THORLABS PDA36A User manual

PDA36A(-EC)
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............................................................6
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 E, July 15, 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 13053-D04
Chapter 2 Description
The PDA36A(-EC) is an amplified, switchable-gain, silicon 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 PDA36A(-EC) 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 E, July 15, 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 ½" diameter post
into one of the #8-32 (M4 on -EC version) tapped holes, located on the
bottom and side of the head, and mount into a PH-series post holder.
2. Connect the power supply 3-pin plug into the power receptacle on the
PDA36A(-EC).
3. Plug the power supply into a 50 to 60 Hz, 100 to 120 VAC outlet (220 to
240 VAC for -EC version).
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 PDA36A(-EC).
5. Power the PDA36A(-EC) on using the power switch located on the top
side of the unit.
Caution!
The PDA36A(-EC) was designed to allow maximum accessibility to the
photodetector by having the front 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. An easy way to accomplish this is to install a
SM1RR retaining ring [included with the PDA36A(-EC)] inside the 1" threaded
coupler before installing the fiber adapter
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 13053-D04
Chapter 4 Operation
4.1. Theory of Operation
Thorlabs PDA series are ideal for measuring both pulsed and CW light sources.
The PDA36A(-EC) 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:
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
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.
Photodetector
Transimpedance Amp
Out
Feedback
R
F
A
B
-V
BNC
GND
GND GND
R
LOAD

Si Switchable Gain Detector Chapter 4: Operation
Rev E, July 15, 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
A load resistor will react with the photodetector junction capacitance to limit the
bandwidth. For best frequency response, a 50 terminator should be used in
conjunction with a 50 coaxial cable. 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
A load resistance is used to convert the generated photocurrent into a voltage
(VOUT) for viewing on an oscilloscope:
Depending on the type of the photodiode, load resistance can affect the
response speed. For maximum bandwidth, we recommend using a 50 coaxial
cable with a 50 terminating resistor at the opposite end of the cable. This will
minimize ringing by matching the cable with its characteristic impedance. If
bandwidth is not important, you may increase the amount of voltage for a given
light level by increasing RLOAD. In an unmatched termination the length of the
coaxial cable can have a profound impact on the response, so it is recommended
to keep the cable as short as possible.
The maximum output of the PDA36A(-EC) is 10 volts for high impedance loads
(i.e. RLoad > 5 k) and 5 volts for 50 loads. Adjust the gain so that the
measured signal level out of the PDA36A(-EC) is below 10 volts (5 volts with a
50 load) to avoid saturation.
For low terminating resistors, <5 kor 1% error, an additional factor needs to be
considered. As described above the output includes a 50series resistor (RS).
The output load creates a voltage divider with the 50series resistor as follows:
1Approximate values, actual wavelength values will vary from unit to unit.

Si Switchable Gain Detector Chapter 5: Troubleshooting
Page 6 13053-D04
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
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4.6. Gain Adjustment
The PDA36A(-EC) includes a low noise, low offset, high gain transimpedance
amplifier that allows gain adjustment over a 70dB 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 10dB steps. It is important to note that the
bandwidth will decrease as the gain increases. See the specifications table in
Chapter 6 to choose the best gain vs. bandwidth for a given input signal.
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 E, July 15, 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%
Bandwidth310.0 MHz Bandwidth3 150 kHz
Noise (RMS) 300 V Noise (RMS) 340 V
NEP (@ p) 2.91 x 10-11 W/Hz NEP (@ p) 5.93 x 10-13 W/Hz
Offset ±3 mV (Typ.)
±10 mV (Max) Offset ±4 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%
Bandwidth35.5 MHz Bandwidth345 kHz
Noise (RMS) 280 V Noise (RMS) 400 V
NEP (@ p) 7.52 x 10-12 W/Hz NEP (@ p) 7.94 x 10-13 W/Hz
Offset ±4 mV (Typ.)
±10 mV (Max) Offset ±4 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 (5 0Ω) 0.75 x 104V/A ±2% Gain (50 Ω) 0.75 x 106V/A ±5%
Bandwidth31.0 MHz Bandwidth311 kHz
Noise (RMS) 250 V Noise (RMS) 800 V
NEP (@ p) 2.34 x 10-12 W/Hz NEP (@ p) 1.43 x 10-12 W/Hz
Offset ±4 mV (Typ.)
±10 mV (Max) Offset: ±5 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 Bandwidth35 kHz
Noise (RMS) 260 V Noise (RMS) 1.10 mV
NEP (@ p) 1.21 x 10-12 W/Hz NEP (@ p) 2.10 x 10-12 W/Hz
Offset ±4 mV (Typ.)
±10 mV (Max) Offset ±6 mV (Typ.) ±10 mV (Max)
2The PDA36A 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).
3For 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 13053-D04
Electrical Specifications
Detector - Si PIN
Active Area - 3.6 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 10dB 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 2.76" x 2.06" x 0.88"
(70.1 mm x 52.3 mm x 22.4 mm)
PD Surface Depth 0.16" (4.1 mm)
Weight, Detector Only 0.15 lbs
Accessories SM1T1 Coupler
SM1RR Retainer Ring
Operating Temp 0 to 40 °C
Storage Temp -55 to 125 °C
AC Power Supply AC – DC Converter
Input Power4
31 W
100 – 200 VAC (50 to 60Hz)
220 – 240 VAC (50 to 60 Hz)
4Although the power supply is rated for 31 W the PDA36A actual usage is <5 W over the
full operating range.