Datasheet
OP297
Rev. G | Page 11 of 16
APPLICATION CIRCUITS
PRECISION ABSOLUTE VALUE AMPLIFIER
The circuit in Figure 31 is a precision absolute value amplifier
with an input impedance of 30 MΩ. The high gain and low
TCV
OS
of the OP297 ensure accurate operation with microvolt
input signals. In this circuit, the input always appears as a
common-mode signal to the op amps. The CMR of the OP297
exceeds 120 dB, yielding an error of less than 2 ppm.
+15V
–15V
5
6
7
1
3
4
–
+
1/2
OP297
–
+
1/2
OP297
2
8
R1
1kΩ
R3
1kΩ
D1
1N4148
D2
1N4148
R2
2kΩ
0V < V
OUT
< 10V
C1
30pF
C2
0.1µF
C3
0.1µF
V
IN
00300-031
Figure 31. Precision Absolute Value Amplifier
PRECISION CURRENT PUMP
Maximum output current of the precision current pump shown
in Figure 32 is ±10 mA. Voltage compliance is ±10 V with
±15 V supplies. Output impedance of the current transmitter
exceeds 3 M with linearity better than 16 bits. R1 through R4
should be matched resistors.
+15V
5
6
7
1
2
8
3
–15V
–
+
1/2
OP297
–
+
1/2
OP297
R1
10kΩ
R2
10kΩ
V
IN
R3
10kΩ
R4
10kΩ
R5
100kΩ
I
OUT
10mA MAX
I
OUT
= = = 10mA/V
V
IN
R5
V
IN
100Ω
00300-032
Figure 32. Precision Current Pump
PRECISION POSITIVE PEAK DETECTOR
In Figure 33, the C
H
must be of polystyrene, Teflon®, or
polyethylene to minimize dielectric absorption and leakage.
The droop rate is determined by the size of C
H
and the bias
current of the OP297.
2N930
+15V
1N4148
RESET
V
IN
5
6
7
1
3
–15V
–
+
1/2
OP297
–
+
1/2
OP297
2
1kΩ
1kΩ
1kΩ
1kΩ
C
H
0.1µF
0.1µF
V
OUT
00300-033
Figure 33. Precision Positive Peak Detector
SIMPLE BRIDGE CONDITIONING AMPLIFIER
Figure 34 shows a simple bridge conditioning amplifier using
the OP297. The transfer function is
R
R
RR
R
VV
F
REF
OUT
⎟
⎠
⎞
⎜
⎝
⎛
Δ+
Δ
=
The REF43 provides an accurate and stable reference voltage for
the bridge. To maintain the highest circuit accuracy, R
F
should
be 0.1% or better with a low temperature coefficient.
15
V
3
2
1
5
6
7
4
8
REF43
4
–
+
1/2
OP297
–
+
1/2
OP297
V
REF
R
F
R + ΔR
V
OUT
V
OUT
= V
REF
ΔR
R + ΔR
R
F
R
00300-034
Figure 34. Simple Bridge Condition Amplifier Using the OP297