Keysight Technologies DSO-X 2014A, User Manual

Page: 179 / 378

Acquisition Control
12
Keysight InfiniiVision 2000 X-Series Oscilloscopes User's Guide 179
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.
Oscilloscope Bandwidth and Sample Rate
An oscilloscope's bandwidth is typically described as the lowest frequency at
which input signal sine waves are attenuated by 3 dB (-30% amplitude error).
Figure 33 Aliasing