Specifications

18
Important Oscilloscope Performance Properties (continued)
Sample rate
Sample rate
The sample rate of an oscilloscope
is the number of samples the
oscilloscope can acquire per
second. It is recommended that
your oscilloscope have a sample
rate that is at a least 2.5 times
greater than its bandwidth.
However, ideally the sample rate
should be 3 times the bandwidth
or greater.
You need to be careful when you
evaluate an oscilloscope’s sample
rate banner specifications.
Manufactures typically specify
the maximum sample rate an
oscilloscope can attain, and often
this maximum rate is possible
only when one channel is being
used. If more channels are used
simultaneously, the sample
rate may decrease. Therefore,
it is wise to check how many
channels you can use while
still maintaining the specified
maximum sample rate. If the
sample rate of an oscilloscope is
too low, the signal you see on the
scope may not be very accurate.
As an example, assume you are
trying to view a waveform, but
the sample rate only produces
two points per period (Figure 26).
Now consider the same waveform,
but with an increased sample
rate that samples seven times per
period (Figure 27).
It is clear that the greater the
samples per second, the more
clearly and accurately the
waveform is displayed. If we
kept increasing the sample rate
for the waveform in the above
example, the sampled points
would eventually look almost
continuous. In fact, oscilloscopes
usually use sin(x)/x interpolation
to fill in between the sampled
points.
For more information about
oscilloscope sampling rates,
see Application Note 1587,
Evaluating Oscilloscope Sample
Rates vs. Sampling Fidelity:
How to Make the Most Accurate
Digital Measurements.
Figure 26. Waveform where the
sample rate yields two data points
per period
Figure 27. Waveform where the
sample rate yields seven data
points per period
Oscilloscope Fundamentals