HP 54750A, User Manual, Page: 107 / 478

Eye , Mask and Eyeline Mode Measurement T utorials
Making Eye Diagram Measurements
Measuring fall time
The falling edge of a pulse is dened as a transition that passes through
the upper , middle , and lower threshold or logic levels . F or an edge to be
measured, it must complete the transition through all three threshold
levels . Once a falling transition has been determined, the fall time may be
determined by the following:
(time at the lower threshold crossing) 0 (time at the upper threshold
crossing) = F all time
The instrument has two standard and a user-dened threshold level for which
fall time may be measured. The rst is the 10% to the 90% point on the
transition, and the second is the 20% to the 80% point on the transition.
The 20% to 80% transition is recommended for devices with signicant pulse
distortion. Using the user-dened threshold levels , any point on the transition
may be chosen.
The measurement threshold can be changed by using the 4 Dene meas 5 menu.
Figure 5-11. Fall time measurement.
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