Digital Filters: An Overview,

To introduce the topic of digital filtering, we first consider how conventional passive filters are constructed. The configuration is a succession of resonant sections connected in cascade, with the resonance contributing either an emphasis pole or an attenuation transmission zero at a particular frequency. Each section is a second order linear system, characterized by a resonant frequency and a Q, or quality factor Figure 1. Such a filter would be specified by a frequency response, and one must determine proper L and C values to implement the design. To convert such a design to digital form, however, one must specify the poles and zeros for the individual second order sections, rather than the L and C values. Since the input must be in digital form, we digress momentarily to consider two important requirements to be observed in the AD conversion of the input signal to the filter.