Acquiring Waveforms
TDS5000 Series User Manual
3-33
The oscilloscope uses equivalent-time sampling to extend its sample rate beyond
its real-time maximum sampling rate, but only under two conditions:
H Equivalent Time Auto must be selected. (Acquisition tab of the Horizontal/
Acquisition Setup control window).
H The time base of the oscilloscope is set to a sampling rate that is too fast to
allow it to get enough samples with which to create a waveform record using
real-time sampling.
If both conditions are met, the oscilloscope takes a few samples with each trigger
event and eventually obtains enough samples to construct a waveform record. In
short, the oscilloscope makes multiple acquisitions of a repetitive waveform to
obtain the sample density required for one complete waveform record. (See
Figure 3--13.) Equivalent-time sampling should only be used on repetitive
signals.
1st acquisition cycle
3rd acquisition cycle
nth acquisition cycle
2nd acquisition cycle
Record points
Figure 3- 13: Equivalent-time sampling
The sampling speeds and the number of channels you choose affect the mode
that the oscilloscope uses to sample waveforms:
H The oscilloscope always uses real-time sampling at slower time base
settings. Faster time settings force the oscilloscope to switch from real-time
sampling to equivalent-time sampling, if Equivalent Time Auto is enabled.
H The oscilloscope extends the limit at which it must switch from real-time
sampling by using the digitizers of channels that are turned off to sample the
channel or channels that are turned on.
Equivalent-time Sampling
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