Experimental Verification of Pseudo-Differential Electronically Controllable Multifunction Filter Using Modified Current Differencing/Summing Units

Abstract

This paper presents the synthesis and analysis of reconfigurable frequency filter with differential input and differential output terminals and its experimental verification. The inner structure of the filter has single-ended form, i.e., filter behaves as the so-called pseudo-differential circuit. Filtering function can be electronically reconfigured between low-pass (LP) and band-pass (BP) responses. Active elements of the filter are differential voltage buffer (DVB) as an input stage and modified current differencing unit (MCDU) together with modified current summing unit (MCSU) as the inner and also output stage. Each of the important parameters of the filter (angular pole frequency, quality factor and pass-band gain) is electronically controllable by parameters of these active elements used. Some of the parameters of the filter are controlled by two independent parameters, i.e., are dual-controlled, which enables the extended electronic controllability. The proposed topology operates in the voltage mode and both input nodes have high input impedance. Expected behavior of the filter is analyzed and verified by PSpice simulations using CMOS models of above-mentioned active elements. Moreover, features of the filter in both configurations were successfully verified also by experimental measurements using behavioral models of active elements.