Keysight Technologies DSO-X 2014A, User Manual

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Acquisition Control
12
Keysight InfiniiVision 2000 X-Series Oscilloscopes User's Guide 181
So, in practice, an oscilloscope's sample rate should be four or more times its
bandwidth: f
S
= 4f
BW
. This way, there is less aliasing, and aliased frequency
components have a greater amount of attenuation.
See Also Evaluating Oscilloscope Sample Rates vs. Sampling Fidelity: How to Make the
Most Accurate Digital Measurements , Keysight Application Note 1587
( http://literature.cdn.keysight.com/litweb/pdf/5989-5732EN.pdf )
Oscilloscope Rise Time
Closely related to an oscilloscope's bandwidth specification is its rise time
specification. Oscilloscopes with a Gaussian-type frequency response have an
approximate rise time of 0.35/f
BW
based on a 10% to 90% criterion.
An oscilloscope's rise time is not the fastest edge speed that the oscilloscope can
accurately measure. It is the fastest edge speed the oscilloscope can possibly
produce.
Figure 35 Sample Rate and Oscilloscope Bandwidth
Limiting oscilloscope bandwidth (f
BW
) to 1/4 the sample rate (f
S
/4)
reduces frequency components above the Nyquist frequency (f
N
).
f
S
f
N
f
S
/4
-3dB
Attenuation
Aliased frequency
components
Frequency
0dB