THORLABS PDA015AM, Руководство пользователя

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Si Amplified Photodetectors Chapter 5: Operation
Page 8 TTN112567-D02
Chapter 5 Operation
5.1. Theory of Operation
Thorlabs’ PDA015A is ideal for measuring both modulated/pulsed and CW light
sources. As is shown in Figure 2, the PDA015A includes a reverse-biased PIN
photodiode (PD) mated to a fixed gain transimpedance amplifier (TIA) followed by
a buffer amplifier, and packaged in a rugged housing. The photodiode generates
a current in response to the optical input which is then converted to a voltage and
amplified by the TIA. The Buffer Amplifier adds yet another level of gain. Note that
the output is passed through a 50
Ω series resistor before reaching the output
connector. The user can apply either a 50 Ω or high-impedance external load
depending on the situation.
Figure 2. Block Diagram of the PDA015A Amplified Si Photodetector
5.2. Responsivity and Dark Current
The responsivity of a photodiode can be defined as a ratio of generated
photocurrent (I
PD
) to the incident light power (P) at a given wavelength (in units of
A/W):

λ
The dark current is defined as the current from the photodiode when no light is
applied. Depending on the photodiode size, material, and reverse-bias voltage, the
dark current can range from less than a nA up to many
μ A. In the case of the
PDA015A, in most cases the dark current is small enough to ignore (<3 nA).
Note that the PDA015A also has a dark output voltage (see specifications in
Chapter 7), which is dominated by the input offset voltage error of the TIA. This is
significantly larger that any contribution due to the PD dark current.
PD
TIA Buffer 50
Ω
R
S
R
Load
50
Ω
to Hi-Z
Input
External Load