Filters

Electrical filters perform signal processing functions and can remove unwanted frequencies from signals, enhance wanted ones or both. They suppress interference and reduce background noise. They can be used with resistors, capacitors or inductors and these linear filters are passive as they do not depend on an external power supply and have no active components like transistors. There are various types of filters. Filters can be passive or active, analogue or digital, high-pass, low-pass, band-pass, band-stop or all pass. Alternatively, they can discrete time or continuous time, linear or non-linear, infinite impulse response (IIR) or finite pulse response (FIR). The most common is linear although hybrid filters are also possible. Garnet filters are used on microwave frequencies but quartz filters directly convert their own mechanical motion into electrical signals. A low-pass filter through an inductor blocks high frequencies but a high-pass filter through a capacitor does the opposite. One of the main applications of filters is with radio frequencies but they are also useful in the field of image processing. Digital signal processing is the inexpensive construction of a wide variety of filters although it needs a converter. In telecommunications, multiplexing means a wide frequency band divided into channels.