RF and microwave high-Q floating active inductor design and implementation P. Branchi 1 , L. Pantoli 2 , V. Stornelli 2 and G. Leuzzi 2, * ,† 1 Altran Italia S.p.A., via Tiburtina 1232, Roma 00131, Italy 2 Department of Industrial and Information Engineering and Economic, University of L’Aquila, Località Campo di Pile, via Gronchi 18, L’Aquila 67040, Italy SUMMARY In this paper, a high-Q floating active inductor (FAI), suitable for RF and microwave applications, is presented. The proposed FAI is based on two cascaded pairs of highly linear capacitance gyrators, which provide a symmetric and reciprocal structure. The proposed FAI shows fully symmetrical two-port characteristics, high quality factor and high linearity. As a feasibility demonstration, a prototype of the designed FAI has been fab- ricated, together with an LC series band-pass filter. At the operating frequency, the real part of the impedance of the equivalent FAI is very low (Req= 0.0039 Ω), providing a very high quality factor. The filter has a central frequency of 430 MHz and a À3dB bandwidth of about 9MHz. Copyright © 2014 John Wiley & Sons, Ltd. Received 1 October 2013; Revised 18 February 2014; Accepted 22 February 2014 KEY WORDS: floating active inductor; active filter; high dynamic range; gyrator 1. INTRODUCTION In the last years, many systems have been successfully implemented in monolithic form for size scaling and system integration, for applications in the telecommunications field. However, most Tx/Rx systems still use off-chip elements for filters, because passive elements, and especially inductors, usually have poor quality factor. Moreover, passive elements often occupy the largest part of the semiconductor area in an RF monolithic circuit. Additionally, spiral inductors have a fixed inductance value, reducing the tuning range of tunable LC filters. So far, several papers have been presented in the literature describing integrated solutions, using equivalent active inductors instead of passive, spiral inductors. These circuits are generally grounded [1–5] or floating [6–20] active inductors. Nevertheless, up to now, there is a lack in the commercial market of such a kind of solutions being necessary a further theoretical and practical significant effort in this field. In this paper, a high-Q reciprocal floating active inductor (FAI), suitable for integrated RF and microwave applications, is presented. The FAI has been designed and characterized by means of a standard two-port network in a ‘pi’ configuration. A prototype of the designed FAI has been realized in hybrid form as a demonstrator, together with its application in a simple first-order active band-pass filter. The paper is organized as follows: the proposed FAI design method is presented in section 2. In section 3, an equivalent model approach for the design and optimization of the FAI is presented. In section 4, the practical implementation of a FAI is described. In section 5, an LC series band-pass filter including the novel active inductor is described, while in section 6 some important remarks are made. Finally, in the Appendix, derivation of the formulas used in section 3 is given. *Correspondence to: G. Leuzzi, Department of Industrial and Information Engineering and Economic, University of L’Aquila, Località Campo di Pile, via Gronchi 18, L’Aquila 67040, Italy. † E-mail: giorgio.leuzzi@univaq.it Copyright © 2014 John Wiley & Sons, Ltd. INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS Int. J. Circ. Theor. Appl. (2014) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cta.1991