Extended InGaAs Biased Detector
Chapter 5: Common Operating Circuits
Page 10
TTN134037-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: The circuit is held at zero volts across the
photodiode, since point A is held at the same potential as point B by the
operational amplifier. This eliminates the possibility of dark current.
Photoconductive mode: The photodiode is reversed biased, thus
improving 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 gain bandwidth product and C
D
is the sum of
the junction capacitance, amplifier capacitance, and feedback
capacitance.
