Main classification of filters
According to the processed signal, it is divided into analog filter and digital filter.
According to the frequency band of the signal passed, it is divided into five types: low pass, high pass, band pass, band stop and all pass filter.
Low-pass filter: it allows the passage of low-frequency or DC components in the signal, suppressing high-frequency components or interference and noise;
High-pass filter: it allows high-frequency components in the signal to pass, suppressing low-frequency or DC components;
Bandpass filter: It allows signals in certain frequency bands to pass, suppressing signals, interference and noise below or above this band;
Band-stop filter: It suppresses signals in a certain frequency band and allows signals outside the band to pass, also known as notch filters.
All-pass filter: An all-pass filter means that the amplitude of the signal does not change over the full frequency range, that is, the amplitude gain in the full band is always equal to one. A general all-pass filter is used for phase shifting, that is, to change the phase of the input signal. Ideally, the phase shift is proportional to the frequency, which is equivalent to a time delay system.