A new electronically tunable first-order all-pass filter using only three NMOS transistors and a capacitor

Abstract

In this paper, a new first-order voltage-mode (VM) all-pass filter that consists of only three NMOS transistors and a capacitor is proposed. The resonance frequency of the proposed circuit can be tuned electronically by a control current. It has high input impedance; thus, it can be easily cascaded with other VM circuits. Furthermore, it does not require any critical passive component matching conditions. Nevertheless, it does not have low output impedance. Although a floating capacitor is used in the proposed circuit, it can be easily realized with today’s technologies. Ideal and nonideality analyses are performed for the proposed circuit. The behavior of the filter is verified by a number of SPICE simulations and an experimental test. The total harmonic distortion variations of the proposed circuit are found low enough.