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10.2 Understanding digital triggering
Technically speaking, there are two approaches to determine the known, pre
-
defined situation of the signal: analog or digital.
Each channel in the GEN series system is equipped with a digital trigger
detector. Digital triggering has the benefit of stable vertical reference levels, no
horizontal jitter, and not depending on signal frequency.
A disadvantage of a digital trigger detector is its inability to detect events that
occur between two consecutive samples. This does not usually interfere with
normal operation because the event is not recorded anyway.
10.2.1 Digital trigger detector
Figure 10.1 shows a simplified diagram of a single
-
level digital trigger detector.
Digitized values coming from the ADC are fed into an Arithmetic (and) Logic
Unit – ALU. The value that comes out of the ALU is then referenced against a
preset value (trigger level). The result can be either positive, i.e. the value is
larger, or negative, i.e. the value is smaller. Based on this information, the level
crossing detector verifies if a level crossing in the correct direction has occurred
and, if so, sends out a trigger.
Trigger
ADC DATA
Compare value
+
Level crossing
detected
DELA
Y
ALU
Figure 10.1: Single
-
level trigger detector
The delay register in front of the ALU is used to compare the ADC value with
“older” values. This means that triggering does not react to specific levels, but
to the differential signal or
slope .
GEN3i
144 I3763-3.1 en HBM: public