Temperature Compensation - THORLABS APD440A Operation Manual

Â
(l) for a given wavelength can be read from the typical spectral responsivity curves (see
·
M
Appendix ).
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· The M-factor (gain) adjustment range is 5 - 50 (APD440A2) and 10 - 100 (APD440A) at 23°C
ambient temperature.
· The amplifier's transimpedance gain G is 50 MV/A (High-Z termination) and 25 MV/A (50 W).
The maximum output voltage of the APD440x is 2.0 V into 50 W and 4.1 V for high impedance
loads. Depending on the wavelength, the responsivity
the amplifier will reach saturation at optical input power greater than CW Saturation Power lis-
ted in specifications. To avoid saturation, keep the output signal below the specified maximum
output voltage.
The ultra-low noise design includes an active low-pass filter to effectively suppress out-of-band
noise.
The amplifier offset voltage is factory set to zero at 23°C ambient temperature. Due to the very
high transimpedance gain, small temperature changes may affect the offset voltage. Therefore
it is recommended to use the Avalanche Photodetectors in a constant temperature environment
after a short warm up period (~5 min) for exact DC light level measurements.
Please find typical curves for
Noise Distribution
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3.5.3 Temperature Compensation

Due to internal processes, the M-factor is temperature dependent. At a fixed reverse bias
voltage the M-factor will change with temperature: with lower temperatures the M-factor will in-
crease, with higher temperatures, it will decrease.
To compensate for this effect, the Thorlabs APD440x Avalanche Photodetectors carry a ther-
mistor that senses the temperature inside the APD440x enclosure. A special electronic circuit
controls the reverse voltage applied to the APD in accordance with the temperature change.
Since the M-factor depends on the applied reverse voltage, this reduces the temperature de-
pendency of the M factor. Please see the technical data for the M-factor
ity specifications and the section
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© 2020 Thorlabs
Responsivity
and M Factor Temperature Dependency
M Factor Temperature Dependency
Â(l)
of the detector and the M factor,
, Output Frequency Response
10
13
3 Operating Instruction
and
11
in the chapter Appendix.
Temperature Stabil-
for typical curves.
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Spectral
7