COMPUTER-AIDED DESIGN OF A CLASS OF SWITCHED CAPACITOR FILTERS

Abstract

Amplitude selectivity and phase linearity (equivalently constant group delay) in the frequency domain are properties which have a stubborn antipathy towards each other. They resist attempts to incorporate them simultaneously in the design of switched capacitor filters. Until recently, switched capacitor filters were designed on the amplitude basis alone. However, in order to realize the full potential of these filters, they must be capable of use in applications where phase linearity in the passband is an important requirement. In this dissertation, a design technique and the associated algorithm are presented for selective linear-phase low-pass and high-pass switched capacitor filters. The resulting transfer functions are particularly suitable for realization as leap-frog lossless discrete integrator (LWI) switched-capacitor structures. The technique leads to an optimum compromise between amplitude selectivity and passband phase linearity. A second technique for achieving phase linearity is by using switched capacitor all pass structure. An all pass circuit preserves the amplitude variation of a filter while introducing additional phase lag. A switched capacitor all pass filters using two terminal negative impedance building block is given. Finally, a technique for the realization of a narrow-band switched capacitor filter is presented based on the N-path technique. Use of sampling rate alteration is made in this realization.