OP113/OP213/OP413
REV. C –5–
2 mV trim range may be somewhat excessive. Reducing the
trimming potentiometer to a 2 kΩ value will give a more reason-
able range of ±400 µV.
16
2
13
6
711 12
4
14
15
9
1
3
AD588BD
8
10
3
2
8
1
R5
1kV
A2
2N2219A
+10.000V
+15V
–15V
10mF
1/2
OP213
+10.000V
6
5
4
7
1/2
OP213
A1
R3
17.2kV
0.1%
R4
500V
CMRR TRIM
10-TURN
T.C. LESS THAN 50ppm/8C
OUTPUT
0 10V
F.S.
–15V
350V
LOAD
CELL
100mV
F.S.
R1
17.2kV
0.1%
R2
301V
0.1%
Figure 1. Precision Load Cell Scale Amplifier
APPLICATION CIRCUITS
A High Precision Industrial Load-Cell Scale Amplifier
The OP113 family makes an excellent amplifier for conditioning
a load-cell bridge. Its low noise greatly improves the signal reso-
lution, allowing the load cell to operate with a smaller output
range, thus reducing its nonlinearity. Figure 1 shows one half of
the OP113 family used to generate a very stable 10.000 V bridge
excitation voltage while the second amplifier provides a differen-
tial gain. R4 should be trimmed for maximum common-mode
rejection.
A Low Voltage Single Supply, Strain-Gage Amplifier
The true zero swing capability of the OP113 family allows the
amplifier in Figure 2 to amplify the strain-gage bridge accurately
even with no signal input while being powered by a single +5
volt supply. A stable 4.000 V bridge voltage is made possible by
the rail-to-rail OP295 amplifier, whose output can swing to
within a millivolt of either rail. This high voltage swing greatly
increases the bridge output signal without a corresponding in-
crease in bridge input.
3
2
8
1
2N2222A
2.500V
1/2
OP295
4
2
4
6
IN
OUT
GND
REF43
R8
12.0kV
R7
20.0kV
4.000V
350V
35mV
F.S.
+5V
1/2
OP213
1
3
2
8
6
5
4
7
R4
100kV
R3
20kV
R6
27.4V
R5
2.10kV
R2
20kV
R1
100kV
1/2
OP295
R
G
= 2,127.4V
+5V
OUTPUT
0V 3.5V
Figure 2. Single Supply Strain-Gage Amplifier
APPLICATIONS
The OP113, OP213 and OP413 form a new family of high
performance amplifiers that feature precision performance in
standard dual supply configurations and, more importantly,
maintain precision performance when a single power supply is
used. In addition to accurate dc specifications, it is the lowest
noise single supply amplifier available with only 4.7 nV/
√
Hz
typical noise density.
Single supply applications have special requirements due to the
generally reduced dynamic range of the output signal. Single
supply applications are often operated at voltages of +5 volts or
+12 volts, compared to dual supply applications with supplies of
±12 volts or ±15 volts. This results in reduced output swings.
Where a dual supply application may often have 20 volts of
signal output swing, single supply applications are limited to, at
most, the supply range and, more commonly, several volts be-
low the supply. In order to attain the greatest swing the single
supply output stage must swing closer to the supply rails than in
dual supply applications.
The OP113 family has a new patented output stage that allows
the output to swing closer to ground, or the negative supply,
than previous bipolar output stages. Previous op amps had
outputs that could swing to within about ten millivolts of the
negative supply in single supply applications. However, the
OP113 family combines both a bipolar and a CMOS device in
the output stage, enabling it to swing to within a few hundred
microvolts of ground.
When operating with reduced supply voltages, the input range is
also reduced. This reduction in signal range results in reduced
signal-to-noise ratio, for any given amplifier. There are only two
ways to improve this: increase the signal range or reduce the
noise. The OP113 family addresses both of these parameters.
Input signal range is from the negative supply to within one
volt of the positive supply over the full supply range. Com-
petitive parts have input ranges that are a half a volt to five
volts less than this. Noise has also been optimized in the OP113
family. At 4.7 nV/√
Hz, it is less than one fourth that of competi-
tive devices.
Phase Reversal
The OP113 family is protected against phase reversal as long as
both of the inputs are within the supply ranges. However, if there
is a possibility of either input going below the negative supply
(or ground in the single supply case), the inputs should be pro-
tected with a series resistor to limit input current to 2 mA.
OP113 Offset Adjust
The OP113 has the facility for external offset adjustment, using
the industry standard arrangement. Pins 1 and 5 are used in
conjunction with a potentiometer of 10 kΩ total resistance,
connected with the wiper to V– (or ground in single supply
applications). The total adjustment range is about ±2 mV using
this configuration.
Adjusting the offset to zero has minimal effect on offset
drift (assuming the potentiometer has a tempco of less than
1000 ppm/°C). Adjustment away from zero, however, (like all
bipolar amplifiers) will result in a TCV
OS
of approximately
3.3 µV/°C for every millivolt of induced offset.
It is therefore not generally recommended that this trim be used
to compensate for system errors originating outside of the
OP113. The initial offset of the OP113 is low enough that
external trimming is almost never required but, if necessary, the
