Bandwidth And Response; Terminating Resistance; Gain Adjustment - THORLABS PDA36A2 User Manual

Si Switchable Gain Detector
Material
Silicon (Si)
Germanium (Ge)
Gallium Phosphide (GaP)
Indium Gallium Arsenide
(InGaAs)
Extended Range: Indium
Gallium Arsenide (InGaAs)

4.4. Bandwidth and Response

For the PDA detectors, the gain of the detector is dependent on the feedback
element (R ). The bandwidth of the detector can be calculated using the
f
following:
Where GBP is the amplifier gain bandwidth product and C
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 kΩ) 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 kΩ or 1% error, an additional factor needs to be
considered. The output of the PDA includes a 50 Ω series resistor (R
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.
Rev A, December 27, 2017
Dark
Current
3
∗
Speed
Low High
High Low
Low High
Low High
High High
4
∗
Chapter 4: Operation
1
Sensitivity
(nm)
400 – 1000
900 – 1600
150 – 550
800 – 1800
1200 – 2600
is the sum of the
D
∗
Cost
Low
Low
Med
Med
High
). The
s
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