6

11

®

OPT301

A

1

V

O

C

1

0.1

µF

R

2

1M

Ω

R

1

1M

Ω

C

2

0.1

µF

R

3

100k

Ω

1M

Ω

R

f

20dB/decade

1M

Ω

OPT301

40pF

75

Ω

2

8

5

4

λ

FIGURE 12. DC Restoration Rejects Unwanted Steady-State Background Light.

FIGURE 13. 4-20mA Current-Loop Transmitter.

1M

Ω

OPT301

40pF

75

Ω

2

83

5

4

λ

1

4-20mA

(4mA Dark)

10V to 36V

100µA

1/2

REF200

100µA

1/2

REF200

20k

Ω

R

2

65

Ω

IN4148

2N2222

R

1

22.5k

Ω

Calculations shown provide a dark output of 4mA.

Output is 20mA at a photodiode current of

I

R

– 994,000

Ω

(1 – 2500 I

R

– 26,000

Ω

26,000

(1 – 2500 I