the most common type of oscilloscope
triggering used today
is edge triggering which is the default
on all oscilloscopes
this type of triggering works fine on
repetitive
continuous wave or cw type signals
including clock signals but most of
today's signals are more complex than
that
so what if you're trying to synchronize
on the first pulse of
a burst such as packets of serial data
or perhaps an rf burst will edge
triggering work
hi i'm johnny hancock product manager
for keysight's infiniivision
x-series oscilloscopes let's get started
and see how we can use
simple edge triggering along with
trigger holdoff
to synchronize oscilloscope acquisitions
on a burst
this is a pretty complex signal it's
somewhat difficult to trigger on if
you're just simply using edge
triggering and it right now it just
looks like a blur
because it's updating repetitively and
it's triggering on different pulses
if i press stop on the oscilloscope
now you can see it's a burst of signals
it's an
fm burst it starts at a low frequency
and increases to a higher frequency then
it just goes idle
now if i do several single shot
acquisitions
you can see here it triggered on the
first cycle
there are triggered somewhere in the
middle there are triggered near the end
of the burst and if i press
run then it's just a blur what we would
like the scope to do
is always trigger on the same cycle
within the burst
and the easiest one to trigger on is the
very first one
and we can do that with trigger holdoff
now what is
trigger off what trigger hold off is
is it's basically telling the scope hold
off this much
time before re-arming the trigger
after the previous trigger so let's see
how do we determine
how much trigger hold off to use on this
particular
fm burst application so before i press
run on the scope again i've i've got it
frozen stored on screen
we can make some timing measurements on
this burst i'm going to
turn on the cursors and i'm going to
measure the width
of this burst
x1 cursor at the beginning x2 cursor at
the
end i can see the delta time
it's about 100 microseconds it says 97
100 microseconds is close enough
now how long until the next burst comes
along
well let's move that cursor to the next
burst
and it occurs about 130 microseconds
after the previous burst so that's the
cycle time of the burst
the ideal holdoff time is somewhere
during this uh dead time of the signal
which would be about 115 microseconds
now
110 would work 120 would work
so let me go into the trigger coupling
menu
select hold off and then enter
115 microseconds
and run now you can see the scope
running
repetitively it's the same signal every
time it looks
almost stored but it is running
repetitively
and we're locked on to the first pulse
every time
so here's another example this is a
serial bus
protocol it's called scent single-leg
nibble transmission it's very popular in
automotive
and um right now i'm just triggering on
edges
without trigger holdoff so again i'm
going to press stop
and here i can see each new what they
call
frame or every packet again i'm going to
measure
the delta time of each packet
or burst
and it measures about 700 microseconds
and then the time until the next packet
is about 900 microseconds so somewhere
in between those two
is the perfect hold off time so i'm
going to enter
800 microseconds and that should lock us
in
and press run there we go so now it's
always triggering at the beginning of
the packet
infiniivision's oscilloscopes have a lot
of advanced triggering capability
this is one of the simplest ones just
using trigger hold off
we have the ability to uniquely trigger
on a variety of serial protocols
and also other types of complex signals
but again
trigger hold off is the probably the
simplest way to lock on to
burst of data if you think you might
have learned something in this short
video to make you more proficient
in performing oscilloscope measurements
i invite you to view our
other infiniivision oscilloscope
measurement tips videos
to learn more about keysight's
infiniivision x-series oscilloscopes
go to the url listed on your screen or
contact one of keysight's authorized
distributors thanks and semper fi
you