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InGaAs Biased Detector Chapter 5: Common Operating Circuits
Page 10 15830-D02
One can also use a photodetector with an amplifier for the purpose of achieving
high gain. The user can choose whether to operate in Photovoltaic of
Photoconductive modes. There are a few benefits of choosing this active circuit:

Photovoltaic Mode: We maintain the circuit at zero volts across the
photodiode, holding point A at the same potential as point B by the
operational amplifier. This eliminates the possibility of dark current.

Photoconductive mode: We reverse bias the photodiode; it improves the
bandwidth while lowering the junction capacitance. The gain of the
detector is dependent on the feedback element (R
F
). The bandwidth of
the detector can be calculated using the following:
3
4
,
Where GBP is the amplifier product gain-bandwidth and C
D
is the sum
of the junction capacitance, amplifier capacitance, and feedback
capacitance.