APPLICATIONS INFORMATION
The INA137 and INA2137 are differential line receivers
suitable for a wide range of audio and general-purpose
applications. Figure 1 shows the basic G = 1/2 (–6dB)
differential receiver configuration. The input and feedback
resistors can be reversed to achieve G = 2 (+6dB), as shown
in Figure 2. For applications requiring G = 1 (0dB), the
INA134 and INA2134 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 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 common-
mode rejection.
The INA137 and INA2137 have excellent distortion charac-
teristics. THD+Noise is below 0.001% throughout the audio
frequency range. Up to approximately 10kHz distortion is
below the measurement limit of commonly used test equip-
ment. Furthermore, distortion remains relatively flat over its
wide output voltage swing range (approximately 1.7V from
either supply).
OFFSET VOLTAGE TRIM
The INA137 and INA2137 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.
INA137
–In
V
2
R
2
5
6kΩ
12kΩ
6
R
1
2
V–
1µF
4
INA137
–In
V
2
R
1
2
12kΩ
6kΩ
R
2
V+
1µF
7
+In
V
3
R
4
1
6kΩ
12kΩ
R
3
V
O
= 2 (V
3
– V
2
)
3
5
FIGURE 2. G = 2 Differential Receiver.
6
V
O
= 1/2 (V
3
– V
2
)
G = 1/2
R
1
12kΩ
INA137
R
2
6kΩ
+In
V
3
R
3
3
12kΩ
R
4
1
6kΩ
V
2
2
5
6
FIGURE 1. G = 1/2 Differential Receiver (Basic Power
Supply and Signal Connections).
20Ω
V
3
3
V
O
R
3
12kΩ
AUDIO PERFORMANCE
The INA137 and INA2137 were designed for enhanced ac
performance. Very low distortion, low noise, and wide band-
width provide superior performance in high quality audio
applications. Laser-trimmed matched resistors provide opti-
mum common-mode rejection (typically 90dB), especially
when compared to circuits implemented with an op amp
and discrete precision resistors. In addition, high slew rate
(14V/µs) and fast settling time (3µs to 0.01%) ensure excel-
lent dynamic performance.
®
R
4
6kΩ
+15V
V
O
= 1/2 (V
3
– V
2
)
Offset Adjustment
Range = ±1mV
1
250kΩ
100kΩ
10Ω
–15V
FIGURE 3. Offset Adjustment.
INA137, INA2137
8
BURR-BROWN [ BURR-BROWN CORPORATION ]
