Electronically Tunable First Order AP/LP and LP/HP Filter Topologies Using Electronically Controllable Second Generation Voltage Conveyor (CVCII)

Abstract

In this paper two new first order filter topologies realizing low-pass/all-pass (LP/AP) and low-pass/high-pass (LP/HP) outputs using electronically controllable second generation voltage conveyors (CVCIIs) are presented. Unlike second generation voltage conveyors (VCII), in CVCII each performance parameter, including ports, parasitic impedances, current and/or voltage gains can be electronically varied. Here, in particular, the proposed filter topologies are based on two CVCIIs, one resistor and one capacitor. In the first topology VLP/IAP/VAP and in the second topology ILP/VLP/IHP/VHP outputs are achievable, respectively. However, the current and voltage outputs are not achievable simultaneously and a floating capacitor is used. A control current (Icon) is used to change the first CVCII Y port impedance, which sets the filter −3 dB frequency (f0) of all the outputs. Moreover, in the second topology, the gains of HP and AP outputs are electronically adjusted by means of a control voltage (Vcon). Favorably, no restricting matching condition is necessary. PSpice simulations using 0.18 µm CMOS technology and supply voltages of ±0.9V show that by changing Icon from 0.5 µA to 50 µA, f0 is varied from 89 kHz to 1 MHz. Similarly, for a Vcon variation from −0.9 V to 0.185 V, the gains of IAP and IHP vary from 30 dB to 0 dB and those of VAP and VHP vary from 100 dB to 20 dB. The total harmonic distortion (THD) is about 8%. The power consumption is from 0.385 mW to 1.057 mW.