Active filters are electronic circuits that use active components, such as transistors or operational amplifiers, to filter or condition a signal. These filters are commonly used in applications where passive filters, such as inductors and capacitors, are not sufficient to meet the performance requirements of the circuit. Active filters are able to provide a wide range of filtering options, such as low-pass, high-pass, band-pass, and band-stop, and can be designed to have a wide range of frequency responses. They are also able to provide gain or amplification, and can be easily adjusted or controlled using external signals. Active filters are commonly used in a wide range of applications, including audio and video processing, communications, and instrumentation.