Introduction

Depending on the specifications, the required order of the filter may be small or big. For less challenging requirements, a second-order or even a first-order section may be adequate. However, higher-order sections may become necessary in other situations. For higher-order filter requirements, either the direct form approach is used, or a combination of secondorder second sections is used which are connected in a cascade form or in a multiple-loop feedback form. Hence, the study of and realization methods of second-order sections assumes importance as they are used either stand-alone or form the building blocks for higher-order filters. Since the overall performance of the higher-order filter depends on the individual second-order building blocks, it is very important that these building blocks have desirable and attractive properties; the following are some such requirements.

A large number of second-order active building blocks are available with each one claiming advantages over the others. Study of the development procedure of such sections might help the readers to gain more insight towards selecting the optimal section or help in designing new circuits/improving upon the existing ones.

Hence, we begin the study of development of second-order sections using a single passive feedback in Section 7.2; the effect of using different types of passive structures in the feedback is also included.