The Nyquist criterion dictates that all signals must be bandlimited to less than half the
sampling rate of the sampling system. Many signals already have a limited spectrum, so
this is not a problem. However, for broad spectrum signals, an analog lowpass filter must
be placed before the data acquisition system. The minimum attenuation of this filter at the
aliasing frequency should be at least:
where B is the number of bits of the ADC. This formula is derived from the fact that there
is a minimum noise level inherent in the sampling process and there is no need to attenuate
the sensor signal more than to below this noise level.