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In all modes of operation, the DVC-4000 is capable of arbitrary on-chip binning (2x, 3x, 4x,
5x…21x,…) in the vertical direction, and 2x, 3x, and 4x on-chip binning in the horizontal
direction. As vertical binning increases, antiblooming control decreases, so the user must control
image illumination more carefully while binning. However, blooming does not cause any
damage to the camera.
As the binning factor increases, the CCD vertical registers are driven faster. This naturally
causes more heating of the CCD and driving electronics. Since dark current generation increases
with CCD die temperature, a noticeable increase in CCD dark current can occur at very high
binning factors.
5.4.
Region of Interest
Arbitrary, on-chip vertical Region of Interest (ROI) is fully supported on the DVC-4000
cameras. As illustrated below, when ROI is enabled, the regions above and below the region of
interest are “dumped” as fast as the CCD allows. The region of interest itself is read out
normally. Dumping unwanted lines outside the ROI can significantly increase the readout rate of
the camera. DVCView software provides interactive, graphical ROI selection, and the DVC
camera API provides developers with full ROI control. On-chip horizontal ROI is not available.
Simultaneous binning and ROI is fully supported.
As in binning, the CCD vertical registers are driven faster when the region of interest is reduced.
Dark current can increase during operation with small regions of interest.
6.
CCD phenomena
The KAI-4021 CCD is a high-performance image sensor with remarkably ideal behavior over a wide
operating range. To be as versatile as possible, the DVC-4000 camera exploits as much of the CCD
capability as possible and provides the user a great degree of control over the CCD functions. As a
result, it is possible to observe some interesting, low-level CCD phenomena under certain extreme
conditions.
6.1.
Blooming
Blooming is the result of charge spillover in the vertical transfer regions when the signal greatly
exceeds saturation. The DVC-4000 provides anti-blooming control, which suppresses blooming
under most imaging conditions. If signal levels are extreme and such high signal levels cover a
large percentage of the field of view, blooming may occur. The result is jagged, vertical bright
streaks running below such regions.
During binning, it is possible to bloom in the horizontal direction, especially when binning
greater than 4x vertically. This is because the horizontal register charge capacity is exceeded, the
KAI-4021 horizontal register has no anti-blooming capability and charge spills over during
horizontal readout. Therefore, illumination levels must be more carefully controlled as the
vertical binning factor is increased.
6.2.
Smear
Smear is inherent to interline CCD sensors such as the KAI-4021. It is the result of transferring
image charge out of the pixels and into the adjacent vertical charge-transfer registers while
photons strike the CCD. Though the vertical charge-transfer registers are covered with a light
shield, unwanted signal can be introduced into them either by small amounts of light leaking
under the light shield or by signal electrons diffusing into the transfer region from the adjacent
pixels.
