THORLABS PDAPC2 User manual

PDAPC2
Si Switchable Gain
Photodetector,
OEM Package
User Guide

Si Switchable Gain Detector, OEM
Table of Contents
Chapter 1Warning Symbol Definitions ...........................................1
Chapter 2Description........................................................................2
Chapter 3Setup.................................................................................. 3
Chapter 4Operation...........................................................................8
4.1.TheoryofOperation.......................................................8
4.2.Responsivity..................................................................8
4.3.DarkCurrent..................................................................8
4.4.BandwidthandResponse...............................................9
4.5.TerminatingResistance..................................................9
4.6.GainAdjustment............................................................9
Chapter 5Troubleshooting .............................................................10
Chapter 6Specifications .................................................................11
6.1.ResponseCurve............................................................12
6.2.MechanicalDrawing....................................................13
Chapter 7Regulatory....................................................................... 14
Chapter 8Thorlabs Worldwide Contacts.......................................15

Si Switchable Gain Detector, OEM Chapter 1: Warning Symbol Definitions
Rev B, June 15, 2021 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, OEM Chapter 2: Description
Page 2 TTN235960-D02
Chapter 2 Description
The PDAPC2 is an amplified, switchable-gain, silicon (Si) photodetector in an OEM
package with an operating wavelength range of 320 to 1100 nm. A DIP switch
allows the user to vary the gain in 10 dB steps. A buffered output drives 50 Ωload
impedances up to 5 V. The output signal is readable from the MMCX connector.
We provide MMCX to BNC cables (Item # CA3339) or MMCX to SMA cables
(Item # CA3439). Users can also access the digital pins of the gain switch or the
output through an on-board header.
ESD Caution
This product is ESD sensitive. Take all appropriate precautions to
discharge personnel and equipment before making any electrical
connections to the unit.

Si Switchable Gain Detector, OEM Chapter 3: Setup
Rev B, June 15, 2021 Page 3
Chapter 3 Setup
1. The pin out table for the on-board header (J2), Figure 1, is shown in the
two tables below:
Figure 1 J2 Header
J2 PIN OUT
Pin Designation Pin Designation
1 +V 2 GND
3 GND 4 OUTPUT
5 -V 6 N.C.
7 A2 8 A1
9 A0 10 N.C.
Note:
Pins 1 & 5: ±V refers to the power supply positive/negative voltages.
Pins 7, 8, & 9: A0-A2 refers to the three digital pins for the gain adjustment.
Gain Switch Table
A2 A1 A0 Gain
0 0 0 0 dB
0 0 1 10 dB
0 1 0 20 dB
0 1 1 30 dB
1 0 0 40 dB
1 0 1 50 dB
1 1 0 60 dB
1 1 1 70 dB
Pin 10
Pin 1

Si Switchable Gain Detector, OEM Chapter 3: Setup
Page 4 TTN235960-D02
2. Connect a power supply to pins 1, 3, and 5 of the J2 header. The required
power supply voltages are:
J2 Pin Voltage
1 +12 VDC
3 GND
5 -12 VDC
Thorlabs offers the LD1255-SUPPLY as one compatible power supply
option. Connection to the board is shown below:
Figure 2 Power Supply Connection

Si Switchable Gain Detector, OEM Chapter 3: Setup
Rev B, June 15, 2021 Page 5
3. Digital gain can be adjusted through the J2 header shown in Figure 1 or
using the on-board DIP switch shown below. Each switch is ‘Off’/0 when
in the up position and ‘On’/1 when in the down position.
Figure 3 Location of the On-Board DIP Switches
The following table describes what each switch does:
Switch Number Function
1 Enable
2 A0
3 A1
4 A2
To enable the DIP switch settings, set switch # 1 to ‘On’/1. See the table
on page 3 for the corresponding gain settings.
Note: The default DIP switch settings are all in the ‘Off’/0 position and
customer could only use J2 Header for gain setting purposes. When the
DIP switch is enabled, it would override the seetings of the J2 Header.
On-Board DIP
Switches

Si Switchable Gain Detector, OEM Chapter 3: Setup
Page 6 TTN235960-D02
4. The side adjusted potentiometer is used to adjust the voltage output’s
offset at high gain settings (e.g. 70 dB). This part is factory pre-adjusted
so normally the user does not need to adjust it. However, if the output
offset value has fallen out of spec, for example drift over time or
temperature, then it is possible to adjust it back by turning this
potentiometer. Turning the screw head clockwise decreases the offset
voltage and adjusting the screw head conterclockwise increases it.
Figure 4 Side adjusted potentiometer
5. Attach a 50 Ωcoax cable to the output of the PDAPC2 detector. Thorlabs
offers two suitable cable options, the CA3339 MMCX to BNC cable or the
CA3439 MMCX to SMA cable.
When running cable lengths longer than 12", Thorlabs recommends
terminating the opposite end of the coax with a 50 Ωresistor for optimal
performance. Thorlabs Item # T4119 is suitable for this purpose.
Potentiometer
Adjustment
Screw Head
MMCX
Connector

