2
1–
1
1
+
1
β
A
VOL
1
+
R
F
1–
1
+
β
A
VOL
β
= Feedback Factor
A
VOL
= Open Loop Gain at Signal Frequency
V
OS
= Input Offset Voltage
I
= Input Bias Current
PSR = Power Supply Rejection (
μ
V/V) [Assuming a 20% change with
±
15V supplies. Total error is twice that due to one supply.]
1–
1
1
+
1
10
6
/ 200
1
200
1
200
1
200
1
200
500VDC
140dB
1
200
[
[
0.75
100
0.25
100
]
]
]
]
V
E(ISO)
=
1
200
V
ISO
IMR
+
V
OS
+
GE
+
Nonlinearity
+
PSR
+
Noise
0.025mV 1
+
1
200
40 x 10
–9
x 10
3
[
[
1
200
[
]
THE ERRORS OF THE OP AMP AT 25
°
C (Referred to Input, RTI)
V
E (OPA)
= V
D
+ V
OS
+ I
B
R
1
+ PSR + Noise
V
E (OPA)
= Total Op Amp Error (RTI)
V
D
= Differential Voltage (Full Scale) Across Shunt
= Gain Error Due to Finite Open Loop Gain
Noise = 5nV/
√
Hz (for 1k
source resistance and 1kHz bandwidth)
ERROR
(OPA)
(RTI)
GAIN ERROR
OFFSET
PSR
NOISE
V
E (OPA)
=50mV
+
+ [20
μ
V/V x 3V x 2] +
[5nV
√
120 (nVrms)]
=
0.01mV
+
[0.0251mV + 0.04mV]
+
0.12mV
+
55nVrms
Error as % of FSR
=
0.02%
+
[0.05% + 0.08%]
+
0.24%
+
0.00011%
After Nulling
=
=
0.01mV
0.13mV
+
[0mV + 0mV]
+
0.12mV
+
55nVrms
Error as % of FSR
(1)
=
=
0.02%
+
[0% + 0%]
+
0.24%
+
0.00011%
0.26% of 50mV
NOTE: (1) FSR = Full-Scale Range. 50mV at input to op amp, or 10V at input (and output) of ISO amp.
THE ERRORS OF THE ISO AMP AT 25
°
C (RTI)
V
= Total ISO Amp Error
IMR = Isolation Mode Rejection
V
OS
= Input Offset Voltage
V
ISO
= V
IMV
= Isolation Voltage = Isolation Mode Voltage
GE = Gain Error (% of FSR)
Nonlinearity = Peak-to-peak deviation of output voltage from best-fit straight line. It is expressed as ratio based on full-scale range.
PSR = Change in V
OS
/10V x Supply Change
Noise = Spectral noise density x
√
bandwidth. It is recommended that bandwidth be limited to twice maximum signal bandwidth for optimum dynamic
range.
ERROR
(ISO)
(RTI)
IMR
V
OS
GAIN ERROR
NONLINEARITY
PSR
NOISE
V
E (ISO)
=
+
70mV
+
20V X
+
+
3.7mV x 3V x 2
+ 16
μ
V
√
120 (rms)
=
0.05mV
+
70mV
+
50mV
+
15mV
+
22.2mV
+
0.175mVrms
Error as % of FSR
(1)
=
0.0005%
+
0.7%
+
0.5%
+
0.15%
+
0.22%
+
0.00175%
After Nulling
V
E (ISO)
=
0.05mV
+
0mV
+
0mV
+
15mV
+
22.2mV
+
0.175mVrms
=
37.2mV
=
0.19mV
Error as % of FSR
=
=
0.0005%
0.37% of 50mV
+
0%
+
0%
+
0.15%
+
0.22%
+
0.00175%
Total Error
=
=
=
=
V
E (OPA)
0.13mV
0.32mV
+
+
V
E (ISO)
0.19mV
0.64% of 50mV