ABSTRACT
A filter is a device or network for separating signals on the basis of their frequency. Filters can either be defined in terms of their pass band only where, the frequencies of interest are allowed through, or in term of their stop band, where certain frequencies are removed. The default design mode for most filters is as a low pass where all frequencies below a cutoff frequency, and extending down to dc, are allowed to pass. A simple re-arrangement usually allows for a high pass to be made, where all frequencies above a cutoff frequency, and extending upward, are transmitted. Other mode complex responses such as bandpass are constructed from these basic elements.
