Teledyne PIXIS-XF, System Manual

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62 PIXIS-XF System Manual Issue 5
6.1.3 External Sync with Continuous Cleans {Clean Until Trigger} Timing
Another timing mode available with the PIXIS-XF is Continuous Cleans {Clean Until
Trigger}. In addition to the standard cleaning of the array which occurs after the camera
is enabled, this mode removes any charge from the array until the moment the External
Sync pulse trigger edge is received. See
Figure 6-5 for a high-level block diagram of this
process.
Figure 6-5: High-Level Block Diagram: Continuous Cleans {Clean Until Trigger}
Once the External Sync pulse trigger edge is received, cleaning of the array stops as
soon as the current row is shifted, and frame collection begins. A time delay of up to
one row shift can be expected. With Normal Shutter {Normal} operation the shutter is
opened for the set exposure time. With PreOpen Shutter {Open Before Trigger}
operation the shutter is open during the continuous cleaning, and once the External
Sync pulse trigger edge is received the shutter remains open for the set exposure time,
then closes. If the vertical rows are shifted midway when the External Sync pulse trigger
edge arrives, the pulse is saved until the row shifting is completed, to prevent the CCD
from getting out of sync. As expected, the response latency is on the order of one
vertical shift time, from 1-30

s depending on the array. This latency does not prevent
the incoming signal from being detected since photo generated electrons are still
collected over the entire active area. However, if the signal arrival is coincident with the
vertical shifting, image smearing of up to one pixel is possible. The amount of smearing
is a function of the signal duration compared to the single vertical shift time.
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