Categorization of Filters Low-pass filter (LPF) High-pass filter (HPF) Bandpass filter (BPF) Bandstop filter (BSF) arbitrary type etc. In each category the filter can be further divided into active and passive types. In active filter there can be amplification of the of the signal power in the passband region passive filter do not provide power amplification in the passband. Filter used in electronics can be constructed from resistors inductors capacitors transmission line sections and resonating structures (e.g. piezoelectric crystal, Surface Acoustic Wave (SAW) devices and also mechanical resonators etc.). Active filter may contain transistor FET and Op-amp. Filter LPFBPFHPF ActivePassiveActivePassive