Design of a Switched-Capacitor Pseudo-2-Path Filter Using Multi-Phase Switched-Opamp Technique

Abstract

High-Q Switched-capacitor (SC) bandpass filters can be realized with SC highpass path-filters using 2-path technique or with SC lowpass path-filters using 3-path technique [VON 83] [ANA 95]. Though the 2-path filter offers better filter performances while employing less path cells, the required SC highpass ladder filters have generally stray-sensitive structures unless those stray-sensitive switching capacitor branches are replaced by opamps [GER 86], which certainly increases the power consumption and therefore is not desired. Meanwhile, SC lowpass ladder filters usually have stray-insensitive structures [GER 86] [ANA 95], and thus a trade-off between power consumption and filter performances seems unavoidable when choosing between 2-path filter and 3-path filter topologies. However, in z-domain, a lowpass response can be transformed to a highpass response by replacing all “z” terms in the transfer function with “-z”, which is known as the “z to —z transformation”. By employing z to —z transformation on a switched-capacitor lowpass filter, a highpass filter can be obtained while inherently enjoying the advantages of the lowpass ladder filter structure without asking for extra.