Advantages of real-time sampling include the following:
•
Usable for single-shot measurements
•
Acquires a complete record of each edge on each trigger.
Disadvantages of real-time sampling include the following:
•
Sampling rate limits the bandwidth
•
Memory depth limits the time resolution
•
Slow sweep speeds increase the possibility of aliasing (see "Bandwidth,
Sampling Rate, and Reconstruction" in this section).
Equivalent-Time Sampling
In equivalent-time sampling, the signal is constantly sampled and digitized at
a rate determined by the oscilloscope’s sampling clock (see figure 21).
Whenever a trigger event occurs, the oscilloscope measures the time from
the trigger event to the next sample. Knowing this time relationship allows
the oscilloscope to assign the samples to the correct time relative to the
trigger. After enough acquisition cycles have occurred, the waveform is
completely defined. Equivalent-time sampling requires a repetitive signal.
Because the sampling phase is random with respect to the input signal,
equivalent-time sampling is very insensitive to aliasing on repetitive signals.
Measurements
Time-interval measurements
13–47
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