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4.4 Timestamp
4.4.1
Timestamp definitions
The timestamp counter enables real-time measurement of a trigger event. It is used for tagging an
event, sorting events in time or comparing timing between events.
The timestamp information consist of three parts, which uniquely defines the timing:
•
measures the time of the trigger event relative to other trigger events.
TIME_STAMP
•
is the time between the trigger event and the start of the record. For a pretrigger,
RECORD_START
this is a negative value. When trigger delay is used, this is a positive value.
•
is the length of a sample period. The sample period may vary with sample skip
SAMPLE_PERIOD
setting and clock frequency of the digitizer.
The
,
TIME_STAMP
RECORD_START
= 25 ps. See
TIME_BASE
in the record header, see
The timestamp counter is based on the internal clock of the digitizer. The internal clock is based on the
selected clock reference. The timestamp is thus also related to the clock reference. When the clock ref-
erence is phase-locked to an external source, the timestamp counter is running synchronized with the
external source. On the other hand, if the digitizer is free running, the timestamp counter also free run-
ning. (See
Section 5
for all details about the clock system of digitizer.)
The timestamp counter measures the time from a reference time point to the trigger event. The refer-
ence time point is when the counter is started or reset. See
reset the timestamp counter.
Example 3: Assume an ADQ8-4X sampling with a clock frequency at 2 GSPS. The pretrigger is set to
32 samples and the external trigger is used. The following parameters are returned:
= 5010
TIME_STAMP
= –650
RECORD_START
= 20
SAMPLE_PERIOD
= 25 ps
TIME_BASE
The time for the trigger was then
=
TRIGGER_TIME
TIME_STAMP
The time for the first sample in the record is
= (
RECORD_TIME
TIME_STAMP
The time between two samples are
=
SAMPLE_TIME
SAMPLE_PERIOD
The time from the record start to the trigger is
*
RECORD_START
TIME_BASE
The number of samples between the record start (first sample in the record) and the trigger event is
(
–
TRIGGER_TIME
RECORD_TIME
|
| /
RECORD_START
SAMPLE_PERIOD
This is the expected 32 samples set in the pretrigger and 1/2 sample in subsample precision in the
external trigger.
4.4.2
Timestamp reset
When powering up a system with many boards, the timestamp counter in each board will start. But the
counters start at different times in different physical digitizers. There are four methods for resetting the
timestamp and get a common time reference in all the digitizers in the system:
19-2302 A
2020-09-16
, and
SAMPLE_PERIOD
Example 3
on how to use these parameters. These parameters are available
Section
7.9.1.
*
= 125250 ps = 125.25 ns
TIME_BASE
+
RECORD_START
*
= 0.5 ns
TIME_BASE
= –16.25 ns.
) /
SAMPLE_TIME
= 32.5 samples
are measured in the unit
Section 4.4.2
) *
= 109.000 ps = 109 ns
TIME_BASE
=
ADQ8-4X Manual
19-2302 A 2020-09-16
14(46)
for information on how to
14(46)
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