THORLABS PDA36A2 User manual

PDA36A2
Si Switchable Gain
Detector
User Guide

Si Switchable Gain Detector
Table of Contents
Chapter 1Warning Symbol Definitions ...........................................1
Chapter 2Description........................................................................2
Chapter 3Setup.................................................................................. 3
Chapter 4Operation...........................................................................4
4.1.TheoryofOperation.......................................................4
4.2.Responsivity..................................................................4
4.3.DarkCurrent..................................................................4
4.4.BandwidthandResponse...............................................5
4.5.TerminatingResistance..................................................5
4.6.GainAdjustment............................................................5
Chapter 5Troubleshooting ...............................................................6
Chapter 6Specifications ...................................................................7
6.1.ResponseCurve..............................................................9
6.2.MechanicalDrawing....................................................10
Chapter 7Certificate of Conformance ...........................................11
Chapter 8Regulatory.......................................................................12
8.1.WasteTreatmentisYourOwnResponsibility...............12
8.2.EcologicalBackground.................................................12
Chapter 9Thorlabs Worldwide Contacts.......................................13

Si Switchable Gain Detector Chapter 1: Warning Symbol Definitions
Rev A, December 27, 2017 Page 1
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on your
device.
Symbol Description
Direct Current
Alternating Current
Both Direct and Alternating Current
Earth Ground Terminal
Protective Conductor Terminal
Frame or chassis Terminal
Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution, Risk of Electric Shock
Caution, Hot Surface
Caution, Risk of Danger
Warning, Laser Radiation
Caution: ESD Sensitive Components

Si Switchable Gain Detector Chapter 2: Description
Page 2 TTN135069-D02
Chapter 2 Description
The PDA36A2 is an amplified, switchable-gain, Silicon (Si) detector designed for
detection of light signals ranging from 350 to 1100 nm. An eight-position rotary
switch allows the user to vary the gain in 10 dB steps. A buffered output drives
50 load impedances up to 5 V. The PDA36A2 housing includes a removable
threaded coupler (SM1T1) and retainer ring (SM1RR) that is compatible with any
number of Thorlabs 1" threaded accessories. This allows convenient mounting of
external optics, light filters, apertures, as well as providing an easy mounting
mechanism using Thorlabs’ cage assembly accessories.
ESD Caution
The components inside this instrument are ESD sensitive. Take all
appropriate precautions to discharge personnel and equipment before
making any electrical connections to the unit.

Si Switchable Gain Detector Chapter 3: Setup
Rev A, December 27, 2017 Page 3
Chapter 3 Setup
The detector can be set up in many different ways using our extensive line of
adapters. However, the detector should always be mounted and secured for best
operation.
1. Unpack the optical head, install a Thorlabs TR-series Ø1/2" or Ø25 mm
post into one of the mounting holes, located on the bottom and side of
the sensor, and mount using a PH-series post holder. Note that these
detectors feature tapped holes that accept both 8-32 and M4 threads,
so using either imperial or metric TR posts is possible.
2. Connect the power supply 3-pin plug into the power receptacle on the
PDA36A2.
3. Plug the power supply into a 50 to 60Hz, 100 V / 120 V / 230 V power
outlet.
4. Attach a 50 coax cable (i.e. RG-58U) to the output of the PDA. When
running cable lengths longer than 12" we recommend terminating the
opposite end of the coax with a 50 resistor (Thorlabs p/n T4119) for
maximum performance. Connect the remaining end to a measurement
device such as an oscilloscope or high speed DAQ card. Caution: Many
high speed oscilloscopes have input impedances of 50 . In this case,
do not install a 50 terminator. The combined loads will equal 25 
which could allow ~135 mA of output current. This will damage the
output driver of the PDA36A2.
5. Power the PDA36A2 on using the power switch located on the top side
of the unit.
Caution!
The PDA36A2 was designed to allow maximum accessibility to the
photodetector by having the active area surface of the diode flush with the
outside of the PDA housing. When using fiber adapters, make sure that the
fiber ferrule does not crash into the detector. Failure to do so may cause
damage to the diode and or the fiber.
6. Install any desired filters, optics, adapters, or fiber adapters to the input
aperture.
7. During alignment, take appropriate precautions, such as using reduced
radiation power, or other precautions, and use proper eye and/or skin
protection as recommended by the radiation source manufacturer.
8. Apply a light source to the detector. Adjust the gain to the desired
setting.
!!

