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

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

–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 < VOUT < 10V

C1

30pF

C2

0.1µF

C3

0.1µF

VIN

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. 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

VIN

R3

10kΩ

R4

10kΩ

R5

100kΩ

IOUT

10mA MAX

IOUT =

=

= 10mA/V

VIN

R5

VIN

100Ω

Figure 32. Precision Current Pump

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.

2N930

+15V

1N4148

RESET

VIN

5

6

7

1

3

–15V

–

+

1/2

OP297

–

+

1/2

OP297

2

1kΩ

1kΩ

1kΩ

1kΩ

CH

0.1µF

0.1µF

VOUT

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

R

R

R

V

V

F

REF

OUT

⎟

⎠

⎞

⎜

⎝

⎛

Δ

+

Δ

=

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

3

2

1

5

6

7

4

8

REF43

4

–

+

1/2

OP297

–

+

1/2

OP297

VREF

RF

R + ΔR

VOUT

VOUT = VREF

ΔR

R + ΔR

RF

R

Figure 34. Simple Bridge Condition Amplifier Using the OP297