Version 1.0 rev 14 Aug 2019
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4.10.1
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Global Shutter can also be thought of as a ‘snapshot’ exposure mode, meaning that all pixels of the array are exposed
simultaneously. Before the exposure begins, all pixels in the array are cleared of charge using the Global Clear. At the
start of the exposure each pixel simultaneously begins to collect charge and is allowed to do so for the duration of
the exposure time. At the end of exposure, all pixels transfer their accumulated charge simultaneously to their read
out node. In order to obtain a low read noise Global Shutter requires a reference frame to be read out of the sensor in
addition to the signal frame, this effectively halves the frame rate that could have been achieved in Rolling Shutter mode.
4.10.2
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The Global Shutter signals shown in the diagrams are as follows:
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EXT/SW Trigger:
Represents an external TTL trigger supplied to the camera or a trigger command sent via
software in response to a user action (e.g. a button press).
•
FIRE
: In Global Shutter mode, the FIRE output indicates the exposure period, which is identical for all pixels.
This pulse is available to the user via the FIRE output pin.
NOTE: In Global Shutter Mode the behaviour of
FIRE Row N, FIRE ALL and FIRE ANY are identical to that of FIRE and therefore not shown in the diagrams.
•
ARM
: The ARM output from the camera is used for external and software triggering modes to indicate when the
camera is ready to accept another incoming trigger pulse.
Additional signal to aid end user understanding:
•
Global Clear
: Global Shutter uses Global Clear to begin a new exposure. When this pulse is HIGH, charge is
drained from every pixel thus preventing the accumulation of charge on the sensor. When the pulse is LOW,
any photo-electrons generated are accumulating within the pixels, ready for transfer to the sense node for
subsequent readout. The falling edge indicates the start of an exposure.
•
Charge Transfer
: This signal indicates when charge in the pixel is transferred to the measurement node and
effectively ends the exposure. The charge is transferred while the pulse is HIGH and is shown in the diagrams
to indicate there is a specified time between reading out the reference and signal frames.
•
Frame Read Out Phase
: This signal indicates when reference and signal frames are read out of the sensor.
•
: Marks the start of an exposure.
•
: Marks the end of an exposure.
