INA106
V
1
10Ω
10kΩ
100kΩ
E
1
–In
5
200Ω
6
Gain
Adjust
E
0
A
1
R
2
2
INA106
5
2
R
1
R
2
6
E
0
Output
3
1
V
2
10Ω
3
10kΩ
100kΩ
1
200Ω
CMR
Adjust
A
2
E
2
+In
To eliminate adjustment interactions,
first adjust gain with V
2
grounded.
E
0
= 10(1 + 2R
2
/R
1
) (E
2
– E
1
)
FIGURE 3. Difference Amplifier with Gain and CMR Adjust.
INA106
10kΩ
V
2
2
100kΩ
5
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. For these 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.
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.
A
1
, A
2
OPA37A
OPA111B
OPA128LM
R
1
(Ω)
50.5
202
202
R
2
(kΩ)
2.5
10
10
GAIN
(V/V)
1000
1000
1000
CMRR
(dB)
128
110
118
I
b
(pA)
40000
1
0.075
NOISE AT 1kHz
(nV/
√
Hz)
4
10
38
6
V
O
V
O
= –10V
2
10kΩ
100kΩ
3
1
FIGURE 6. Precision Instrumentation Amplifier.
Gain Error = 0.01% maximum
Nonlinearity = 0.001% maximum
Gain Drift = 2.ppm/°C
R
1
10kΩ
INA106
2
R
2
100kΩ
5
FIGURE 4. Precision G = –10 Inverting Amplifier.
INA106
2
R
1
10kΩ
R
2
100kΩ
5
V
1
1
R
4
100kΩ
R
3
10kΩ
6
V
0
V
0
= V
1
+ 10 V
3
V
3
3
V
IN
1
R
4
100kΩ
6
V
O
V
O
= V
IN
FIGURE 7. Precision Summing Amplifier.
INA106
10kΩ
100kΩ
±100V
Safe Input
3
R
3
10kΩ
2
This circuit follows an 11/1 divider with a gain of 11 for an overall gain of unity.
With an 11/1 divider, the input signal can exceed 100V without damage.
5
FIGURE 5. Voltage Follower with Input Protection.
V
IN
1
3
100kΩ
10kΩ
6
V
O
V
O
= 11V
IN
Gain Error =
0.01% maximum
FIGURE 8. Precision G = 11 Buffer.
6
INA106
www.ti.com
SBOS152A
TI [ TEXAS INSTRUMENTS ]
