Datasheet

9
®
INA143, INA2143
APPLICATIONS INFORMATION
The INA143 and INA2143 are high-speed difference ampli-
fiers suitable for a wide range of general-purpose applica-
tions. Figure 1 shows the basic G = 10 configuration. The
input and feedback resistors can be reversed to achieve
G = 0.1, as shown in Figure 2. For applications requiring
G = 1, the INA133 and INA2133 are recommended.
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. All circuitry is completely independent
in the dual version assuring lowest crosstalk and normal
behavior when one amplifier is overdriven or short-cir-
cuited.
As shown in Figure 1, the differential input signal is con-
nected to pins 2 and 3. The source impedances connected to
the inputs must be nearly equal to assure good common-
mode rejection. A 5Ω mismatch in source impedance will
degrade the common-mode rejection of a typical device to
approximately 86dB (RTI). If the source has a known
impedance mismatch, an additional resistor in series with
the opposite input can be used to preserve good common-
mode rejection.
The INA143’s internal resistors are accurately ratio trimmed
to match. That is, R
1
/R
2
and R
3
/R
4
are trimmed to equal 0.1.
However, the absolute values may not be equal (R
1
+ R
2
may
be slightly different than R
3
+ R
4
). Thus, large series resistors
on the input (greater than 100Ω), even if well matched, will
degrade common-mode rejection.
V
3
5
6
1
3
INA143
V
O
= 10 (V
3
– V
2
)
2
R
3
10kΩ
R
4
100kΩ
R
1
10kΩ
R
2
100kΩ
V
2
–In
+In
1µF
V–
4
1µF
V+
7
FIGURE 1. G = 10 Basic Power Supply and Signal Connections.
OPERATING VOLTAGE
The INA143 and INA2143 operate from single (+4.5V to
+36V) or dual (±2.25V to ±18V) supplies with excellent
performance. Specifications are production tested with ±5V
and ±15V supplies. Most behavior remains unchanged
throughout the full operating voltage range. Parameters which
vary significantly with operating voltage are shown in the
Typical Performance Curves.
OFFSET VOLTAGE TRIM
The INA143 and INA2143 are laser trimmed for low offset
voltage and drift. Most applications require no external offset
adjustment. 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
3
1
INA143
V
O
= 0.1 (V
3
– V
2
)
5
R
4
100kΩ
R
3
10kΩ
R
2
100kΩ
R
1
10kΩ
V
2
–In
+In
FIGURE 2. G = 0.1 Difference Amplifier.
FIGURE 3. Offset Adjustment.
V
3
5
6
3
V
O
INA143
V
O
= 10 (V
3
– V
2
)
Offset Adjustment
Range = ±3mV
Compensates
for impedance at
pin 1—see text.
G = 10
2
R
4
100kΩ
V
2
10Ω
499kΩ
100Ω
100kΩ
+15V
–15V
1
R
3
10kΩ
R
1
10kΩ
R
2
100kΩ