HP 54750A, User Manual, Page: 247 / 478

Increasing Measurement Accurac y
and Time-Interval Measurement
Time-Interval Measurements
Rise time response
If a step with a Gaussian shape is applied to the input of the instrument,
the measured 10 percent to 90 percent rise time is approximately equal to
the quadrature sum of the rise time of the step and the rise time of the
instrument. The rise time of the instrument depends on which plug-in is
used.
Consider measuring the rise time of a signal that has an actual rise time of
1 ns . If you use an instrument and probe that have a combined rise time of
1 ns , the error will be approximately 40 percent:
M easur ed r ise time =
p
(1 ns)
2
+ (1 ns)
2
= 1: 41 ns
If instead you measure the same signal with an instrument and probe with
a combined rise time of 330 ps , the error will be reduced to approximately
5 percent:
M easur ed r ise time =
p
1 ns)
2
+ (330 ps)
2
= 1: 05 ns
T able 9-1 shows the error for other ratios of instrument rise time to signal rise
time .
T able 9-1. Rise-Time Measurement Errors
Signal Rise Time/
Instrument Rise Time
Measurement
Error %
1 40
2 12
3 5
4 3
5 2
6 1.4
7 1
Y ou can apply the concepts of rise time measurement to measuring the
interval between two identical edges at dierent levels . The error in
9-15