Si Switchable Gain Detector Chapter 4: Operation
Page 4 TTN135069-D02
Chapter 4 Operation
4.1. Theory of Operation
Thorlabs PDA series are ideal for measuring both pulsed and CW light sources.
The PDA36A2 includes a reverse-biased PIN photo diode, mated to a switchable
gain transimpedance amplifier, and packaged in a rugged housing.
4.2. Responsivity
The responsivity of a photodiode can be defined as a ratio of generated
photocurrent (IPD) to the incident light power (P) at a given wavelength:
󰇛󰇜

4.3. Dark Current
Dark current is leakage current which flows when a bias voltage is applied to a
photodiode. The PDA with Transimpedance Amplifier does control the dark
current flowing out. Looking at the figure above, it can be noted that Point B is
held at ground and the amplifier will try to hold point A to “Virtual Ground”. This
minimizes the effects of dark current present in the system.
The dark current present is also affected by the photodiode material and the size
of the active area. Silicon devices generally produce low dark current compared
to germanium devices which have high dark currents. The table below lists
several photodiode materials and their relative dark currents, speeds, sensitivity,
and costs. Please note that sensitivity values in the table are typical values;
Thorlabs offers photodetectors with sensitivity ranges that vary from those shown
below.
Photodetector
Transimpedance Amp
Out
Feedback
R
F
A
B
-V
BNC
GND
GND GND
R
LOAD

Si Switchable Gain Detector Chapter 4: Operation
Rev A, December 27, 2017 Page 5
Material Dark
Current Speed Sensitivity1 (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 (Rf). The bandwidth of the detector can be calculated using the
following:
󰇛3󰇜
4
Where GBP is the amplifier gain bandwidth product and CDis 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) and 5 V for 50 loads. Adjust the gain so that the measured
signal level out of the PDA36A2 is below 10 V (5 V with a 50 load) to avoid
saturation.
For low terminating resistors, <5 kor 1% error, an additional factor needs to be
considered. The output of the PDA includes a 50 series resistor (Rs). The
output load creates a voltage divider with the 50 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.
1Approximate values; actual wavelength values will vary.

Si Switchable Gain Detector Chapter 5: Troubleshooting
Page 6 TTN135069-D02
Chapter 5 Troubleshooting
Problem Suggested Solutions
There is no signal response.
Verify that the power is switched on and all
connections are secure.
Verify the proper terminating resistor is installed if
using a Voltage measurement device.
Verify that the optical signal wavelength is within
the specified wavelength range.
Verify that the optical signal is illuminating the
detector active area.
Output Voltage will not increase.
Detector Output is skewed.
Check to make sure the detector is not saturated.
Refer to the Output Voltage spec. in the
Specifications table.
Install a 1" Lens Tube (SM1L10) to the thread
coulpler (SM1T1) to baffle any external light
sources to see if this improves the response.

