Specifications

Table Of Contents
Version 1.1 rev Jan 2013
Page 71
iXon Ultra
, Features and Functionality
3.5.2.2 - External & Fast External (NFT)
In External Trigger modes, once an acquisition has been started, the camera is placed into the special clearing cycle
called “External Trigger Keep Clean’, which was discussed previously. As can be seen from the gure below, the
External Keep Clean Cycle runs continuously until the rst external trigger event is detected; at which point the current
cycle series will complete before the exposure phase starts. During the exposure there are no vertical clocks running.
There will, however, be horizontal clocks to ensure that the shift register continues to be kept clean. Once the exposure
time has elapsed the charge built up in the Image area is quickly transferred into the Storage area. From the Storage
area the charge is read out as normal. At the completion of the readout the camera restarts the External Keep Clean
Cycle.
If the camera is in Fast External Trigger mode it will accept a trigger event immediately and start the next exposure.
If, however, the camera is in normal external trigger, the camera will perform sufcient External Keep Clean Cycles to
ensure the Image area is fully cleaned before it will accept an external trigger. Once this period has passed, Normal and
Fast External Triggers operate the same.
Fast External Trigger is useful in those cases where there is very little background light and the user is looking for the
fastest frame rate. With Fast External Trigger, you may see variation in the background contribution to the signal from light
that may have been allowed to fall on the sensor during the readout of the previous image. Fast external trigger does not
mean that when a trigger is accepted the system will respond quicker than in normal external trigger mode.
Figure 29: External Trigger in Non-Frame Transfer mode
NOTE: If the trigger occurs at the early phase of the Keep Clean Cycle, the light signal will not be lost during the
completion of the cycle because only one vertical shift will have occurred. For pulsed light of very short duration
(of the order of one vertical shift), the resultant image may appear to have shifted one row.