Chapter 2 145
Making Measurements
Example 11: Time-Gated Measurement
Figure 2-75 Positioning the Gate
You have flexibility in positioning the gate, but some positions offer a
wider choice of resolution bandwidths. A good rule of thumb is to
start the gate in the middle of the pulse and have it remain on for
one-fourth the pulse duration. Doing so provides a reasonable
compromise between setup time and gate length, but it is only a
starting point—you can actually position the gate almost anywhere
you wish.
Figure 2-76 Best Position for Gate
As a general rule, you will obtain the best measurement results if
you position the gate relatively late within the signal of interest, but
without extending the gate over the trailing pulse edge or signal
transition. Doing so maximizes setup time and provides the
resolution bandwidth filters of the spectrum analyzer the most time
to settle before a gated measurement is made. "Relatively late," in
this case, means allowing a setup time of greater than 2 divided by
the resolution bandwidth.
As an example, if you want to use a 1 kHz resolution bandwidth for
measurements, you will need to allow a setup time of at least 2 ms.
Or, if you want to turn on the gate as early as possible, you could use
the widest specified resolution bandwidth in the analyzer, which is 2
MHz. Minimum setup time (2 divided by 2 MHz), equals 1.0 µs, so
you could have a setup time as short as 1 µs, although the minimum
gate delay that can be set is 3 µs.
To Next Page
Loading...
Need help?
General
