Open Before Trigger Mode; Figure 7-4: Timing Diagram: Clean Until Trigger, Open Before Trigger - Teledyne Princeton Instruments Sophia-XO System Manual

Chapter 7
7.3.1.2

Open Before Trigger Mode

With Open Before Trigger shutter mode, the shutter is opened at the beginning of
Clean Until Trigger. As with Normal mode, once the incoming Trigger pulse has been
received, cleaning of the array stops as soon as the current cleaning pattern has been
completed and shifted. Because the incoming trigger is not synchronous with the
cleaning cycle, there is an inherent jitter of up to one cleaning cycle in the system's
response to an incoming trigger. After this, the shutter remains open for the
programmed exposure time, and frame collection can begin.
Figure 7-4
shutter mode. In this figure, system jitter is shown as light gray dashed lines.

Figure 7-4: Timing Diagram: Clean Until Trigger, Open Before Trigger

If the vertical rows are shifted midway when the Trigger pulse arrives, the pulse is saved
until the row shifting is completed, to prevent the CCD from getting out of step. 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.
Exposure
illustrates the timing diagram for Clean Until Trigger, Open Before Trigger
Pgm'd
Clean Until
ACQUIRE
Cleans
Trigger
TRIGGER
Wait For
SHUTTER
Trigger
Open Before
Trigger
t
O
EXPOSING
READOUT
t
C
Expose
Readout
47