Dark Charge; Saturation - Teledyne NIRvana System Manual

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8.8

Dark Charge

Dark charge (also known as dark current) is the thermally induced buildup of charge in
the sensor over time. The statistical noise associated with this charge is known as dark
noise. Dark charge values vary widely from one sensor to another and are temperature
dependent.
With the light into the camera completely blocked, the sensor pixels accumulate
thermally generated electrons, dependent on the exposure time and camera
temperature. The longer the exposure time and the warmer the camera, the less
uniform this background will appear. Thus, to minimize dark-charge effects, the camera
should be operated at its default sensor temperature.
8.9

Saturation

When signal levels in a region of the image are very high, charge generated in one pixel
may exceed the "well capacity" of the pixel, spilling over into adjacent pixels in a
process called "blooming." In this case, a shorter exposure time is advisable, with signal
averaging to enhance Signal-to-Noise (S/N) Ratio accomplished through the software.
For signal levels low enough to be read-noise limited, longer exposure times, and
therefore longer signal integration on the sensor, will improve the S/N Ratio
approximately linearly with the length of exposure time. There is, however, a maximum
time limit for on-chip accumulation which is determined by either the saturation of the
sensor by the signal or the loss of dynamic range due to the buildup of dark signal.
NIRvana System Manual
NOTE:
Do not be concerned about the DC level of this background.
This is not noise. It is a fully subtractable bias pattern. Simply
acquire and save a dark charge "background image" under
conditions identical to those used to acquire the "actual"
image. Subtracting the background image from the actual
image will significantly reduce dark-charge effects.
!
CAUTION!
If a sudden change is observed in the baseline signal, there
may be excessive humidity in the camera vacuum enclosure.
Turn off the camera and contact Teledyne Princeton
Instruments Customer Support. Refer to
Information on page 124 for complete contact information.
Contact
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