Chapter 4 Operation; Theory Of Operation; Responsivity; Dark Current - THORLABS PDA10CS User Manual

InGaAs Switchable Gain Detector

Chapter 4 Operation

4.1. Theory of Operation

Thorlabs PDA series are ideal for measuring both pulsed and CW light sources.
The PDA10CS(-EC) includes a reverse-biased PIN photo diode, mated to a
switchable gain transimpedance amplifier, and packaged in a rugged housing.
Photodetector
-V
GND

4.2. Responsivity

The responsivity of a photodiode can be defined as a ratio of generated
photocurrent (I
PD

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.
Page 4
Feedback
A
B
Transimpedance Amp
GND
) to the incident light power (P) at a given wavelength:
R
F
Out
Chapter 4: Operation
BNC
R
LOAD
GND
13058-D02