Page 72 - Photodetection and Measurement - Maximizing Performance in Optical Systems
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Fundamental Noise Basics and Calculations
Fundamental Noise Basics and Calculations 65
-45
-50
330pF
-55
Voltage (dBm) -60 100pF
-65
-70
-75
-80
16pF
-85
0 5,000 10,000 15,000 20,000
Frequency (Hz)
Figure 3.12 Measured noise peaking for three values of photodiode capacitance.
-40
TL071
-50
Voltage (dBm) -60 LMC7101
-70
-80
OPA121
-90
0 5,000 10,000 15,000 20,000
Frequency (Hz)
Figure 3.13 Measured noise spectra of 100MW transimpedance amp with three
opamp types.
3.11.5 Discrete front ends
When we need to use a physically large and therefore high-capacitance photo-
detector, this is one situation where a discrete transistor front end can be
very useful. Here the dominant noise source at anything above a few hertz is
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