Si Switchable Gain Detector, OEM Chapter 3: Setup
Rev B, June 15, 2021 Page 7
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 Ω.
In this case, do not install a 50 Ωterminator. The combined
loads will equal 25 Ωwhich could allow ~135 mA of output
current. This will damage the output driver of the PDA.
6. Power the PDAPC2 on. When the unit is on, the power indicator LED will
be illuminated yellow. If the LED is green or red, this indicates only one
power rail, either positive or negative, respectively, is connected. In that
case, the user would need to check the power inputs to make sure both
power rails are on and connected correctly.
7. Apply a light source to the detector, then adjust the gain controls to the
desired setting.
8. During alignment, the user should take appropriate precautions. For
example, ensuring the incident power is within safe operating power.
Additionally, the user should have proper eye and skin protection as
recommended by the light source manufacturer.

Si Switchable Gain Detector, OEM Chapter 4: Operation
Page 8 TTN235960-D02
Chapter 4 Operation
4.1. Theory of Operation
Thorlabs PDA series are ideal for measuring both pulsed and CW light sources.
The PDAPC2 includes a reverse-biased PIN photodiode, 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:
𝑅󰇛𝜆󰇜𝐼
𝑃
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, OEM Chapter 4: Operation
Rev B, June 15, 2021 Page 9
Material Dark Current Speed Sensitivity1Cost
Silicon (Si) Low High 400 - 1000 nm Low
Germanium (Ge) High Low 900 - 1600 nm Low
Gallium Phosphide (GaP) Low High 150 - 550 nm Med
Indium Gallium Arsenide
(InGaAs) Low High 800 - 1800 nm Med
Extended Range: Indium
Gallium Arsenide (InGaAs) High High 1200 - 2600 nm 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:
𝑓󰇛3𝑑𝐵󰇜𝐺𝐵𝑃
4𝜋𝑅𝐶
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 PDAPC2 is 10 V for high impedance loads (i.e. RLoad
> 5 kΩ) and 5 V for 50 Ωloads. Adjust the gain so that the measured signal level
out of the PDAPC2 is below 10 V (5 V with a 50 Ωload) to avoid saturation.
For low terminating resistors, <5 kΩor 1% error, an additional factor needs to be
considered. The output of the PDA includes a 50 Ωseries resistor (Rs). The output
load creates a voltage divider with the 50 Ωseries resistor as follows:
𝑆𝑐𝑎𝑙𝑒𝐹𝑎𝑐𝑡𝑜𝑟 𝑅
𝑅𝑅
𝑉  
󰇛𝜆󰇜∗𝑇𝑟𝑎𝑛𝑠𝑖𝑚𝑝𝑒𝑑𝑎𝑛𝑐𝑒𝐺𝑎𝑖𝑛∗𝑆𝑐𝑎𝑙𝑒𝐹𝑎𝑐𝑡𝑜𝑟∗𝐼𝑛𝑝𝑢𝑡𝑃𝑜𝑤𝑒𝑟󰇛𝑊󰇜
Note that we already include the scale factor in our specification for the gain at
50 Ω. Refer to the table in Chapter 6 for additional performance specifications.
4.6. Gain Adjustment
The PDAPC2 includes a low noise, low offset, high gain transimpedance amplifier
that allows gain adjustment over a 70 dB range. The gain is adjusted by selecting
the correct gain switch settings (see page 3). 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 11 to choose the best
gain versus bandwidth for a given input signal.
1Approximate values; actual wavelength values will vary.

Si Switchable Gain Detector, OEM Chapter 5: Troubleshooting
Page 10 TTN235960-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 specification in the
table on page 11.

