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2
Oscilloscope Familiarization Labs
Figure 5
Performing additional pulse parameter measurements on a digital pulse.
Your scope’s display should now look similar to Figure 5. If Fall Time was
the last measurement that you selected, then the cursors will show where
this measurement is being performed.
At this point, you may be wondering what the difference is between the
“top” of a waveform (Vtop) versus the “maximum” of a waveform (Vmax),
as well as the difference between the “base” of a waveform (Vbase) versus
the “minimum” of a waveform (Vmin).
Vtop is the steady- state high level of the waveform. This is the voltage
level of the waveform after the overshoot and ringing have settled.
Likewise, Vbase is the steady- state low level of the waveform. For digital
pulse parameter measurements, Vtop and Vbase are often more important
parameters to measure than the absolute maximum and minimum voltages
of the waveform (Vmax and Vmin), which are the peak values of the
overshoot.
The Rise Time and Fall Time measurements that we performed are relative
transition times. This means that they have been performed relative to
specific voltage threshold levels. The scope’s default threshold levels for
these measurements are the 10% and 90% levels relative to Vbase and
Vtop. But many of today’s higher speed devices have specified rise and fall
times relative to 20% and 80% threshold levels, or perhaps relative to
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4000 X-Series Oscilloscopes Advanced Training Guide