Spreadsheet for simulating aliasing

[calzap]

Attached is an Excel 2007 spreadsheet that simulates aliasing that sometimes occurs with digital oscilloscopes.  I created the spreadsheet so I could understand the phenomenon better.  Aliasing is when a waveform appears on the display that is of lower frequency than the input waveform and can happen when the sampling frequency of the scope is lower than the frequency of the input waveform.  The scope is snatching samples from different cycles of the input and constructing a lower frequency waveform from the samples.  The spreadsheet is setup for a sine wave, but can easily be changed to another type.  There are two examples in the spreadsheet.  One is the obvious case where the sampling interval is an integer or half-integer multiple of Pi times the period of the input signal.  At least in this case, the displayed peak-to-peak amplitude is correct even though the frequency is wrong.  The other example is where the sampling interval is an out of phase factor times the period of the input signal.  In this example, both the peak-to-peak amplitude and frequency are wrong.  There is a good discussion and instructive graphs of aliasing on Wikipedia.

Mike in California