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AN2668 Nyquist theorem and oversampling
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2 Nyquist theorem and oversampling
The Nyquist theorem states that in order to be able to reconstruct the analog input signal,
the signal should be sampled at a rate f
S
(sampling frequency) that is greater than twice the
maximum frequency component of the input signal.
Not respecting the Nyquist theorem causes aliasing effects and the analog signal cannot be
fully reconstructed from the input samples. Therefore, in most applications, a low-pass filter
is required at the ADC input to filter frequencies lower than half the sampling frequency. It is
difficult to handle the filter constraints with low sampling frequencies.
Oversampling consists in sampling the input analog signal at rates higher than the Nyquist
frequency limit, filtering the samples and reducing the sample rate by decimation. Using this
method relaxes the anti-aliasing low-pass filter constraints.