Design of a variable gain and phase amplifier using double resonance and current conveyor circuits

Abstract

Some radiofrequency applications require control of magnitude and phase of narrowband signals, such as beamforming networks for antenna arrays. An amplifier capable of varying magnitude and phase of a signal through control signals can be called a variable gain and phase amplifier (VGPA). In this paper a VGPA circuit is proposed which utilizes two double resonance circuits, each one with a voltage variable capacitor to produce magnitude and phase variations. To avoid excessive reflections at the output port, and to establish high impedance in certain parts of the circuit, two current conveyor circuits connected as voltage follower are used. Analysis of each stage as well as design methodology is presented. A design example is carried out and graphics for the properties of gain and phase are obtained using simulation tools. Although control of these characteristics is not independent, the advantage is that it can be done by a single circuit.