Datasheet

®
INA105
6
FIGURE 2. Offset Adjustment.
FIGURE 3. Precision Difference Amplifier.
For low source impedance applications, an input stage using OPA27 op
amps will give the best low noise, offset, and temperature drift performance.
At source impedances above about 10kΩ, the bias current noise of the
OPA27 reacting with the input impedance begins to dominate the noise
performance. For these applications, using the OPA111 or dual OPA2111
FET input op amp will provide lower noise performance. For lower cost use
the OPA121 plastic. To construct an electrometer use the OPA128.
R
1
R
2
GAIN CMRR MAX NOISE AT 1kHz
A
1
, A
2
(Ω)(Ω) (V/V) (dB) I
B
(nV/√HZ)
OPA27A 50.5 2.5k 100 128 40nA 4
OPA111B 202 10k 100 110 1pA 10
OPA128LM 202 10k 100 118 75fA 38
FIGURE 4. Precision Instrumentation Amplifier.
5
6
3
INA105
2
V
1
1
V
0
0utput
A
2
A
1
R
2
R
2
R
1
–In
V
1
+In
V
O
= (1 + 2R
2
/R
1
) (V
2
–V
1
)
FIGURE 5. Current Receiver with Compliance to Rails.
V
3
5
6
3
V
O
INA105
V
O
= V
3
– V
3
Offset Adjustment
Range = ±300µV
2
R
3
R
1
R
2
R
4
V
2
10
Ω
499k
Ω
10
Ω
100k
Ω
+15V
–15V
1
V
3
5
6
3
V
0
INA105BM
V
0
= V
3
– V
2
Gain Error = 0.005%
CMR = 100dB
Nonlinearity = 0.0002%
2
R
3
R
1
R
2
V
2
25k
Ω
+In
–In
25k
Ω
R
4
25k
Ω
25k
Ω
1
V–
5
6
3
INA105
2
100
1%
Ω
1
V
0
0 to 2V
I
IN
0 to 20mA
100
1%
Ω