negative input exceeds that in the positive input, stray
capacitance from the output will create a net negative feed-
back and improve the circuit stability. If the impedance in
the positive input is greater, the feedback due to stray
capacitance will be positive and instability may result. The
degree of positive feedback depends upon source impedance
imbalance, operating gain, and board layout. The addition of
a small bypass capacitor of 5pF to 50pF directly between the
inputs of the IA will generally eliminate any positive feed-
back. CMR errors due to the input impedance mismatch will
also be reduced by the capacitor.
Another distinct advantage of the INA110 is the high fre-
quency CMR response. High frequency noise and sharp
common-mode transients will be rejected. To preserve AC
CMR, be sure to minimize stray capacitance on the input
lines. Matching the RCs in the two inputs will help to
maintain high AC CMR.
APPLICATIONS
In addition to general purpose uses, the INA110 is designed
to accurately handle two important and demanding applica-
tions: (1) inputs with high source impedances such as
capacitance/crystal/photodetector sensors and low-pass
filters and series-input protection devices, and (2) rapid-
scanning data acquisition systems requiring fast settling
time. Because the user has access to the output sense, current
sources can also be constructed using a minimum of external
components. Figures 6 through 19 show application circuits.
The INA110 is designed for fast settling with easy gain
selection. It has especially excellent settling in high gain. It
can also be used in fast-settling unity-gain applications. As
with all such amplifiers, the INA110 does exhibit significant
gain peaking when set to a gain of 1. It is, however,
unconditionally stable. The gain peaking can be cancelled
by band-limiting the negative input to 400kHz with a simple
external RC circuit for applications requiring flat response.
CMR is not affected by the addition of the 400kHz RC in a
gain of 1.
+15V
1
8
16
X200
10
6
9
VOUT
INA110
3
2
7
Transducer
–15V
FIGURE 6. Transformer-Coupled Amplifier.
+15V
1
8
INA110
7
+15V
16
10
6
VOUT
X200
9
1
∆
VIN
3
2
8
12
10
6
X100
1MΩ
9
VOUT
INA110
3
2
–15V
7
Thermocouple
Transducer or
Other Floating
Source
100Ω
–15V
OPA121
Divider minimizes degredation of CMR due to
distributed capacitance on the input lines.
FIGURE 7. Floating Source Instrumentation Amplifier.
FIGURE 8. Instrumentation Amplifier with Shield Driver.
INA110
10
SBOS147A
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TI [ TEXAS INSTRUMENTS ]
