Filter active

A active filter is a Circuit built around an operational Amplifier , itself generally consisted of several Transistor S of the type bipolar or with field effect. It carries out the filtering and the Amplification of the signal which crosses it. Contrary to its passive counterpart , the active filter can possibly present a profit in tension superior to one. Moreover, it with the advantage of being more reliable (all the production line is automated), less expensive (when produced in great quantities), more compact (the parasitic elements resistances, capacities, inductances are thus reduced) and thus integrable within a Integrated circuit. One recognizes nevertheless with the active filter several disadvantages like a bad behavior in high frequencies (reduction of the Band-width, which tend to limit its use to the applications Audio), a great sensitivity to the precision on the value of the component (which generally deviates from the face value from at least 10%), the need for an additional energy source and the limitation of the amplitude of the signals to the order of the Volt. Moreover, the operational amplifiers generate Bruit. Historically, first discrete filters RCAO (Circuit RC + amplifier operational) make their appearance in the middle of the Sixties. It is necessary nevertheless to wait the years septantes with the first commercial integrated circuits (DIFFICULTY, then DIP) so that the economic interest of this type of filter is revealed. For the current applications of the filters (inter alia, credits), to see the article on the electronic filters.

Ideal and real specifications

Methods of approximation of the filters

Sensitivity to the value of the components

Synthesis of complex filters

See too

  • passive Filter

  • Filters used in wiring for sound

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