The Nyquist sampling requirement can be derived intuitively from our
knowledge of Fourier Series summarized in Chapter 1. We
can view the sampling process as the mixing of the input signal with a train of very
narrow data sampling pulses which will result in sum and difference components appearing
at the mixer output for each harmonic of the pulse waveform mixing with the signal
waveform as shown. This is the spectrum that would effectively appear at the output of a
D/A converter. In order to reconstruct the input waveform correctly, the D/A output
needs to be filtered so that only the spectral components present within the source signal
remain. |