Question
What is the effect of aliasing on a digital oscilloscope when displaying a waveform?
Answer Options
- A) A false, jittery low-frequency version of the waveform is displayed
- B) The waveform DC offset will be inaccurate
- C) Calibration of the vertical scale is no longer valid
- D) Excessive blanking occurs, which prevents display of the waveform
Correct Answer: A
Explanation
Aliasing is a critical source of error in digital sampling systems, such as a Digital Storage Oscilloscope (DSO), and occurs when the input signal contains frequency components higher than half the oscilloscope’s sampling rate (violating the Nyquist theorem). When this occurs, the ADC cannot accurately measure the signal’s variations.
Since the DSO cannot keep up with the fast signal changes, the high-frequency components are incorrectly interpreted as completely different, much lower-frequency signals. The primary effect of aliasing is that a false, jittery low-frequency version of the waveform is displayed. This incorrect display, which looks nothing like the true waveform, can trick the operator into making inaccurate measurements, highlighting the need for an adequate sampling rate or proper input filtering.
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