Agilent Technologies U3401A User Manual download pdf (Page 3)

triggering point is set to −1V and the triggering slope is set to be negative, then the waveform

displayed is as shown in the right figure below.

The simple scheme works for a large number of waveforms. The triggering level can be

changed accordingly. The duration of the display frame can be computed from the time base

setting of the scope. There are 10 divisions in total across the screen, and multiply the time

base setting (in time-unit per division) by 10 gives the duration of the triggering frame.

3) Why do the waveforms sometimes appear to be unstable on the screen?

A major cause is that the input signal is not periodic and the waveforms in the triggering

frames are not identical, resulting in an unstable waveform which is the overlap of many

non-identical waveforms.

A second possible cause is that the signal is periodic but has a complex shape. In this case,

the triggering circuitry may find more than one triggering point that satisfies the triggering

slope and triggering level requirement, within any one cycle of the input signal. The situation

is shown below.

A third possible cause is that the input signal is contaminated by external noise, which again

leads to a complex waveform. The situation is illustrated below. The solution is to remove

the source of noise or select the triggering point with a steepest slope, which can help to

decrease the noise sensitivity.

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Agilent Technologies U3401A User Manual Page 3