THORLABS PDB440A, Руководство по эксплуатации, Страница: 15 / 29

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5 Appendix
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5 Appendix
Comments and explanations to the individual specifications
- Typical max. responsivity is the peak responsivity
Â
(l)
max
of the photo diode.
- Transimpedance Gain [V/A] is the ratio of the output voltage to the photo current:
As the photo current depends on the wavelength, the transimpedance gain is wavelength-
independent as well. The transimpedance gain values are always given for a high imped-
ance load at the RF Output; for 50
W
loads these values are divided by two.
-
Conversion Gain [V/W] is the ratio of output voltage to input optical power:
This formula shows, that the conversion gain is dependent on the actual wavelength, as
well. In the specifications, the conversion gain is given only for the peak responsivity
wavelength of the photo diode. The conversion gain values are always given for a high im-
pedance load at the RF Output; for 50
W
loads these values are divided by two..
- NEP (Noise Equivalent Power) is the minimum input optical power to generate a photo cur-
rent, equal to the RMS noise current in a 1 Hz bandwidth. NEP is essentially the minimum
detectable power. It is stated for the PDB440x and PDB450x detectors balanced detectors
from DC to the RF Output cut frequency.
- Max. input power is the damage threshold of the photo diode.
- Typical noise spectra (diagrams): These spectra were measured using an electrical spec-
trum analyzer (resolution bandwidth 100 kHz, video bandwidth 10 kHz unless otherwise
noted). The INPUTs of the balanced detectors under test were blocked. The lower curve in
the diagram was measured with the same setup and the balanced detectors under test
switched off , i.e., it represents the measurement system’s noise floor.
- Monitor outputs are designed for use with high impedance loads (e.g., high-Z scope input
etc.), but can also drive 50 W loads. Monitor outputs conversion gain is 10 V/mW, given at
the detectors peak responsivity and high impedance load.
- Typical frequency response curves are measured using the setup described in section
"CMRR and Frequency Response"
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