Complex Filters as Cascade of Buffered Gingell Structures: Design from Band-Pass Constraints

• Main Author: Hay, Nicole M
• Format: Others
• Published: DigitalCommons@CalPoly 2017
• Subjects: complex filter; positive frequency; negative frequency; quadrature; cascade; Electrical and Electronics; Systems and Communications
• Online Access: https://digitalcommons.calpoly.edu/theses/1731; https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=2913&context=theses

Complex filters are multi-input, multi-output networks designed to discriminate based upon the relative phase difference between input signals. Complex filters find application in modern wireless systems for single sideband transmission and image-reject reception. This thesis presents one active complex filter implementation using two operational amplifiers per stage, termed “type-II” topology. The “type-II” originates from the passive RC-CR polyphase topology presented by Gingell in his 1973 paper, “Single sideband modulation using sequence asymmetric polyphase networks.” This new topology gains several advantages over existing complex filter implementations, namely “cascadability” (multiple sections placed in series to create a higher-order response) without altering the characteristics of each individual stage. In addition to describing the derivation of the topology and its performance relative to existing topologies, this thesis investigates the passband characteristics of a general higher-order filter and provides a passband-centric design approach through derivations of closed form expressions for passband gain and bandwidth. The thesis includes a five-stage design example using this approach in addition to an implementation, its characterization, and its comparison to the derived expressions and simulations.