7

®

INA157

APPLICATIONS INFORMATION

The INA157 is a difference amplifier suitable for a wide

range of general-purpose applications. Figure 1 shows the

basic G = 1/2 configuration. The input and feedback resis-

tors can be reversed to achieve G = 2, as shown in Figure 2.

For applications requiring G = 1, the INA154 is recom-

mended.

Decoupling capacitors are strongly recommended for appli-

cations with noisy or high impedance power supplies. The

capacitors should be placed close to the device pins as

shown in Figure 1.

As shown in Figure 1, the output is referred to the reference

terminal (pin 1). A voltage applied to this pin will be

summed with the output signal. The differential input signal

is connected to pins 2 and 3. The source impedances con-

nected to the inputs must be nearly equal to assure good

common-mode rejection. A 5

Ω mismatch in source imped-

ance will degrade the common-mode rejection of a typical

device to approximately 77dB (RTO). If the source has a

known impedance mismatch, an additional resistor in series

with the opposite input can be used to preserve good com-

mon-mode rejection.

V

3

5

6

3

1

Ref

INA157

V

2

R

3

12k

Ω

R

1

12k

Ω

R

2

6k

Ω

R

4

6k

Ω

R

L

V

2

–In

+In

1

µF

V–

4

1

µF

V+

7

FIGURE 1. G = 1/2 Differential Amplifier (basic power

supply and signal connections).

FIGURE 2. G = 2 Differential Amplifier.

V

3

5

6

3

V

O

INA157

V

Offset Adjustment

Range =

±1mV

G = 1/2

2

R

4

6k

Ω

V

2

20

Ω

250k

Ω

10

Ω

100k

Ω

+15V

–15V

1

R

3

12k

Ω

R

1

12k

Ω

R

2

6k

Ω

FIGURE 3. Offset Adjustment.

OPERATING VOLTAGE

The INA157 operates from

±4V to ±18V supplies with

excellent performance. Most behavior remains unchanged

throughout the full operating voltage range. Parameters

which vary significantly with operating voltage are shown in

the Typical Performance Curves.

INPUT VOLTAGE RANGE

The INA157 can accurately measure differential signals

that are above the positive or negative power supply rail. In

a gain of 1/2, the linear common-mode range extends from

3•(V+) – 7.5V to 3•(V–) +7.5V. See the Typical Perfor-

mance Curve, “Input Common-Mode Range vs Output

Voltage.”

OFFSET VOLTAGE TRIM

The INA157 is laser trimmed for low offset voltage and

drift. Most applications require no external offset adjust-

ment. Figure 3 shows an optional circuit for trimming the

output offset voltage. The output is referred to the output

reference terminal (pin 1), which is normally grounded. A

voltage applied to the Ref terminal will be summed with the

output signal. This can be used to null offset voltage as

shown in Figure 3. The source impedance of a signal

applied to the Ref terminal should be less than 10

Ω to

maintain good common-mode rejection.

V

3

2

6

1

INA157

V

5

R

4

6k

Ω

R

3

12k

Ω

R

2

6k

Ω

R

1

12k

Ω

V

2

–In

+In

3

Ref

R

L