Increasing Measurement Accuracy
and Time-Interval Measurement
Increasing Measurement Accuracy
To see the variable jitter, set Position in the Time Base menu to a large
number relative to the Scale setting. As you increase the value of Position,
you will see the jitter increase. The instrument's variable jitter is on the
order of 10 to 20 ppm, so you must use a large value of Position and a fast
setting of Time Base Scale to see it. You can use the automatic measurements
in the instrument to measure the jitter and observe its statistics.To calculate
the slope of the variable jitter, subtract the xed jitter from the observed
jitter and divide by the Position setting.
The jitter in the instrument has approximately normal distribution. For
measuring jitter that also has a normal distribution, the standard deviations
add in quadrature as shown in equation 1.
Equation
1
(
M
easured
j itter
)
2
=
(
Sig
nal j
itter
)
2
+
(
Scope
j itter
)
2
If
the
standard
deviation
of
the
instrument's
jitter
is
1/3
of
the
standard
deviation
of
the
actual
jitter
,
the
error
in
the
measured
standard
deviation
will
be
about
5
percent.
9-7
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