Active Filters

Filters are used in a wide variety of electronic
applications. Band-pass filters are used in the field of
telecommunications for speech processing. High-frequency
band-pass filters are used for channel selection in many telephone
applications. Digital signal processing systems use low-pass
anti-aliasing filters as well as low-pass noise filters in conditioning
stages. Power supplies use band-rejection filters to suppress line
frequency signals and high frequency components. Additionally,
filters can be specifically designed to provide phase shifts to each
frequency component while not filtering any frequencies. Active
filter schemes use operational amplifiers, or other active
components, in conjunction with resistors and capacitors to
provide filtering without the need for large inductors as required
in passive filtering. This paper compares the difference between
passive and active filters, and presents all the schemes highlighted
(i.e. low-pass, high-pass, band-pass, band-stop). Popular active
filtering techniques are presented including the Butterworth
filter, Chebyshev filter, and the Bessel filter. The low-pass
Butterworth filter is analyzed in detail, simulation and
experimental results are presented. See "Active Filters" under "papers" on the right for the full document.