THORLABS PDAPC1 User manual

PDAPC1

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 A, April 5, 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 TTN235959-D02

Chapter 2 Description

The PDAPC1 is an amplified, switchable-gain, silicon (Si) photodetector in an OEM

package with an operating wavelength range of 350 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 A, April 5, 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

Designation

GND

OUTPUT

-V

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

Gain

0 dB

10 dB

20 dB

30 dB

40 dB

50 dB

60 dB

70 dB

Pin 10

Pin 1

Si Switchable Gain Detector, OEM Chapter 3: Setup

Page 4 TTN235959-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

+12 VDC

GND

-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 A, April 5, 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

Enable

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 TTN235959-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 PDAPC1 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 A, April 5, 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 PDAPC1 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 TTN235959-D02

Chapter 4 Operation

4.1. Theory of Operation

Thorlabs PDA series are ideal for measuring both pulsed and CW light sources.

The PDAPC1 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:

󰇛󰇜



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.

Table of contents

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