Agilent Technologies 3458A User Manual page 354

354 Appendix E High Resolution Digitizing With the 3458A
TRIG is the next condition to be satisfied. Only after both TARM and TRIG event
conditions are satisfied can a burst measurement be made with NRDGS. Refer to
Figure 56.
NRDGS [# of readings] [,event]
lets you specify the number of readings to take, the trigger condition for each
reading, and the number of readings saved in memory before or after the trigger
event.
The SWEEP and SSRC commands are specifically designed to make the task of
digitizing easier. The
SWEEP [effective interval between readings] [, number of readings]
command combines the NRDGS parameters with TIMER. SSRC selects the
synchronizing source for subsampling, either external or level. Both the SWEEP
and SSRC commands are used for SSAC (subsampled, AC coupled) and SSDC
(subsampled, DC coupled), and the NRDGS and TRIG are ignored. For DSAC
(direct sampled, AC coupled) and DSDC (direct sampled, DC coupled) all
triggering commands are valid but the use of both in the same measurement is not
recommended.
Figure 56. Once the
trigger arming and
trigger event conditions
are satisfied, a burst of
measurements can
digitize a wave form as
shown in this example.
The SSRC command offers you either internal level triggering or synchronization
with the external trigger. In the subsampling mode, the SSRC EXT calculates the
number of external triggers it needs to accomplish the measurement you specify
with the SWEEP command.
For example, if you want to capture a wave form with 100 ns time resolution for
4096 readings
[SWEEP 100E-9,4096]
the 3458A multiplies the number of readings by the time interval and divides by
the minimum time between samples.
Delay can be used in conjunction with external trigger synchronization to window
your measurement to examine the parts of the wave form you want to see in detail.
For example, consider using the 3458A as a broadband phase/gain meter with a
3325A source to measure the transfer function of a passband filter over a frequency
range of 0.5 to 5 MHz. Refer to Figure 57. The highest frequency is 5 MHz so the
minimum time between samples for entire band is 100 ns for two samples per