Analytic Ladder Design

Abstract

In this Chapter, phase linearity as a major consideration is introduced into the design of low-sensitivity discrete-time filters of the categories defined by the classes of transfer functions presented in Chapter 1. First, emphasis is laid entirely on the phase responses of the filters, but the resulting filters will also possess moderate amplitude selectivity. These will give rise to filters which can be acceptable for some applications in which the phase response is the main design objective while not requiring high selectivity. It is shown that anaytic closed-form expressions exist for the transfer functions of these classes of filters. Next the combined phase and amplitude approximation problem is considered, which leads to filters with flat delay in the passband as well as a moderate degree of amplitude selectivity. For the sake of brevity, we confine our discussion to switched- capacitor filters, and point out that the resulting transfer functions are also realizable in wave digital form, as indicated in Chapter 1.