REV. A

ADG781/ADG782/ADG783

–6–

FREQUENCY – Hz

–30

–40

–110

–120

–130

10k

100k

1M

10M

100M

–100

–90

–80

–70

–60

–50

TPC 5. Off Isolation vs. Frequency

FREQUENCY – Hz

–30

–40

–110

–120

–130

10k

100k

1M

10M

100M

–100

–90

–80

–70

–60

–50

TPC 6. Crosstalk vs. Frequency

FREQUENCY – Hz

0

–6

10k

100k

1M

10M

100M

–4

–2

TPC 7. On Response vs. Frequency

SOURCE VOLTAGE – V

25

–10

0

0.5

–5

0

20

15

10

5

1

1.5

2

2.5

3

3.5

4

4.5

5

TPC 8. Charge Injection vs. Source Voltage

APPLICATIONS

Figure 1 illustrates a photodetector circuit with programmable

gain. An AD820 is used as the output operational amplifier.

With the resistor values shown in the circuit, and using different

combinations of the switches, gain in the range of 2 to 16 can

be achieved.

5V

2.5V

R3

510k

C1

GND

D1

S1

D1

GAIN RANGE 2 TO 16

5V

AD820

S2

D2

S3

D3

S4

D4

(LSB) IN1

IN2

IN3

(MSB) IN4

R4

240k

R5

240k

R6

120k

R7

120k

R8

120k

R9

120k

R10

120k

R1

33k

R2

510k

2.5V

Figure 1. Photodetector Circuit with Programmable Gain