Trigger Gating: Circulating Loop and
Burst Data Analysis with the Agilent
86100A Infiniium DCA Wide Bandwidth
Oscilloscope
Copyright ã 2000
Agilent Technologies, Inc.
Trigger Gating: Circulating Loop and Burst Data Analysis
with the Agilent 86100A Infiniium DCA Wide Bandwidth
Oscilloscope
There are experiments incorporating wide-bandwidth oscilloscopes that require select
portions of a waveform to be viewed while other portions of the waveform are
intentionally ignored. Examples include circulating loops, or data that occurs in bursts.
In the specific example of the circulating loop, signal propagation through an extremely
long length of fiber, typically in excess of 1000 km, is simulated with multiple
circulations through a shorter length of fiber. For example, a 9000 km trans-pacific fiber
link can be simulated by routing a signal 18 times through a loop of fiber 500 km in
length.
When an oscilloscope is used to view such a signal, the instrument should only sample
the elements that have propagated the correct number of circulations. Thus the
oscilloscope needs to be synchronized with the signals used to control the loading and
circulation within the loop.
Wide-bandwidth oscilloscopes typically require a signal synchronous to the data as a
timing reference. For each trigger edge/event, one and only one data point is sampled.
To acquire a waveform that is composed of 1000 data points, 1000 trigger edge/events
must be responded to by the oscilloscope. The Agilent 86100 Infiniium DCA has an
external BNC connector port called the trigger gate. This port responds to TTL
compatible signals. With the trigger gate feature enabled, a high voltage at the port will
enable the oscilloscope to respond to trigger edges and thus acquire data. When the
signal at the port is low, the oscilloscope will not respond to triggers even if they are
presented to the instrument. They are simply ignored and waveform data is not captured.
An example of the control signals used in a circulating loop experiment is shown in
figure 1. The basic process is to configure the switching to load the loop with data, and
then close the loop so that the data continuously propagates around the loop. Once the
data has traversed the loop the correct number of times, the oscilloscope is gated to allow
it to respond to the always-present trigger signal and acquire only this portion of data. It
is important to note that the signals used to control the loop switches as well as the signal
used to gate the oscilloscope are defined and provided by the user. The oscilloscope
itself does not generate or control any of these signals.
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