OPT101

9

SBBS002A

www.ti.com

This capacitor eliminates gain peaking and prevents

can be interpolated.

(b)-External Feedback

DC Gain

Bandwidth

(M

Ω)

(pF)

(kHz)

150

2

8

225

3

6

5

10

6

2.5

10

5

11

1.3

50

—

51

0.33

DC Gain

Bandwidth

(M

Ω)

(pF)

(kHz)

56

0.05

58

33

0.1

44

1

—

123

2

—

2

9.4

5

—

5

3.6

10

—

10

1.8

50

—

50

0.34

Note: (1) May require 1k

Ω in series with pin 5 when driving

large capacitances.

FIGURE 4. Changing Responsivity with External Resistor.

FIGURE 3. Dark Error (Offset) Adjustment Circuit.

CHANGING RESPONSIVITY

voltage responsivity. To increase the responsivity, this resistor

can be placed in series with the internal 1M

Ω (Figure 4a), or

the external resistor can replace the internal resistor by not

connecting pin 4 (Figure 4b). The second configuration also

external resistors of less than 1M

Ω.

Figure 4 includes tables showing the responsivity and

DARK ERRORS

The dark errors in the specification table include all sources.

The dominant source of dark output voltage is the “pedestal”

voltage applied to the non-inverting input of the op amp.

This voltage is introduced to provide linear operation in the

absence of light falling on the photodiode. Photodiode dark

current is approximately 2.5pA and contributes virtually no

offset error at room temperature. The bias current of the op

amp's summing junction (– input) is approximately 165pA.

The dark current will be subtracted from the amplifier's bias

current, and this residual current will flow through the

feedback resistor creating an offset. The effects of temperature

on this difference current can be seen in the typical

dark output voltage can be trimmed to zero with the optional

circuit shown in Figure 3. A low impedance offset driver (op

amp) should be used to drive pin 8 because this node has

signal-dependent currents.

+15V

–15V

–15V

OPA177

1M

Ω

OPT101

3pF

2

5

4

V

S

λ

3

8

V

B

8pF

1

Common

–V

R

1

500k

Ω

1/2 REF200

100

µA

V

O

Adjust R

1

for V

with no light.

1M

Ω

OPT101

3pF

2

5

4

V

S

λ

3

8

V

B

8pF

1

R

EXT

C

EXT

1M

Ω

OPT101

3pF

2

5

4

V

S

λ

3

8

V

B

8pF

1

R

EXT

C

EXT