Datasheet
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 5Ω 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
O
= 1/2 (V
3
–
V
2
)
2
R
3
12kΩ
R
1
12kΩ
R
2
6kΩ
R
4
6kΩ
R
L
V
2
–In
+In
1µF
V–
4
1µF
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
O
= 1/2 (V
3
–
V
2
)
Offset Adjustment
Range = ±1mV
G = 1/2
2
R
4
6kΩ
V
2
20Ω
250kΩ
10Ω
100kΩ
+15V
–15V
1
R
3
12kΩ
R
1
12kΩ
R
2
6kΩ
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 10Ω to
maintain good common-mode rejection.
V
3
2
6
1
INA157
V
O
= 2 (V
3
–
V
2
)
5
R
4
6kΩ
R
3
12kΩ
R
2
6kΩ
R
1
12kΩ
V
2
–In
+In
3
Ref
R
L