Si Switchable Gain Detector, OEM Chapter 6: Specifications
Rev B, June 15, 2021 Page 11
Chapter 6 Specifications
All performance specifications are typical, performed at 25 °C ambient
temperature, and assume a 50 Ωload, 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%
Bandwidth311 MHz Bandwidth3 90 kHz
Noise (RMS) 268 μV Noise (RMS) 229 μV
NEP (@ p) 7.17 x 10-11 W/Hz NEP (@ p) 2.67 x 10-12 W/Hz
Offset ±8 mV (Typ.)
±12 mV (Max) Offset ±8 mV (Typ.) ±12 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%
Bandwidth31.4 MHz Bandwidth328 kHz
Noise (RMS) 195 μV Noise (RMS) 271 μV
NEP (@ p) 6.75 x 10-12 W/Hz NEP (@ p) 4.2 x 10-12 W/Hz
Offset ±8 mV (Typ.)
±12 mV (Max) Offset ±8 mV (Typ.) ±12 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%
Bandwidth3800 kHz Bandwidth39 kHz
Noise (RMS) 219 μV Noise (RMS) 423 μV
NEP (@ p) 3.36 x 10-12 W/Hz NEP (@ p) 6.24 x 10-12 W/Hz
Offset ±8 mV (Typ.)
±12 mV (Max) Offset: ±8 mV (Typ.) ±12 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) 222 μV Noise (RMS) 1.22 mV
NEP (@ p) 2.83 x 10-12 W/Hz NEP (@ p) 7.88 x 10-12 W/Hz
Offset ±8 mV (Typ.)
±12 mV (Max) Offset ±8 mV (Typ.) ±12 mV (Max)
2The PDAPC2 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, OEM Chapter 6: Specifications
Page 12 TTN235960-D02
Electrical Specifications
Detector - Si
Active Area - 10 mm x 10 mm (100 mm2)
Wavelength Range λ320 to 1100 nm
Peak Wavelength λp 960 nm (Typ.)
Peak Response ( λp) 0.72 A/W (Typ.)
Amplifier GBP - 600 MHz
Output Impedance - 50 Ω
Max Ouput Current IOUT 100 mA
Load Impedance - 50 Ωto 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 Ω)
0 to 10 V (Hi-Z)
General
PCB Size 1.47" x 1.47"
(37.34 mm x 37.34 mm)
Operating Temperature 10 to 40 °C
Storage Temperature -20 to 70 °C
6.1. Response Curve
400 500 600 700 800 900 1000300 1100
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
PDAPC2 Responsivity
Responsivity (A/W)
Wavelength (nm)

Si Switchable Gain Detector, OEM Chapter 6: Specifications
Rev B, June 15, 2021 Page 13
6.2. Mechanical Drawing

Si Switchable Gain Detector, OEM Chapter 7: Regulatory
Page 14 TTN235960-D02
Chapter 7 Regulatory
As required by the WEEE (Waste Electrical and Electronic Equipment Directive)
of the European Community and the corresponding national laws, Thorlabs offers
all end users in the EC the possibility to return “end of life” units without incurring
disposal charges.
This offer is valid for Thorlabs electrical and electronic equipment:
Sold after August 13, 2005
Marked correspondingly with the crossed out
“wheelie bin” logo (see right)
Sold to a company or institute within the EC
Currently owned by a company or institute within the
EC
Still complete, not disassembled and not
contaminated
As the WEEE directive applies to self contained operational electrical and
electronic products, this end of life take back service does not refer to other
Thorlabs products, such as:
Pure OEM products, that means assemblies to be built into a unit by the
user (e.g. OEM laser driver cards)
Components
Mechanics and optics
Left over parts of units disassembled by the user (PCB’s, housings etc.).
If you wish to return a Thorlabs unit for waste recovery, please contact Thorlabs or
your nearest dealer for further information.
Waste Treatment is Your Own Responsibility
If you do not return an “end of life” unit to Thorlabs, you must hand it to a company
specialized in waste recovery. Do not dispose of the unit in a litter bin or at a public
waste disposal site.
Ecological Background
It is well known that WEEE pollutes the environment by releasing toxic products
during decomposition. The aim of the European RoHS directive is to reduce the
content of toxic substances in electronic products in the future.
The intent of the WEEE directive is to enforce the recycling of WEEE. A controlled
recycling of end of life products will thereby avoid negative impacts on the
environment.

Si Switchable Gain Detector, OEM Chapter 8: Thorlabs Worldwide Contacts
Rev B, June 15, 2021 Page 15
Chapter 8 Thorlabs Worldwide Contacts
For technical support or sales inquiries, please visit us at
www.thorlabs.com/contact for our most up-to-date contact information.
USA, Canada, and South America
Thorlabs, Inc.
[email protected]
[email protected]
UK and Ireland
Thorlabs Ltd.
[email protected]
[email protected]
Europe
Thorlabs GmbH
[email protected]
Scandinavia
Thorlabs Sweden AB
[e-mail]
France
Thorlabs SAS
[email protected]
Brazil
Thorlabs Vendas de Fotônicos Ltda.
[email protected]
Japan
Thorlabs Japan, Inc.
[email protected]
China
Thorlabs China
[email protected]

Si Switchable Gain Detector, OEM Chapter 8: Thorlabs Worldwide Contacts
Rev B, June 15, 2021 Page 16
www.thorlabs.com