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The function on the digitizer has to be activated (armed) in reverse order compared to the data flow.
This means that one stage is set up to be prepared to receive data before the preceding stage is set up
to generate data. This is especially important in streaming applications where the DRAM FIFO may
overflow if the triggering is activated before the read-out to the host PC has started.
4.6 Trigger jitter
4.6.1
Trigger jitter definitions
The triggering operation is subject to two different types of jitter,
1. At the trigger input is a Gaussian distributed jitter which affects the timing of the incoming trigger
signal edge. This jitter is called excess jitter and is caused by noise in the input stage. The RMS
value of this excess jitter is 25 ps.
2. The actual sampling process causes a timing uncertainty. Since the trigger is sampled with the trig-
ger clock, the time points for reading the trigger are discrete. The difference between the incoming
physical trigger signal and the digital representation of the trigger is a stochastic variable with a
rectangular distribution. The RMS value of such a process is
The highest resolution is achieved with an external trigger connected to the TRIG connector.
ADQ8-4X has a trigger clock at 4 GSPS,
72 ps RMS (theoretical value),
See
Table 2
for time resolution all the external trigger sources.
/ - 1 /
,
6 /
- . /
0/
Figure 10: Sources of jitter on the trigger signal.
4.6.2
Asynchronous triggering
If the trigger signal is not phase-locked to the reference clock it is called asynchronous. This trigger
does not have a well-determined relation to the sampling clock and will appear at various positions
within the sampling period. The time resolution of an asynchronous trigger connected to the TRIG input
is set by the Trigger Clock (4 GHz). The time resolution for other triggers is determined by the Data
Clock (250 MHz).
The asynchronous trigger will be exposed to both trigger sources from
dent stochastic processes are added to 72 ps. See
sources.
There are some advantages with the asynchronous trigger:
•
Any pattern noise will be reduced in repeated measurements.
•
The trigger resolution of 250 ps can be used for accurate timing calculations. The
contains the information about the trigger time. See
19-2302 A
2020-09-16
TRIGGER_CLOCK_PERIOD
Section
4.6.4.
,
Table 2
Figure
10.
TRIGGER_CLOCK_PERIOD
of 250 ps and a trigger jitter of
2 3 %
4 5!
Section
for time resolution of all the external trigger
Section
4.6.4.
ADQ8-4X Manual
19-2302 A 2020-09-16
19(46)
/sqrt(12).
4.6.1. These indepen-
TIME_STAMP
19(46)
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