI
*Output offset voltage and output offset voltage drift are given as RTI figures.
Imbalance Error
Imbalance Drift
Imbalance Drift
5 V dc
(0.1 Hz–10 Hz)
Imbalance Error
Resistance-Error
Resistance-Drift
AD524C
Specifications Calculation
25 ppm
–
115 dB
0.3 V p-p
0.25%
0.003%
50 V, RTI
0.5 V/ C
2.0 mV
15 nA
100 pA/ C
10 nA
100 pA/ C
10 nA
100 pA/ C
350
350
Table II. Error Budget Analysis of AD524CD in Bridge Application
+10V
350
350
Figure 46. Typical Bridge Application
(25 ppm/ C)(60 C) = 1500 ppm
( 0.5 V/ C)(60 C) = 30 V
( 25 V/ C)(60 C)= 1500 V
( 15 nA)(100 ) = 1.5 V
( 100 pA/ C)(100 )(60 C) = 0.6 V
( 10 nA)(100 ) = 1 V
(100 pA/ C)(100 )(60 C) = 0.6 V
(10 nA)(175 ) = 3.5 V
(100 pA/ C)(175 )(60 C) = 1 V
115 dB = 1.8 ppm × 5 V = 8.8 V
8.8 V/20 mV = 444 ppm
0.3 V p-p/20 mV = 15 ppm
0.25% = 2500 ppm
0.003% = 30 ppm
50 V/20 mV = 2500 ppm
2.0 mV/20 mV = 1000 ppm
30 V/20 mV = 1500 ppm
1500 V/20 mV = 750 ppm
1.5 V/20 mV = 75 ppm
0.6 V/20 mV= 30 ppm
1 V/20 mV = 50 ppm
0.6 V/20 mV = 30 ppm
3.5 V/20 mV = 87.5 ppm
1 V/20 mV = 50 ppm
G = 100
RG
RG
Total Error
2
1
–14–
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 (45 ppm = 0.004%)
are significant. Furthermore, if a system has an intelligent pro-
cessor monitoring the A-to-D output, the addition of a auto-
gain/autozero cycle will remove all reducible errors and may
eliminate the requirement for initial calibration. This will also
reduce errors to 0.004%.
+V
S
AD524C
–V
S
10k
Effect on
Absolute
Accuracy
at T
2500 ppm
–
–
2500 ppm
–
1000 ppm
–
75 ppm
–
50 ppm
–
87.5 ppm
–
444 ppm
–
6656.5 ppm
A
= +25 C at T
0V TO 2V
14-BIT
ADC
F.S.
Effect on
Absolute
Accuracy
2500 ppm
1500 ppm
–
2500 ppm
1500 ppm
1000 ppm
750 ppm
75 ppm
30 ppm
50 ppm
30 ppm
87.5 ppm
50 ppm
444 ppm
–
10516.5 ppm
A
= +85 C
Effect
on
Resolution
–
–
30 ppm
–
–
–
–
–
–
–
–
–
–
–
15 ppm
45 ppm
REV. E