9
If subsequent trigger pulses occur faster than the combined exposure and readout time,
any trigger received during the exposure or readout time will be ignored, as illustrated in
appendix A.
Exposure range (full-resolution— without binning or Region-of Interest):
20MHz Single-Tap Readout:
Increments of 111.5 microseconds, ranging from 111.5
microseconds to 2 hours.
20MHz Dual-Tap Readout:
Increments of 60 microseconds, ranging from 60
microseconds to 1 hour.
40MHz Single-Tap Readout:
Increments of 58.5 microseconds, ranging from 58.5
microseconds to 1 hour.
40MHz Dual-Tap Readout:
Increments of 33 microseconds, ranging from 33
microseconds to 35 minutes.
5.2.4.
Bulb (pulse-width exposure) mode
The term “bulb” mode is borrowed from photography, denoting a camera setting in
which the shutter stays open as long as the shutter button is depressed. Bulb mode in the
DVC-4000D is analogous in that the CCD exposes as long as the trigger signal is
asserted (a low logic level on the external trigger or a low command on the Camera Link
CC1 control line). Upon the rising edge of the trigger signal, readout of the exposure is
initiated. Maximum exposure time is indefinite, although dark current will set the
practical exposure time limit, depending on the operating temperature and the tolerance
of the application to dark current pattern noise.
Exposure range:
20MHz or 40MHz Readout:
5 microseconds minimum. Maximum limited by dark
current and particular application.
5.3.
Binning
Binning is the process of summing adjacent lines and/or pixels in order to increase dynamic
range, sensitivity, or both. Binning can either be accomplished on the CCD itself by summing
the collected charge (on-chip binning) or in software, after A/D conversion. On-chip binning can
result in slightly lower noise relative to software binning, under certain circumstances. Because
fewer lines are actually read out when binning vertically, on-chip binning in the vertical
direction can produce a significant increase in frame rate with increasing binning ratios.
However, because the clocking cannot be accelerated in the horizontal direction, horizontal
binning provides no such speed increase.
In all modes of operation, the DVC-4000D 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, anti-blooming 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