If the input signal of the oscilloscope is a sinusoidal signal of 100KHz, but the signal frequency of the oscilloscope is 50KHz, how can this be?This is because the sampling rate of oscilloscope is too slow, resulting in the phenomenon of aliasing. Aliasing means that the waveform displayed on the screen is lower than the actual frequency of the signal, or is unstable even though the trigger light on the oscilloscope is on. So, for a waveform of unknown frequency, how to determine whether the waveform displayed has generated overlap? You can slowly change the sweep speed t/div to a faster time base, to see whether the frequency parameters of the waveform change dramatically, if so, that waveform overlap has occurred;Or the wavy waveform stabilizes at a faster time, indicating that waveform overlap has occurred.According to Nyquist's theorem, the sampling rate should be at least 2 times higher than the high-frequency component of the signal to avoid aliasing. For example, for a 500MHz signal, the sampling rate should be at least 1GS/s.There are several simple ways to prevent aliasing:
· adjust sweep speed;
· automatic setting (Autoset);
· try to switch the collection mode to envelop mode or peak detection mode, because envelop mode seeks the extremum in multiple collection records, while peak detection mode seeks the maximum or minimum value in a single collection record. Both methods can detect fast signal changes.
· if the oscilloscope has Insta Vu collection mode, it can be used, because this mode is fast in collecting waveform, and the waveform displayed by this method is similar to that displayed by analog oscilloscope