OP297_06 Datasheet, PDF (11/16 Pages) Analog Devices – Dual Low Bias Current Precision Operational Amplifier

APPLICATIONS
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
TCVOS 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
C2
0.1µF
R1
R3
1kΩ
1kΩ
C1
30pF
2_– ⁸
1/2 1
OP297
V_IN
3₊
C3
0.1µF
4
D1
1N4148
D2
1N4148
5_–
1/2
OP297
6₊
7
0V < V_OUT < 10V
R2
2kΩ
–15V
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 MΩ with linearity better than 16 bits.
R3
10kΩ
R1
10kΩ
2_–
R6
V_IN
R2
10kΩ
1/2 1
OP297
3₊
+15V
10kΩ
R4
85
10kΩ _{7 1/2}
OP297
6
I_OUT
10mA
I_OUT
=
V_IN
R5
= ^VIN
100Ω
= 10mA/V
–15V
Figure 32. Precision Current Pump
OP297
PRECISION POSITIVE PEAK DETECTOR
In Figure 33, the CH must be of polystyrene, Teflon®, or
polyethylene to minimize dielectric absorption and leakage.
The droop rate is determined by the size of CH and the bias
current of the OP297.
1kΩ
+15V
1N4148
0.1µF
2_–
1/2 1
V_IN
1kΩ ₃ ^OP297
+
RESET
1kΩ
6_–
1/2 7
1kΩ
OP297
5₊
C_H
0.1µF
2N930
–15V
V_OUT
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
V_OUT
= V_{REF ⎜⎝⎛}
R
ΔR
+ ΔR
⎟⎠⎞
R_F
R
The REF43 provides an accurate and stable reference voltage for
the bridge. To maintain the highest circuit accuracy, RF should
be 0.1% or better with a low temperature coefficient.
15V
REF43
4
V_REF
R + ΔR
R_F
2_–
1/2 1
OP297
3₊
V_OUT
6_– ⁸
1/2 7
OP297
5₊
4
V_OUT = V_REF
ΔR
R + ΔR
R_F
R
Figure 34. A Simple Bridge Condition Amplifier Using the OP297
Rev. F | Page 11 of 16