THORLABS PDAPC2 User manual
PDAPC2
Si Switchable Gain
Photodetector,
OEM Package
User Guide
Si Switchable Gain Detector, OEM
Table of Contents
Chapter 1Warning Symbol Definitions ...........................................1
Chapter 2Description........................................................................2
Chapter 3Setup.................................................................................. 3
Chapter 4Operation...........................................................................8
4.1.TheoryofOperation.......................................................8
4.2.Responsivity..................................................................8
4.3.DarkCurrent..................................................................8
4.4.BandwidthandResponse...............................................9
4.5.TerminatingResistance..................................................9
4.6.GainAdjustment............................................................9
Chapter 5Troubleshooting .............................................................10
Chapter 6Specifications .................................................................11
6.1.ResponseCurve............................................................12
6.2.MechanicalDrawing....................................................13
Chapter 7Regulatory....................................................................... 14
Chapter 8Thorlabs 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:
𝑅𝜆𝐼
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
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