Active Filters

An electronic filter is a device that transforms an input signal in some specified way to produce the output signal. The filters discussed in this chapter are specified in the frequency domain, and attenuate a range of frequencies. Filters are classified according to the way groups of frequencies are transmitted, as low-pass, high-pass, pass-band, and band-stop. The frequency response of ideal filters are depicted in figure 1. The transfer function of a real filter will only approximate these response. For the linear filters that we will discuss, filters can be approximated by