3.3 REALIZABLE LOW-PASS RESPONSE CHARACTERIZATION

A convenient method of obtaining useful realizable system responses is to approximate the ideal responses in Section 3.1 using the techniques in Section 3.2. In the following sections we describe a group of LP responses obtained in this manner, along with others obtained by special techniques. Most of these responses have been synthesized as lumped-constant filters (see references in Ref. 18), and Zverev [30] tabulates their element values and gives normalized curves of the attenuation, group delay, impulse, and step responses. We often refer to these curves in our discussions.

These derived LP responses are additionally useful, for in Chapter 4 we use suitable frequency transformations to obtain LP, HP, BP, and BS filters. In this manner the approximation problem need not be repeated for each filter type. Furthermore LP denormalization information for these filter types is given there, allowing the LP responses in Ref. 30 to then characterize the HP, BP, and BS filters. Also, we find in Chapter 9 that many digital filters are designed to exhibit the same responses, thus the LP information has yet another benefit.