Filter capacitors Capacitors are reactive elements, which make them suitable for use in analog electronic filters. The reason for this is that the impedance of a capacitor is a function of frequency, as explained in the article about impedance and reactance. This means that the effect of a capacitor on a signal is frequency-dependent, a property that is extensively used in filter design. Analog electronic filters are used to perform a predefined signal processing function. An example of such a function is a low-pass filter (LPF), which passes through low frequencies, but blocks high frequencies. Another example is the high-pass filter (HPF), which passes through high frequencies but blocks low frequencies. These are some basic filter types which can be combined to create other more complicated filters, such as band-pass or notch filters. Electronic filters can be realized in many different ways. They can be made using analog components only, such as capacitors, inductors, resistors, transistors, and operational amplifiers. They can also be realized using digital technology - digital signal processing circuits that consist of a specialized computer or microcontroller and software appropriate for the application. Analog filters are further divided into passive and active filters. Active filters use amplifying circuits and components such as transistors and opamps, while passive filters use resistors, inductors and capacitors exclusively. The advantage of passive filters is that no power source is needed apart from the processed signal itself, while the advantage of active filters is reduced size and cost. Line filters A special subset of electronic filters are line filters. They are used to suppress electrical noise coming from the power supply line. There are many sources of power line noise which make the power supply voltage fluctuate at various frequencies. Some noise sources, such as air conditioners, refrigerators, heaters and other large...
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