UnderstandingOscilloscope Functions
20 TDS1000/2000-Series Digital Oscilloscope User Manual
Time Domain Aliasing. Aliasing occurs whenthe oscilloscope does not
sample the signal fast enough to construct a n accurate waveform
record. When this happens, the oscilloscopedisplays a waveform
with a frequency lower than the act ual input waveform, or triggers
and displays an unstable waveform.
Actual high-frequency
waveform
Apparent low-frequency
waveform due to aliasing
Sampled points
The oscilloscope accuratelyrepresents signals, but is limited by the
probe bandwidth,the oscilloscope bandwidth, and the samplerate.
To avoidaliasing, the oscilloscope must sample the signalmore than
twice as fast as the highest frequency component of the signal.
The highest frequencythat 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.