®

INA111

10

FIGURE 7. Bridge Transducer Amplifier.

mismatched values, causes a high frequency common-mode

signal to be converted to a differential signal. This degrades

common-mode rejection. The differential input capacitor,

C3, reduces the bandwidth and mitigates the effects of

mismatch in C1 and C2. Make C3 much larger than C1 and

C2. If properly matched, C1 and C2 also improve CMR.

OUTPUT VOLTAGE SENSE

(SOL-16 Package Only)

The surface-mount version of the INA111 has a separate

output sense feedback connection (pin 12). Pin 12 must be

connected, usually to the output terminal, pin 11, for proper

operation. (This connection is made internally on the DIP

version of the INA111.)

The output feedback connection can be used to sense the

output voltage directly at the load for best accuracy. Figure 8

shows how to drive a load through series interconnection

resistance. Remotely located feedback paths may cause

instability. This can be generally be eliminated with a high

frequency feedback path through C1.

FIGURE 6. Input Low-Pass Filter.

FIGURE 8. Remote Load and Ground Sensing.

INA111

R

G

100

Ω

V

O

+10V

Bridge

G = 500

Ref

INA111

V

O

V

IN

–

V

IN

+

R

1

R

2

C

3

C

1

C

2

R

1 = R2

C

1 = C2

C

3 ≈ 10C1

Ref

INA111

R

G

V

IN

–

V

IN

+

Load

Equal resistance here preserves

good common-mode rejection.

C

1

1000pF

Feedback

Ref

Surface-mount package

version only.

FIGURE 9. High-Pass Input Filter.

INA111

C

1

C

2

R

1

R

2

V

O

2

πR

1C1

1

f

c =

NOTE: To preserve good low frequency CMR,

make R

1 = R2 and C1 = C2.

R

G

Ref

f

−3dB =

1

4

π R

1

C

3 +

C

1

2









FIGURE 10. Galvanically Isolated Instrumentation

Amplifier.

INA111

ISO122

±6V to ±18V

Isolated Power

±15V

Ref

V

IN

–

V

IN

+

V

O

Isolated

Common

V+

V–