Teledyne Princeton Instruments NIRvana HS, Системное руководство

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Chapter 7: Exposure
This chapter discusses factors that affect exposure and the accumulation of charge on
the FPA sensor.
A Focal Plane Array (FPA) such as the one in NIRvana HS is a matrix of photodiodes
bonded to a readout circuit on an IC chip. The photodiodes are sensitive to NIR
wavelengths in which they absorb NIR radiation, convert it into electrons, and send a
voltage signal in response to form an image. NIR imaging FPA photodiodes are
composed of materials sensitive to NIR radiation.
Each cell on an FPA is connected to its own charge storage well. These cells respond to
the intensity of light or NIR radiation falling on their collection areas and store a
proportional amount of charge in their associated wells. Once charge accumulates for
the specified Exposure Time the charge in each well is read out serially through four
video output ports.
REFERENCES:
Refer to Chapter 8, Readout , on page 53 for complete
information.
7.1 Exposure Time
Exposure Time is configured in LightField on the Common Acquisition Settings
expander and is the time between commands sent to start and stop signal
accumulation on the sensor.
7.2 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.