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Renesas Electronics America - Knowledgebase

What do you mean by Filter?

Latest Updated:11/01/2006




Like filters for liquid, gas, and light, an electric circuit that permits only a specific frequency component to pass is called a filter.
An electric filter normally uses the dependency on frequency of the impedance of a capacitor or a coil. A capacitor is used as a high-pass filter because it allows high frequencies to pass while shutting off low frequencies. Conversely, a coil is used as a low-pass filter because it allows low frequencies to pass while shutting off high frequencies. If these two are used together, a band-pass filter that lets only a specific frequency band pass through is created.

Using a large coil is not practical, so a resistor is used instead.
A filter consisting of a capacitor, a coil, and resistors is called a passive filter, and a filter that also uses active elements such as an operational amplifier or a transistor is called an active filter.

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