OP497
OPEN-LOOP GAIN LINEARITY
PRECISION CURRENT PUMP
The OP497 has both an extremely high gain of 2000 V/mv mini-
mum and constant gain linearity. This enhances the precision of
the OP497 and provides for very high accuracy in high closed-loop
gain applications. Figure 5 illustrates the typical open-loop gain
linearity of the OP 497 over the military temperature range.
DIFFERENTIAL INPUT VOLTAGE – 10µV/ DIV
Maximum output current of the precision current pump shown
in Figure 7 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
10k
R
L
= 10k
V
S
= 15V
V
CM
= 0V
T
A
= +125 C
–
VIN
+
R1
10k
R2
10k
2
1/4
3
OP497
1
+15V
8
R5
10k
I
OUT
10mA
T
A
= +25C
R4
10k
V
V
I
OUT
=
IN
=
IN
= 10mA/ V
R5 100
5
6
7
1/4
OP497
4
T
A
= –55 C
–15V
Figure 7. Precision Current Pump
PRECISION POSITIVE PEAK DETECTOR
–15
–10
–5
0
5
10
15
OUTPUT VOLTAGE – Volts
Figure 5. Open-Loop Linearity of the OP497
APPLICATIONS
Precision Absolute Value Amplifier
In Figure 8, the CH must be of polystyrene, Teflon*, or polyeth-
ylene to minimize dielectric absorption and leakage. The droop
rate is determined by the size of CH and the bias current of the
OP497.
1k
+15V
0.1 F
6
2N930
1k
C
H
1k
5
1/4
8
The circuit of Figure 6 is a precision absolute value amplifier
with an input impedance of 30 MΩ. The high gain and low
TCV
OS
of the OP497 ensure accurate operation with microvolt
input signals. In this circuit, the input always appears as a com-
mon-mode signal to the op amps. The CMR of the OP497
exceeds 120 dB, yielding an error of less than 2 ppm.
+15V
1N4148
2
1/4
V
IN
1k
3
1
OP497
OP497
4
7
V
OUT
0.1 F
–15V
RESET
R1
1k
C1
30pF
D1
1N4148
R3
1k
C2
0.1 F
Figure 8. Precision Positive Peak Detector
SIMPLE BRIDGE CONDITIONING AMPLIFIER
6
1/4
2
3
8
1/4
1
D2
1N4148
R2
2k
OP497
C3
4 0.1 F
5
OP497
7
0V < V
OUT
< 10V
Figure 9 shows a simple bridge conditioning amplifier using
the OP497. The transfer function is:
V
IN
∆
R
R
F
V
OUT
=
V
REF
R
+ ∆
R
R
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.
–15V
Figure 6. Precision Absolute Value Amplifier
*Teflon
is a registered trademark of the Dupont Company.
–8–
REV. D
AD [ ANALOG DEVICES ]
