B

¨ )$9

2

LE D

Driver

LE D

Photo-

Diode

+

±

R

F

-V

BIAS

C

D

C

F

OP Ax863

To

ADC

V

OUT

V

S+

V

S-

I

D

Time (150 ns/div)

-2

0

-1.5

0.1

-1

0.2

-0.5

0.3

0

0.4

0.5

0.5

1

0.6

1.5

0.7

2

0.8

2.5

0.9

3

1

3.5

1.1

4

1.2

D805

OPAx863 O/P

S/H Voltage

% Error

14

OPA2863

SBOS982A – JUNE 2020 – REVISED JUNE 2020

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Product Folder Links: OPA2863

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Copyright © 2020, Texas Instruments Incorporated

Figure 11. 0.1% Settling Performance

9.3 Transimpedance Amplifier

The high GBWP and small input capacitance of the OPAx863 devices make them an ideal wideband

transimpedance amplifier for high-frequency, mid to high transimpedance gain applications.

Figure 12. Wideband, High-Sensitivity, Transimpedance Amplifier

9.3.1 Design Requirements

Table 2 lists the design requirements for a high-bandwidth, high-gain transimpedance amplifier circuit.

Table 2. Design Requirements

PARAMETER

DESIGN REQUIREMENT

Target bandwidth

> 2.5 MHz

Transimpedance gain

100 kΩ

Photodiode capacitance

10 pF

9.3.2 Detailed Design Procedure

Figure 12 shows how the OPAx863 devices can be used as a transimpedance amplifier (TIA) for converting a

photodiode current into an output voltage. The factors which determine the minimum required gain-bandwidth

product (GBW) of the amplifier are the transimpedance gain, small-signal bandwidth and the photodiode

capacitance. Increase in the values of any of these three parameters requires higher GBW. Large-area

photodiodes with higher sensitivity have a relatively larger photodiode capacitance, sometimes up to 100 pF,

which impacts the small-signal bandwidth, which is given below.