CHEETAH Hardware User’s Manual
Imperx, Inc.
Rev. 6.2
6421 Congress Ave.
7/7/2015
Boca Raton, FL 33487
+1 (561) 989-0006
48 of 152
duration of the trigger pulse as shown in Figure 2.6b. The minimum exposure time
using the trigger pulse width is 2 micro-seconds. Upon completing the readout, the
trigger cycle is completed and the camera idles awaiting the next trigger pulse.
RS Mode:
With limitations, the exposure time can be controlled using trigger pulse
width.. In this case, the minimum exposure time is equal to the time required to reset
all the rows within the image sensor (the time readout one frame of the image
sensor). In other words, the minimum exposure time is equal to the frame time.
Longer exposure times are possible, but exposures shorter than one frame time are
not supported.
Upon receiving the active edge of the trigger signal, the camera resets image sensor
row #1 and exposure of line #1 begins. One row time later, row #2 is reset and the
integration of row #2 begins. Each row is reset one line time after the prior row and
this process continues until the entire image sensor is reset. When the trigger signal
goes inactive (must be one frame time min. later), the integration concludes for the
first row and the image sensor is readout one line at a time. The time between trigger
pulses (start of exposure) must be at least the exposure time plus the readout time of
the image sensor.
It is possible to use strobed illumination in rolling shutter mode, if the scene is
completely dark. In RS mode, the flash must occur after all the rows within the
image sensor have been reset (one frame readout time) and the exposure time must
therefore be set to the sum of the image sensor readout time plus the exposure
window for the flash. The sequence is as follows: the exposure starts and all rows in
the image sensor are reset (one frame time), the strobe illumination flashes, the
exposure ends and the readout begins. Once the readout has completed, the next
exposure can begin.
Figure 2.6a Standard Trigger Mode (Internal Exposure Control)