Si Switchable Gain Detector Chapter 6: Specifications
Rev A, December 27, 2017 Page 7
Chapter 6 Specifications
All performance specifications are typical, performed at 25 °C ambient
temperature, and assume a 50 load, unless stated otherwise.
Performance Specifications2
0 dB Setting 40 dB Setting
Gain (Hi-Z) 1.51 x 103V/A ±2% Gain (Hi-Z) 1.51 x 105V/A ±2%
Gain (50 Ω) 0.75 x 103V/A ±2% Gain (50 Ω) 0.75 x 105V/A ±2%
Bandwidth312 MHz Bandwidth3 90 kHz
Noise (RMS) 258 V Noise (RMS) 214 V
NEP (@ p) 7.57 x 10-11 W/Hz NEP (@ p) 3.25 x 10-12 W/Hz
Offset ±5 mV (Typ.)
±10 mV (Max) Offset ±6 mV (Typ.) ±10 mV (Max)
10 dB Setting 50 dB Setting
Gain (Hi-Z) 4.75 x 103V/A ±2% Gain (Hi-Z) 4.75 x 105V/A ±2%
Gain (50 Ω) 2.38 x 103V/A ±2% Gain (50 Ω) 2.38 x 105V/A ±2%
Bandwidth31.6 MHz Bandwidth328 kHz
Noise (RMS) 192 V Noise (RMS) 234 V
NEP (@ p) 5.8 x 10-12 W/Hz NEP (@ p) 3.69 x 10-12 W/Hz
Offset ±6 mV (Typ.)
±10 mV (Max) Offset ±6 mV (Typ.)
±10 mV (Max)
20 dB Setting 60 dB Setting
Gain (Hi-Z) 1.5 x 104V/A ±2% Gain (Hi-Z) 1.5 x 106V/A ±5%
Gain (50 Ω) 0.75 x 104V/A ±2% Gain (50 Ω) 0.75 x 106V/A ±5%
Bandwidth31 MHz Bandwidth39 kHz
Noise (RMS) 207 V Noise (RMS) 277 V
NEP (@ p) 3.4 x 10-12 W/Hz NEP (@ p) 4 x 10-12 W/Hz
Offset ±6 mV (Typ.)
±10 mV (Max) Offset: ±6 mV (Typ.) ±10 mV (Max)
30 dB Setting 70 dB Setting
Gain (Hi-Z) 4.75 x 104V/A ±2% Gain (Hi-Z) 4.75 x 106V/A ±5%
Gain (50 Ω) 2.38 x 104V/A ±2% Gain (50 Ω) 2.38 x 106V/A ±5%
Bandwidth3260 kHz Bandwidth33 kHz
Noise (RMS) 211 V Noise (RMS) 388 V
NEP (@ p) 3.4 x 10-12 W/Hz NEP (@ p) 4.29 x 10-12 W/Hz
Offset ±6 mV (Typ.)
±10 mV (Max) Offset ±8 mV (Typ.) ±12 mV (Max)
2The PDA36A2 has a 50 Ωseries terminator resistor (i.e. in series with amplifier output). This
forms a voltage divider with any load impedance (e.g. 50 Ωload divides signal in half).
3Tested at 650 nm wavelength. For NIR wavelengths, the rise time of the photodiode element will
become slower which may limit the effective bandwidth of the amplified detector.

Si Switchable Gain Detector Chapter 6: Specifications
Page 8 TTN135069-D02
Electrical Specifications
Detector - Si
Active Area - 3.6 mm x 3.6 mm (13 mm2)
Wavelength Range 350 to 1100 nm
Peak Wavelength p 970 nm (Typ.)
Peak Response ( p) 0.65 A/W (Typ.)
Amplifier GBP - 600 MHz
Output Impedance - 50 
Max Ouput Current IOUT 100 mA
Load Impedance - 50 to Hi-Z
Gain Adjustment Range - 0 dB to 70 dB
Gain Steps - 8 x 10 dB Steps
Output Voltage VOUT 0 to 5 V (50 )
0 to 10 V (Hi-Z)
General
On/Off Switch Slide
Gain Switch 8 Position Rotary
Output BNC (DC Coupled)
Package Size 2.79" x 1.96" x 0.89"
(70.9 mm x 49.8 mm x 22.5 mm)
PD Surface Depth40.09" (2.2 mm)
Weight, Detector Only 0.10 kg
Accessories SM1T1 Coupler
SM1RR Retainer Ring
Operating Temp 10 to 40 °C
Storage Temp -20 to 70 °C
AC Power Supply AC – DC Converter
Input Power531 W
100 V / 120 V / 230 V, 50 – 60 Hz
4Measured from the active area to the start of the threads on the housing body. The detector
active area surface is flush with the front of the housing body.
5Although the power supply is rated for 31 W the PDA36A2 actual usage is <5 W over the full
operating range.