Filter

A filter is the field of signal processing removes unwanted components from a signal. Filters can fall into many categories, with some instances overlapping, such as analog/digital, linear/non-linear, passive/active, etc.

Technical Details

By far the most common type of filters are linear continuous-time filters. These filters are meant to remove certain frequencies while allowing others to pass.

Common Terminology

• Low Pass Filter – frequencies below a threshold are passed while high frequencies are attenuated
• High Pass filter – frequencies below a threshold are passed while low frequencies are attenuated
• Band Pass filter – only frequencies withing a certain band are passed
• Band Stop filter – only frequencies withing a certain band are attenuated.
• Notch filter – a very small band Band-stop filter that cuts out one specific frequency
• Comb filter – has multiple, narrow pass bands, regularly spaced
• All Pass filter – passes all frequencies but modifies the phase
• Cutoff frequency - frequency beyond while signals will be passed
• Roll-off - rate of attenuation above the cutoff frequency
• Transition band - the band between the start- and stop-band
• Ripple - the variation insertion loss in the passband of the filter

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