Planar Circular Spiral Inductors With Improved Q and Self-Resonance Frequency Using Compensatory Capacitance Technique

Abstract

This paper presents a planar circular spiral inductor introducing an optimum compensatory ground capacitance to improve its quality factor and self-resonance frequency. The equivalent lumped electrical circuit model of the proposed inductor is developed for both top and bottom layers. In this electrical model, the compensatory capacitance is introduced in series with the substrate capacitance. This compensatory capacitor is in the form of a modified ground conductor, which is realized using a transmission line based technique. The total parasitic capacitance is reduced in this manner, and consequently, the quality factor and self-resonance frequency are increased without any fringing field or back radiation effects. Three circular spiral inductors are fabricated on FR4 substrate to verify the proposed design. The measured results show that the resonance frequency and quality factor are improved as compared to a conventional spiral planar inductor, without any increase in the inductor area. The quality factors are improved by 21.28%, 19.60%, and 17.12% for the inductors having 1.5, 2.5, and 3.5 turns, respectively. In addition, the self-resonance frequency is improved by 27%, 18.05%, and 17.85% for the inductor having 1.5, 2.5, and 3.5 turns, respectively. The proposed inductor design is scalable for different frequencies of operation.