Oscilloscope Familiarization Labs
2
3000 X-Series Oscilloscopes Advanced Training Guide
29
The height of the glitches should now appear much more stable as shown
in
. When the
Peak Detect
acquisition mode has been selected,
rather than sampling waveforms at a reduced rate, the scope intelligently
decimates acquired data at a higher sample rate. For example, let’s assume
that the scope needs to run at a sample rate that is 1/100th of its
maximum sample rate. This would be equivalent to running the scope at
its maximum sample rate, but only storing every 1/100th point, which is
“unintelligent” decimation. In the Peak Detect mode, the scope would
analyze a group of 200 consecutive samples in real- time (sampled at a
high rate), and then store just the maximum and minimum digitized values
for this group of 200 points, which is just 2 points. This would be a
decimation factor of 100.
So you may ask why not always use the
Peak Detect
mode? There are some
tradeoffs when using this mode of acquisition. First of all, the scope’s
absolute maximum sample rate is reduced. Secondly, stored points will
NOT be evenly spaced. And this is an important criterion of the Nyquist
Sampling theorem. So for this particular measurement application, using
the
Peak Detect
mode is a good choice. But for other measurement
applications,
Peak Detect
may not be the appropriate acquisition mode.
To learn more about oscilloscope real- time sampling, refer to Agilent’s
Application Note titled, “
Evaluating Oscilloscope Sample Rates vs
Sampling Fidelity
Figure 14 The Peak Detect acquisition mode reliably captures the narrow glitches riding
on the slow sine wave.