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Understanding Oscilloscope Functions
20
TDS1000/2000-Series Digital Oscilloscope User Manual
Time Domain Aliasing. Aliasing occurs when the oscilloscope does not
sample the signal fast enough to construct an accurate waveform
record. When this happens, the oscilloscope displays a waveform
with a frequency lower than the actual input waveform, or triggers
and displays an unstable waveform.
Actual high-frequency
waveform
Apparent low-frequency
waveform due to aliasing
Sampled points
The oscilloscope accurately represents signals, but is limited by the
probe bandwidth, the oscilloscope bandwidth, and the sample rate.
To avoid aliasing, the oscilloscope must sample the signal more than
twice as fast as the highest frequency component of the signal.
The highest frequency that the oscilloscope sampling rate can
theoretically represent is the Nyquist frequency. The sample rate is
called the Nyquist rate, and is twice the Nyquist frequency.