9.1.2 Wideband, Transimpedance Design Using OPA817

The OPA817 design is optimized for wideband, low-noise transimpedance applications with high GBWP, low-

input voltage, current noise, and low input capacitance. The high voltage capability allows greater flexibility

of supply voltages along with wider output voltage swings. Figure 9-3 shows an example circuit of a typical

photodiode amplifier circuit. As Figure 9-3 shows, the photodiode is generally reverse biased in a TIA application

so that the photodiode current in the circuit of flows into the op amp feedback path. This results in an output

valid range of the OPA817.

1. The op amp GBWP.

(common-mode and differential capacitance), and PCB parasitic capacitance.

V

O

+5 V

–5 V

+

–

R

F

C

F

V

BIAS

OPA817

V

REF

C

TOT

Figure 9-3. Wideband, Low-Noise, Transimpedance Amplifier

Equation 1 shows the relationship between the above mentioned three elements for a Butterworth response.

3dB

F

TOT

GBWP

f

2 R C

S

(1)

in instability if left uncompensated. To counteract the effect of the zero, a pole is inserted in the noise gain by

report discusses theories and equations that show how to compensate a transimpedance amplifier for a

particular gain and input capacitance. The bandwidth and compensation equations from the application report

1 provides a link to the calculator. As shown in Figure 9-3, the details of maximizing the dynamic range of TIA

front-ends are provided in the Maximizing the Dynamic Range of Analog TIA Front-End application note.

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OPA817

SBOS847 – JULY 2022

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