An anti-alias (or anti-aliasing) filter allows through the lower frequency components of a signal but stops higher frequencies, in either the signal or noise, from introducing distortion. Anti-alias filters are specified according to the sampling rate of the system and there must be one filter per input signal.
to convert a lowpass analog signal to digital format the first requirement is to sample (determine) the magnitude of the analog signal at regular intervals (the sampling rate). These magnitudes are then converted to digital words. Nyquist has shown that the original analog signal can be recovered from these samples, without distortion, provided that the sampling rate is at least twice that of the bandwidth of the original signal (both these are measured in the same units, typically Hertz). If the signal bandwidth is too great, by the above criterion, there will be distortion. This is referred to as aliasing distortion. Thus, for a given sampling rate, the analog signal must be confined to a defined bandwidth. The filter which defines this bandwidth has a lowpass characteristic. Its purpose is to prevent aliasing distortion, and so is defined as an anti-aliasing filter.. ~~~~~ go back with your browser back button. If lost, go home