Triggering on Waveforms
TDS 684A, TDS 744A, & TDS 784A User Manual 3–79
whether to trigger on edges with slew rates faster than or slower than that
indicated in readout, do the following step:
Press TRIGGER MENU ➞ Type (main) ➞ Pulse (pop-up) ➞ Class (main) ➞
Slew Rate (pop-up) ➞ Trigger When (main) ➞ Trigger if Faster Than or
Trigger if Slower Than (side). (See Figure 3–46.)
NOTE. If you select Trigger if Faster Than and the oscilloscope does not trigger,
it may be because the pulse edge is too fast rather than too slow. To check the
edge speed, switch to edge triggering. Then trigger on the pulse edge and
determine the time the edge takes to travel between the levels set in the slew rate
Thresholds menu. The oscilloscope cannot slew rate trigger on pulse edges that
traverse between threshold levels in 600 ps or less.
Also, to reliably slew rate trigger, a pulse must have a width of 7.5 ns or more. A
pulse of less width may trigger on the wrong slope or not trigger at all. Switch to
edge triggering and check the pulse width if you can’t slew rate trigger as
expected.
Trigger Bar at Upper Threshold
Trigger Bar at Lower Threshold
Cursors Measure Slew Rate
Components of Pulse Edge—dv and dt
Trigger Point at Second Crossing
Figure 3–46: Main Trigger Menu — Slew Rate Class