9
40MHz Readout:
Increments of 58.5 microseconds, ranging from 58.5 microseconds to
3925 seconds.
5.2.4.
Edge-triggered exposure (single frame capture) mode
Edge-triggered exposure mode enables the camera to initiate an exposure immediately
upon the leading (falling) edge of the external or CameraLink control lines, with an
exposure time set by software. Alternatively, the exposure can be initiated by the host
via the DVC API. The exposure and readout sequence is the same as the non-
overlapped, continuous mode and has the same exposure range, except only one frame is
generated. Once the readout of that frame has finished, the camera returns to the armed
state, awaiting the next trigger edge.
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—no binning or ROI):
20MHz Readout:
Increments of 111.5 microseconds, ranging from 111.5 microseconds
to 7480 seconds.
40MHz Readout:
Increments of 58.5 microseconds, ranging from 58.5 microseconds to
3925 seconds.
5.2.5.
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-4000 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 CameraLink 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:
10us 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.
