INA106
E1
–In
A1
INA106
10Ω
10kΩ
100kΩ
V1
2
5
6
1
R2
2
5
6
1
Gain
Adjust
200Ω
E0
R1
E0
Output
R2
10Ω
10kΩ
100kΩ
V2
3
3
CMR
Adjust
200Ω
A2
E0 = 10(1 + 2R2 /R1) (E2 – E1)
To eliminate adjustment interactions,
first adjust gain with V2 grounded.
E2
+In
FIGURE3. DifferenceAmplifierwithGainandCMRAdjust.
To make a high performance high gain instrumentation amplifier, the INA106
can be combined with state-of-the-art op amps. For low source impedance
applications, OPA37s will give the best noise, offset, and temperature drift. At
source impedances above about 10kΩ, the bias current noise of the OPA37
reacting with input impedance degrades noise. Forthese applications, use an
OPA111 or a dual OPA2111 FET input op amp for lower noise. For an
electrometer grade IA, use the OPA128—see table below.
INA106
10kΩ
100kΩ
2
5
6
Using the INA106 for the difference amplifier also extends the input common-
mode range of the instrumentation amplifier to ±10V. A conventional IA with
a unity-gain difference amplifier has an input common-mode range limited to
±5V for an output swing of ±10V. This is because a unity-gain difference amp
needs ±5V at the input for 10V at the output, allowing only 5V additional for
common-mode.
V2
VO
VO = –10V2
R1
R2
GAIN CMRR
NOISE AT 1kHz
A1, A2
(Ω) (kΩ) (V/V)
(dB)
Ib (pA)
(nV/ √Hz)
10kΩ
100kΩ
OPA37A
OPA111B
OPA128LM
50.5 2.5
1000
1000
1000
128
110
118
40000
1
0.075
4
10
38
202
202
10
10
3
1
FIGURE 6. Precision Instrumentation Amplifier.
Gain Error = 0.01% maximum
Nonlinearity = 0.001% maximum
Gain Drift = 2.ppm/°C
INA106
R1
R2
10kΩ
100kΩ
FIGURE 4. Precision G = –10 Inverting Amplifier.
2
5
6
R4
100kΩ
V0
INA106
V1
V3
1
3
R1
R2
V0 = V1 + 10 V3
10kΩ
100kΩ
2
1
5
6
R3
10kΩ
R4
100kΩ
VO
VIN
FIGURE 7. Precision Summing Amplifier.
V
O = VIN
±100V
Safe Input
R3
10kΩ
INA106
3
10kΩ
100kΩ
2
5
6
Thiscircuitfollowsan11/1dividerwithagainof11foranoverallgainofunity.
With an 11/1 divider, the input signal can exceed 100V without damage.
VO
100kΩ
10kΩ
FIGURE 5. Voltage Follower with Input Protection.
1
3
VO = 11VIN
VIN
Gain Error =
0.01% maximum
FIGURE 8. Precision G = 11 Buffer.
INA106
6
SBOS152A
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