changed, pins 2 and 5 must also be interchanged to maintain
proper ratio matching.
APPLICATIONS INFORMATION
The INA133 and INA2133 are high-speed difference ampli-
fiers suitable for a wide range of general purpose applica-
tions. Figure 1 shows the basic connections required for
operation of the INA133. Decoupling capacitors are strongly
recommended in applications 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-circuited.
OPERATING VOLTAGE
The INA133 and INA2133 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.
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 80dB (a 10Ω mismatch degrades CMR to
74dB). 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.
INPUT VOLTAGE
The INA133 and INA2133 can accurately measure differen-
tial signals that are above and below the supply rails. Linear
common-mode range extends from 2 • (V+)–3V to 2 • (V–)
+3V (nearly twice the supplies). See the typical performance
curve, “Input Common-Mode Voltage vs Output Voltage.”
OFFSET VOLTAGE TRIM
The INA133’s internal resistors are accurately ratio trimmed
to match. That is, R1 is trimmed to match R2 and R3 is
trimmed to match R4. However, the absolute values may not
be equal (R1 + R2 may be slightly different than R3 + R4).
Thus, large series resistors on the input (greater than 250Ω),
even if well matched, will degrade common-mode rejection.
The INA133 and INA2133 are laser trimmed for low offset
voltage and drift. Most applications require no external offset
adjustment. Figure 2 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 2. The source impedance of a signal applied
to the Ref terminal should be less than 10Ω to maintain good
common-mode rejection.
Circuit board layout constraints might suggest possible varia-
tions in connections of the internal resistors. For instance, it
appears that pins 1 and 3 could be interchanged. However,
because of the ratio trimming technique used (see paragraph
above) CMRR will be degraded. If pins 1 and 3 are inter-
INA133
R1
R2
V–
V+
2
5
6
V2
1µF
1µF
4
7
VO
INA133
R1
R2
25kΩ
25kΩ
10
R3
Ω
–In
V2
2
5
6
3
V3
R4
+15V
V
OUT = V3 – V2
Gain Error = ±0.01%
CMR = 90dB
Nonlinearity = ±0.0001%
1
R3
25kΩ
R4
25kΩ
V
O = V3 – V2
150k
Ω
Offset Adjustment
Range = ±1mV
+In
V3
100k
Ω
1
3
10
Ω
–15V
FIGURE 1. Precision Difference Amplifier (Basic Power
Supply and Signal Connections).
FIGURE 2. Offset Adjustment.
®
9
INA133, INA2133
BB [ BURR-BROWN CORPORATION ]
