HP 54750A, User Manual, Page: 238 / 478

Increasing Measurement Accurac y
and Time-Interval Measurement
Increasing Measurement Accuracy
Measurement statistics in the instrument give valuable insight. T o view
statistics , select the Dene Measure menu. The Statistics softkey allows you
to display either the minimum and maximum or the mean and standard
deviation of all selected measurements . The most recent value is always
displayed.
Y ou need to know how much the instrument's time-interval measurement
varies statistically because this aects measurements of the statistical
behavior of your system. Jitter introduced by the instrument has two
components: a xed part and a variable part. The xed component of jitter
is the same at all points on the time base , including the trigger point. The
variable component increases as the delay from the trigger point increases .
T o view the xed part of the jitter , set the P osition control in the Time Base
menu to its minimum value . Set the Reference control in the Time Base
menu to Center . Set up the instrument to view a fast-rising edge from a pulse
generator , such as an HP 8131A. The triggered edge should be at the center
of the screen. Press the Trigger menu key . Y ou will see the trigger level
marker displayed on the screen.
Ideally there would be no jitter (no horizontal spreading of the trace) where
the waveform intersects the trigger level. Any spreading is the xed part of
the jitter .
T o view the variable part of the jitter , you must have a synthesized,
crystal-controlled signal source because the source must have less jitter
than the instrument's time base . Y ou can use these HP signal sources to
characterize time base jitter:
HP 8656B (see following paragraph)
HP 8657A (see following paragraph)
HP 3335A synthesized function generator
HP 80000 pulse/pattern generator
The faster the slew rate of the source , the easier it is to evaluate jitter . One
way to get fast-slewing edges is to trigger a pulse generator , such as an
HP 8130A or HP 8131A, with a stable sine-wave source , like an HP 8656B or
HP 8657A.
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