THORLABS PDA36A2, Руководство пользователя

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Si Switchable Gain Detector Chapter 4: Operation
Rev A, December 27, 2017 Page 5
Material
Dark
Current
Speed
Sensitivity 1
(nm)
Cost
Silicon (Si) Low High 400 – 1000 Low
Germanium (Ge) High Low 900 – 1600 Low
Gallium Phosphide (GaP) Low High 150 – 550 Med
Indium Gallium Arsenide
(InGaAs)
Low High 800 – 1800 Med
Extended Range: Indium
Gallium Arsenide (InGaAs)
High High 1200 – 2600 High
4.4. Bandwidth and Response
For the PDA detectors, 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
photodiode junction capacitance and the amplifier capacitance.
4.5. Terminating Resistance
The maximum output of the PDA36A2 is 10 V for high impedance loads (i.e.
RLoad > 5 k
Ω ) and 5 V for 50 Ω loads. Adjust the gain so that the measured
signal level out of the PDA36A2 is below 10 V (5 V with a 50 Ω load) to avoid
saturation.
For low terminating resistors, <5 k Ω or 1% error, an additional factor needs to be
considered. The output of the PDA includes a 50 Ω series resistor (R
s
). The
output load creates a voltage divider with the 50 Ω series resistor as follows:

∗ ∗ ∗
4.6. Gain Adjustment
The PDA36A2 includes a low noise, low offset, high gain transimpedance
amplifier that allows gain adjustment over a 70 dB range. The gain is adjusted by
rotating the gain control knob, located on the top side of the unit. There are 8
gain positions incremented in 10 dB steps. It is important to note that the
bandwidth will decrease as the gain increases. See the specifications table on
page 7 to choose the best gain verse bandwidth for a given input signal.
1 Approximate values; actual wavelength values will vary.