Acquisition Control 13
Keysight InfiniiVision 3000T X-Series Oscilloscopes User's Guide 217
Overview of Sampling
To understand the oscilloscope's sampling and acquisition modes, it is helpful to
understand sampling theory, aliasing, oscilloscope bandwidth and sample rate,
oscilloscope rise time, oscilloscope bandwidth required, and how memory depth
affects sample rate.
Sampling Theory
The Nyquist sampling theorem states that for a limited bandwidth (band-limited)
signal with maximum frequency f
MAX
, the equally spaced sampling frequency f
S
must be greater than twice the maximum frequency f
MAX
, in order to have the
signal be uniquely reconstructed without aliasing.
f
MAX
= f
S
/2 = Nyquist frequency (f
N
) = folding frequency
Aliasing
Aliasing occurs when signals are under-sampled (f
S
< 2f
MAX
). Aliasing is the signal
distortion caused by low frequencies falsely reconstructed from an insufficient
number of sample points.
Figure 34 Aliasing
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