Keysight 4000 X-Series, Руководство по продвинутой подготовке

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Oscilloscope Familiarization Labs
2
4000 X-Series Oscilloscopes Advanced Training Guide 31
The height of the glitches should now appear much more stable as shown in
Figure 14 . 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.
Figure 14 The Peak Detect acquisition mode reliably captures the narrow glitches riding on
the slow sine wave.