OP4177AR-REEL7 데이터 시트보기 (PDF) - Analog Devices

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OP4177AR-REEL7

Precision Low Noise, Low Input Bias Current Operational Amplifiers

Analog Devices 

OP1177/OP2177/OP4177

+15V

0.1µF

ADR421

4.12kΩ

4.37kΩ

500Ω

200Ω

4.12kΩ

100Ω

100Ω

20Ω

6

1/2

7

OP2177

5

VOUT

100Ω

V+

RTD

5kΩ

49.9kΩ

2

8

1/2 1

OP2177

3

4

VOUT

V–

Figure 65. Low Power Linearized RTD Circuit

SINGLE OPERATIONAL AMPLIFIER BRIDGE

The low input offset voltage drift of the OP1177 makes it very

effective for bridge amplifier circuits used in RTD signal condi-

tioning. It is often more economical to use a single bridge

operational amplifier as opposed to an instrumentation amplifier.

In the circuit shown in Figure 66, the output voltage at the

operational amplifier is

VO

=

R2

R

⎡

⎢

⎢⎢VREF

⎢⎣

⎜⎛

⎜

⎜

⎜⎝

δ

⎟⎞⎥⎤

⎟⎥

R1

R

+

⎜⎝⎛1 +

R1

R2

⎟⎠⎞

(1 +

δ)

⎟⎥

⎟⎠⎥⎦

where δ = ΔR/R is the fractional deviation of the RTD resistance

with respect to the bridge resistance due to the change in temper-

ature at the RTD.

For δ << 1, the preceding expression becomes

VO

≅

⎜⎝⎛

R2

R

⎟⎠⎞

VREF

⎜⎛

⎜

⎜⎜⎝ 1+

δ

R1 +

R

R1

R2

⎟⎞

⎟

⎟⎟⎠

=

⎢⎣⎡⎜⎝⎛

R2

R

⎟⎠⎞

⎜⎝⎛1

+

R1

R2

⎟⎠⎞

+

⎜⎝⎛

R1

R2

⎟⎠⎞⎥⎦⎤

VREF

δ

With VREF constant, the output voltage is linearly proportional

to δ with a gain factor of

VREF

⎜⎝⎛

R2

R

⎟⎠⎞

⎢⎣⎡⎜⎝⎛1 +

R1

R2

⎟⎠⎞ + ⎜⎝⎛

R1

R2

⎟⎠⎞⎥⎦⎤

15V

RF

0.1µF

ADR421

R

R

R(1+δ)

R

V+

2

7

6

OP1177

3

4

V–

VOUT

RF

Figure 66. Single Bridge Amplifier

Rev. E | Page 20 of 24

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