What Is the Difference Between Active and Passive Filters?

Active filters use amplifiers, and passive filters have no active components in the circuit. Filters of any type are defined as circuits that can modify or reject unwanted frequencies.

According to GlobalSpec, the amplifiers in active filters can either be voltage or operational so as to stabilize the filter's behavior. This amplitude response can be modeled by an ideal frequency response curve. According to Schematica, active filters utilize no inductors but are easier to design than passive filters. The five basic types of active filters are low pass (which reduces frequencies below the cutoff), high pass (which increases frequencies above the cutoff), band pass (which shifts frequencies above and below the cutoff), band reject (which reduces some frequencies and allows others) and universal (which allow the user to make the filter function as any of the other four types). According to Electronic Tutorials, passive filters have similar basic types, but the output level is always lower than the input level. Some disadvantages of active filters include the requirement of a power supply to function unlike passive filters. Schematica shows how active filters can produce high gains, but passive filters do not. GlobalSpec also cites filter characteristics as an important detail to consider when selecting active filters.