OP497GSZ Datasheet, PDF (12/16 Pages) Analog Devices – Precision Picoampere Input Current Quad Operational Amplifier

OP497
APPLICATIONS CIRCUIT
PRECISION ABSOLUTE VALUE AMPLIFIER
The circuit in Figure 36 is a precision absolute value amplifier
with an input impedance of 30 MΩ. The high gain and low
TCVOS of the OP497 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 OP497 exceeds
120 dB, yielding an error of less than 2 ppm.
+15V
C2
0.1µF
R1
R3
1kΩ
1kΩ
C1
30pF
2
8
1/4
1
OP497
V_IN ³
C3
4 _0.1µF
D1
1N4148
D2
1N4148
6
1/4
7
OP497
5
0V < V_OUT < 10V
R2
2kΩ
–15V
Figure 36. Precision Absolute Value Amplifier
PRECISION CURRENT PUMP
Maximum output current of the precision current pump shown
in Figure 37 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.
R1
10kΩ
–
V_IN
R2
10kΩ
+
R3
10kΩ
2
1/4
OP497
3
R5
1
10kΩ
+15V
I_OUT
±10mA
R4
10kΩ
I_OUT
=
V_IN
R5
= ^VIN
100Ω
=
10mA/V
8
5
7
1/4
OP497
6
4
–15V
Figure 37. Precision Current Pump
PRECISION POSITIVE PEAK DETECTOR
In Figure 38, 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 OP497.
2
1/4
1
V_IN ^{1kΩ 3 OP497}
1kΩ
1N4148
+15V
0.1µF
2N930
C_H ⁺
6
8
1/4
7
1kΩ ₅ ^OP497
4 _0.1µF
V_OUT
1kΩ
RESET
–15V
Figure 38. Precision Positive Peak Detector
SIMPLE BRIDGE CONDITIONING AMPLIFIER
Figure 39 shows a simple bridge conditioning amplifier using
the OP497. 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.
+5V
2
REF43 ^{6 2.5V VREF}
R
R
4
R
R + ΔR
R_F
2
1/4
1
OP497
3
V_OUT
+5V
6
8
1/4
7
5 ^OP497
4
( ) ^VOUT ^{= V}REF
ΔR
R + ΔR
R_F
R
–5V
Figure 39. Simple Bridge Conditioning Amplifier Using the OP497
Rev. E | Page 12 of 16