Circuit Theory/Filters

From Wikibooks, open books for an open world
< Circuit Theory
Jump to navigation Jump to search
Low pass filter
High pass filter
Band Pass filter
Band Stop filter
Comb filter

Some terms used to describe and classify linear filters:

Frequency Response[edit]

    • Low-pass filter – low frequencies are passed, high frequencies are attenuated.
    • High-pass filter – high frequencies are passed, low frequencies are attenuated.
    • Band-pass filter – only frequencies in a frequency band are passed.
    • Band-stop filter or band-reject filter – only frequencies in a frequency band are attenuated.
    • Notch filter – rejects just one specific frequency - an extreme band-stop filter.
    • Comb filter – has multiple regularly spaced narrow passbands giving the bandform the appearance of a comb.
    • All-pass filter – all frequencies are passed, but the phase of the output is modified.
  • Cutoff frequency is the frequency beyond which the filter will not pass signals. It is usually measured at a specific attenuation such as 3dB.
  • Roll-off is the rate at which attenuation increases beyond the cut-off frequency.
  • Transition band, the (usually narrow) band of frequencies between a passband and stopband.
  • Ripple is the variation of the filter's insertion loss in the passband.
  • The order of a filter is the degree of the approximating polynomial and in passive filters corresponds to the number of elements required to build it. Increasing order increases roll-off and brings the filter closer to the ideal response.